Clinical Genomics in Inflammatory Bowel Disease.

Trends Genet. 2017 Jul 26;:

Authors: Uhlig HH, Muise AM

Abstract
Genomic technologies inform the complex genetic basis of polygenic inflammatory bowel disease (IBD) as well as Mendelian disease-associated IBD. Aiming to diagnose patients that present with extreme phenotypes due to monogenic forms of IBD, genomics has progressed from 'orphan disease' research towards an integrated standard of clinical care. Advances in diagnostic clinical genomics are increasingly complemented by pathway-specific therapies that aim to correct the consequences of genetic defects. This highlights the exceptional potential for personalized precision medicine. IBD is nevertheless a challenging example for genomic medicine because the overall fraction of patients with Mendelian defects is low, the number of potential candidate genes is high, and interventional evidence is still emerging. We discuss requirements and prospects of explanatory and predictive clinical genomics in IBD.

PMID: 28755896 [PubMed - as supplied by publisher]

Mutations in KDSR Cause Recessive Progressive Symmetric Erythrokeratoderma.

Am J Hum Genet. 2017 Jun 01;100(6):978-984

Authors: Boyden LM, Vincent NG, Zhou J, Hu R, Craiglow BG, Bayliss SJ, Rosman IS, Lucky AW, Diaz LA, Goldsmith LA, Paller AS, Lifton RP, Baserga SJ, Choate KA

Abstract
The discovery of new genetic determinants of inherited skin disorders has been instrumental to the understanding of epidermal function, differentiation, and renewal. Here, we show that mutations in KDSR (3-ketodihydrosphingosine reductase), encoding an enzyme in the ceramide synthesis pathway, lead to a previously undescribed recessive Mendelian disorder in the progressive symmetric erythrokeratoderma spectrum. This disorder is characterized by severe lesions of thick scaly skin on the face and genitals and thickened, red, and scaly skin on the hands and feet. Although exome sequencing revealed several of the KDSR mutations, we employed genome sequencing to discover a pathogenic 346 kb inversion in multiple probands, and cDNA sequencing and a splicing assay established that two mutations, including a recurrent silent third base change, cause exon skipping. Immunohistochemistry and yeast complementation studies demonstrated that the mutations cause defects in KDSR function. Systemic isotretinoin therapy has achieved nearly complete resolution in the two probands in whom it has been applied, consistent with the effects of retinoic acid on alternative pathways for ceramide generation.

PMID: 28575652 [PubMed - indexed for MEDLINE]

Mutations in SULT2B1 Cause Autosomal-Recessive Congenital Ichthyosis in Humans.

Am J Hum Genet. 2017 Jun 01;100(6):926-939

Authors: Heinz L, Kim GJ, Marrakchi S, Christiansen J, Turki H, Rauschendorf MA, Lathrop M, Hausser I, Zimmer AD, Fischer J

Abstract
Ichthyoses are a clinically and genetically heterogeneous group of genodermatoses associated with abnormal scaling of the skin over the whole body. Mutations in nine genes are known to cause non-syndromic forms of autosomal-recessive congenital ichthyosis (ARCI). However, not all genetic causes for ARCI have been discovered to date. Using whole-exome sequencing (WES) and multigene panel screening, we identified 6 ARCI-affected individuals from three unrelated families with mutations in Sulfotransferase family 2B member 1 (SULT2B1), showing their causative association with ARCI. Cytosolic sulfotransferases form a large family of enzymes that are involved in the synthesis and metabolism of several steroids in humans. We identified four distinct mutations including missense, nonsense, and splice site mutations. We demonstrated the loss of SULT2B1 expression at RNA and protein levels in keratinocytes from individuals with ARCI by functional analyses. Furthermore, we succeeded in reconstructing the morphologic skin alterations in a 3D organotypic tissue culture model with SULT2B1-deficient keratinocytes and fibroblasts. By thin layer chromatography (TLC) of extracts from these organotypic cultures, we could show the absence of cholesterol sulfate, the metabolite of SULT2B1, and an increased level of cholesterol, indicating a disturbed cholesterol metabolism of the skin upon loss-of-function mutation in SULT2B1. In conclusion, our study reveals an essential role for SULT2B1 in the proper development of healthy human skin. Mutation in SULT2B1 leads to an ARCI phenotype via increased proliferation of human keratinocytes, thickening of epithelial layers, and altered epidermal cholesterol metabolism.

PMID: 28575648 [PubMed - indexed for MEDLINE]

Biallelic Mutations in CFAP43 and CFAP44 Cause Male Infertility with Multiple Morphological Abnormalities of the Sperm Flagella.

Am J Hum Genet. 2017 Jun 01;100(6):854-864

Authors: Tang S, Wang X, Li W, Yang X, Li Z, Liu W, Li C, Zhu Z, Wang L, Wang J, Zhang L, Sun X, Zhi E, Wang H, Li H, Jin L, Luo Y, Wang J, Yang S, Zhang F

Abstract
Sperm motility is vital to human reproduction. Malformations of sperm flagella can cause male infertility. Men with multiple morphological abnormalities of the flagella (MMAF) have abnormal spermatozoa with absent, short, coiled, bent, and/or irregular-caliber flagella, which impair sperm motility. The known human MMAF-associated genes, such as DNAH1, only account for fewer than 45% of affected individuals. Pathogenic mechanisms in the genetically unexplained MMAF remain to be elucidated. Here, we conducted genetic analyses by using whole-exome sequencing and genome-wide comparative genomic hybridization microarrays in a multi-center cohort of 30 Han Chinese men affected by MMAF. Among them, 12 subjects could not be genetically explained by any known MMAF-associated genes. Intriguingly, we identified compound-heterozygous mutations in CFAP43 in three subjects and a homozygous frameshift mutation in CFAP44 in one subject. All of these recessive mutations were parentally inherited from heterozygous carriers but were absent in 984 individuals from three Han Chinese control populations. CFAP43 and CFAP44, encoding two cilia- and flagella-associated proteins (CFAPs), are specifically or preferentially expressed in the testis. Using CRISPR/Cas9 technology, we generated two knockout models each deficient in mouse ortholog Cfap43 or Cfap44. Notably, both Cfap43- and Cfap44-deficient male mice presented with MMAF phenotypes, whereas the corresponding female mice were fertile. Our experimental observations on human subjects and animal models strongly suggest that biallelic mutations in either CFAP43 or CFAP44 can cause sperm flagellar abnormalities and impair sperm motility. Further investigations on other CFAP-encoding genes in more genetically unexplained MMAF-affected individuals could uncover novel mechanisms underlying sperm flagellar formation.

PMID: 28552195 [PubMed - indexed for MEDLINE]

Clonal selection and double-hit events involving tumor suppressor genes underlie relapse in myeloma.

Blood. 2016 Sep 29;128(13):1735-44

Authors: Weinhold N, Ashby C, Rasche L, Chavan SS, Stein C, Stephens OW, Tytarenko R, Bauer MA, Meissner T, Deshpande S, Patel PH, Buzder T, Molnar G, Peterson EA, van Rhee F, Zangari M, Thanendrarajan S, Schinke C, Tian E, Epstein J, Barlogie B, Davies FE, Heuck CJ, Walker BA, Morgan GJ

Abstract
To elucidate the mechanisms underlying relapse from chemotherapy in multiple myeloma, we performed a longitudinal study of 33 patients entered into Total Therapy protocols investigating them using gene expression profiling, high-resolution copy number arrays, and whole-exome sequencing. The study illustrates the mechanistic importance of acquired mutations in known myeloma driver genes and the critical nature of biallelic inactivation events affecting tumor suppressor genes, especially TP53, the end result being resistance to apoptosis and increased proliferation rates, which drive relapse by Darwinian-type clonal evolution. The number of copy number aberration changes and biallelic inactivation of tumor suppressor genes was increased in GEP70 high risk, consistent with genomic instability being a key feature of high risk. In conclusion, the study highlights the impact of acquired genetic events, which enhance the evolutionary fitness level of myeloma-propagating cells to survive multiagent chemotherapy and to result in relapse.

PMID: 27516441 [PubMed - indexed for MEDLINE]

Mitochondrial Encephalopathy and Transient 3-Methylglutaconic Aciduria in ECHS1 Deficiency: Long-Term Follow-Up.

JIMD Rep. 2017 Jul 29;:

Authors: Huffnagel IC, Redeker EJW, Reneman L, Vaz FM, Ferdinandusse S, Poll-The BT

Abstract
We report the major diagnostic challenge in a female patient with signs and symptoms suggestive of an early-onset mitochondrial encephalopathy. Motor and cognitive development was severely delayed and brain MRI showed signal abnormalities in the putamen and caudate nuclei. Metabolic abnormalities included 3-methylglutaconic aciduria and elevated lactate levels in plasma and cerebrospinal fluid, but were transient. Whole exome sequencing at the age of 25 years finally revealed compound heterozygous mutations c.[229G>C];[563C>T], p.[Glu77Gln];[Ala188Val] in the ECHS1 gene. Activity of short-chain enoyl-CoA hydratase, a mitochondrial enzyme encoded by the ECHS1 gene, was markedly decreased in lymphocytes. Retrospective urine analysis confirms that elevated levels of S-(2-carboxypropyl)cysteamine, S-(2-carboxypropyl)cysteine, and N-acetyl-S-(2-carboxypropyl)cysteine can be a diagnostic clue in the disease spectrum of ECHS1 mutations.

PMID: 28755360 [PubMed - as supplied by publisher]

Pharmacogenetic meta-analysis of baseline risk factors, pharmacodynamic, efficacy and tolerability endpoints from two large global cardiovascular outcomes trials for darapladib.

PLoS One. 2017;12(7):e0182115

Authors: Yeo A, Li L, Warren L, Aponte J, Fraser D, King K, Johansson K, Barnes A, MacPhee C, Davies R, Chissoe S, Tarka E, O'Donoghue ML, White HD, Wallentin L, Waterworth D

Abstract
Darapladib, a lipoprotein-associated phospholipase A2 (Lp-PLA2) inhibitor, failed to demonstrate efficacy for the primary endpoints in two large phase III cardiovascular outcomes trials, one in stable coronary heart disease patients (STABILITY) and one in acute coronary syndrome (SOLID-TIMI 52). No major safety signals were observed but tolerability issues of diarrhea and odor were common (up to 13%). We hypothesized that genetic variants associated with Lp-PLA2 activity may influence efficacy and tolerability and therefore performed a comprehensive pharmacogenetic analysis of both trials. We genotyped patients within the STABILITY and SOLID-TIMI 52 trials who provided a DNA sample and consent (n = 13,577 and 10,404 respectively, representing 86% and 82% of the trial participants) using genome-wide arrays with exome content and performed imputation using a 1000 Genomes reference panel. We investigated baseline and change from baseline in Lp-PLA2 activity, two efficacy endpoints (major coronary events and myocardial infarction) as well as tolerability parameters at genome-wide and candidate gene level using a meta-analytic approach. We replicated associations of published loci on baseline Lp-PLA2 activity (APOE, CELSR2, LPA, PLA2G7, LDLR and SCARB1) and identified three novel loci (TOMM5, FRMD5 and LPL) using the GWAS-significance threshold P≤5E-08. Review of the PLA2G7 gene (encoding Lp-PLA2) within these datasets identified V279F null allele carriers as well as three other rare exonic null alleles within various ethnic groups, however none of these variants nor any other loci associated with Lp-PLA2 activity at baseline were associated with any of the drug response endpoints. The analysis of darapladib efficacy endpoints, despite low power, identified six low frequency loci with main genotype effect (though with borderline imputation scores) and one common locus (minor allele frequency 0.24) with genotype by treatment interaction effect passing the GWAS-significance threshold. This locus conferred risk in placebo subjects, hazard ratio (HR) 1.22 with 95% confidence interval (CI) 1.11-1.33, but was protective in darapladib subjects, HR 0.79 (95% CI 0.71-0.88). No major loci for tolerability were found. Thus, genetic analysis confirmed and extended the influence of lipoprotein loci on Lp-PLA2 levels, identified some novel null alleles in the PLA2G7 gene, and only identified one potentially efficacious subgroup within these two large clinical trials.

PMID: 28753643 [PubMed - in process]

Routine use of clinical exome-based next-generation sequencing for evaluation of patients with thrombotic microangiopathies.

Mod Pathol. 2017 Jul 28;:

Authors: Gaut JP, Jain S, Pfeifer JD, Vigh-Conrad KA, Corliss M, Sharma MK, Heusel JW, Cottrell CE

Abstract
Next-generation sequencing is increasingly used for clinical evaluation of patients presenting with thrombotic microangiopathies because it allows for simultaneous interrogation of multiple complement and coagulation pathway genes known to be associated with disease. However, the diagnostic yield is undefined in routine clinical practice. Historic studies relied on case-control cohorts, did not apply current guidelines for variant pathogenicity assessment, and used targeted gene enrichment combined with next-generation sequencing. A clinically enhanced exome, targeting ~54 Mb, was sequenced for 73 patients. Variant analysis and interpretation were performed on genes with biological relevance in thrombotic microangiopathy (C3,CD46, CFB, CFH, CFI, DGKE, and THBD). CFHR3-CFHR1 deletion status was also assessed using multiplex ligation-dependent probe amplification. Variants were classified using American College of Medical Genetics and Genomics guidelines. We identified 5 unique novel and 14 unique rare variants in 25% (18/73) of patients, including a total of 5 pathogenic, 4 likely pathogenic, and 15 variants of uncertain clinical significance. Nine patients had homozygous deletions in CFHR3-CFHR1. The diagnostic yield, defined as the presence of a pathogenic variant, likely pathogenic variant or homozygous deletion of CFHR3-CFHR1, was 25% for all patients tested. Variants of uncertain clinical significance were identified in 21% (15/73) of patients.These results illustrate the expected diagnositic yield in the setting of thrombotic microangiopathies through the application of standardized variant interpretation, and highlight the utility of such an approach. Sequencing a clinically enhanced exome to enable targeted, disease-specific variant analysis is a viable approach. The moderate rate of variants of uncertain clinical significance highlights the paucity of data surrounding the variants in our cohort and illustrates the need for expanded variant curation resources to aid in thrombotic microangiopathy-related disease variant classification.Modern Pathology advance online publication, 28 July 2017; doi:10.1038/modpathol.2017.90.

PMID: 28752844 [PubMed - as supplied by publisher]

A novel in vivo model for studying conditional dual loss of BLIMP-1 and p53 in B-cells, leading to tumor transformation.

Am J Hematol. 2017 Aug;92(8):E138-E145

Authors: Sacco A, Kawano Y, Moschetta M, Zavidij O, Huynh D, Reagan M, Mishima Y, Manier S, Park J, Morgan E, Takagi S, Wong KK, Carrasco R, Ghobrial IM, Roccaro AM

Abstract
The tumor suppressors B-lymphocyte-induced maturation protein-1 (BLIMP-1) and p53 play a crucial role in B-cell lymphomas, and their inactivation contributes to the pathogenesis of a wide spectrum of lymphoid malignancies, including diffuse large B-cell lymphomas (DLBCLs). Patients with activated B-cell-like (ABC) DLBCL may present with loss of BLIMP-1, c-Myc over-expression, decreased p53, and poor prognosis. Nevertheless, there is a lack of in vivo models recapitulating the biology of high-grade ABC DLBCL. We therefore aimed to develop an in vivo model aiming to recapitulate the phenotype observed in this cohort of patients. A Cre-Lox approach was used to achieve inactivation of both p53 and BLIMP-1 in murine B-cells. Contextual ablation of BLIMP-1 and p53 led to development of IgM-positive B-cell lymphoma with an aggressive phenotype, supported by c-Myc up-regulation, and accumulation of somatic mutations, as demonstrated by whole exome sequencing. Sensitivity of B-tumor cells to BTK inhibition was demonstrated. This model mirrors what reported in patients with ABC DLBLC, and therefore represents a novel model for studying the biology of ABC-DLBCL harboring the dual loss of BLIMP-1/p53 and c-Myc over-expression.

PMID: 28474779 [PubMed - indexed for MEDLINE]

Molecular autopsy in maternal-fetal medicine.

Genet Med. 2017 Jul 27;:

Authors: Shamseldin HE, Kurdi W, Almusafri F, Alnemer M, Alkaff A, Babay Z, Alhashem A, Tulbah M, Alsahan N, Khan R, Sallout B, Al Mardawi E, Seidahmed MZ, Meriki N, Alsaber Y, Qari A, Khalifa O, Eyaid W, Rahbeeni Z, Kurdi A, Hashem M, Alshidi T, Al-Obeid E, Abdulwahab F, Ibrahim N, Ewida N, El-Akouri K, Al Mulla M, Ben-Omran T, Pergande M, Cirak S, Al Tala S, Shaheen R, Faqeih E, Alkuraya FS

Abstract
PurposeThe application of genomic sequencing to investigate unexplained death during early human development, a form of lethality likely enriched for severe Mendelian disorders, has been limited.MethodsIn this study, we employed exome sequencing as a molecular autopsy tool in a cohort of 44 families with at least one death or lethal fetal malformation at any stage of in utero development. Where no DNA was available from the fetus, we performed molecular autopsy by proxy, i.e., through parental testing.ResultsPathogenic or likely pathogenic variants were identified in 22 families (50%), and variants of unknown significance were identified in further 15 families (34%). These variants were in genes known to cause embryonic or perinatal lethality (ALPL, GUSB, SLC17A5, MRPS16, THSD1, PIEZO1, and CTSA), genes known to cause Mendelian phenotypes that do not typically include embryonic lethality (INVS, FKTN, MYBPC3, COL11A2, KRIT1, ASCC1, NEB, LZTR1, TTC21B, AGT, KLHL41, GFPT1, and WDR81) and genes with no established links to human disease that we propose as novel candidates supported by embryonic lethality of their orthologs or other lines of evidence (MS4A7, SERPINA11, FCRL4, MYBPHL, PRPF19, VPS13D, KIAA1109, MOCS3, SVOPL, FEN1, HSPB11, KIF19, and EXOC3L2).ConclusionOur results suggest that molecular autopsy in pregnancy losses is a practical and high-yield alternative to traditional autopsy, and an opportunity for bringing precision medicine to the clinical practice of perinatology.GENETICS in MEDICINE advance online publication, 27 July 2017; doi:10.1038/gim.2017.111.

PMID: 28749478 [PubMed - as supplied by publisher]

The wide genetic landscape of clinical frontotemporal dementia: systematic combined sequencing of 121 consecutive subjects.

Genet Med. 2017 Jul 27;:

Authors: Blauwendraat C, Wilke C, Simón-Sánchez J, Jansen IE, Reifschneider A, Capell A, Haass C, Castillo-Lizardo M, Biskup S, Maetzler W, Rizzu P, Heutink P, Synofzik M

Abstract
PurposeTo define the genetic spectrum and relative gene frequencies underlying clinical frontotemporal dementia (FTD).MethodsWe investigated the frequencies and mutations in neurodegenerative disease genes in 121 consecutive FTD subjects using an unbiased, combined sequencing approach, complemented by cerebrospinal fluid Aβ1-42 and serum progranulin measurements. Subjects were screened for C9orf72 repeat expansions, GRN and MAPT mutations, and, if negative, mutations in other neurodegenerative disease genes, by whole-exome sequencing (WES) (n = 108), including WES-based copy-number variant (CNV) analysis.ResultsPathogenic and likely pathogenic mutations were identified in 19% of the subjects, including mutations in C9orf72 (n = 8), GRN (n = 7, one 11-exon macro-deletion) and, more rarely, CHCHD10, TARDBP, SQSTM1 and UBQLN2 (each n = 1), but not in MAPT or TBK1. WES also unraveled pathogenic mutations in genes not commonly linked to FTD, including mutations in Alzheimer (PSEN1, PSEN2), lysosomal (CTSF, 7-exon macro-deletion) and cholesterol homeostasis pathways (CYP27A1).ConclusionOur unbiased approach reveals a wide genetic spectrum underlying clinical FTD, including 11% of seemingly sporadic FTD. It unravels several mutations and CNVs in genes and pathways hitherto not linked to FTD. This suggests that clinical FTD might be the converging downstream result of a delicate susceptibility of frontotemporal brain networks to insults in various pathways.Genetics in Medicine advance online publication, 27 July 2017; doi:10.1038/gim.2017.102.

PMID: 28749476 [PubMed - as supplied by publisher]

PLS3 sequencing in childhood-onset primary osteoporosis identifies two novel disease-causing variants.

Osteoporos Int. 2017 Jul 26;:

Authors: Kämpe AJ, Costantini A, Mäkitie RE, Jäntti N, Valta H, Mäyränpää M, Kröger H, Pekkinen M, Taylan F, Jiao H, Mäkitie O

Abstract
Altogether 95 children with primary bone fragility were screened for variants in PLS3, the gene underlying X-linked osteoporosis. Two children with multiple peripheral and spinal fractures and low BMD had novel disease-causing PLS3 variants. Children with milder phenotypes had no pathogenic variants. PLS3 screening is indicated in childhood-onset primary osteoporosis.
INTRODUCTION: The study aimed to determine the role of pathogenic PLS3 variants in children's bone fragility and to elucidate the associated phenotypic features.
METHODS: Two cohorts of children with bone fragility were screened for variants in PLS3, the gene underlying X-linked osteoporosis. Cohort I comprised 31 patients with childhood-onset primary osteoporosis of unknown etiology. Cohort II comprised 64 children who had sustained multiple fractures but were otherwise healthy. Clinical and radiological data were reviewed. Peripheral blood DNA was Sanger sequenced for coding exons and flanking intronic regions of PLS3.
RESULTS: In two patients of cohort I, where other common genetic causes had been excluded, we identified two novel disease-causing PLS3 variants. Patient 1 was a male with bilateral femoral fractures at 10 years, low BMD (Z-score -4.1; 18 years), and multiple vertebral compression fractures. He had a novel nonsense variant in PLS3. Patient 2 was a girl with multiple long bone and vertebral fractures and low BMD (Z-score -6.6 at 6 years). She had a de novo missense variant in PLS3; whole exome sequencing and array-CGH identified no other genetic causes. Iliac crest bone biopsies confirmed low-turnover osteoporosis in both patients. In cohort II, no pathogenic PLS3 variants were identified in any of the subjects.
CONCLUSIONS: Two novel disease-causing variants in PLS3 were identified in a boy and a girl with multiple peripheral and spinal fractures and very low BMD while no pathogenic variants were identified in children with less severe skeletal fragility. PLS3 screening is warranted in male and female patients with childhood-onset primary osteoporosis.

PMID: 28748388 [PubMed - as supplied by publisher]

Lethal digenic mutations in the K(+) channels Kir4.1 (KCNJ10) and SLACK (KCNT1) associated with severe-disabling seizures and neurodevelopmental delay.

J Neurophysiol. 2017 Jul 26;:jn.00284.2017

Authors: Hasan SM, Balobaid A, Grottesi A, Dabbagh O, Cenciarini M, Rawashdeh R, Al-Sagheir A, Bove C, Macchioni L, Pessia M, Al-Owain M, D'Adamo MC

Abstract
A 2-year-old boy presented profound developmental delay, failure to thrive, ataxia, hypotonia and tonic-clonic seizures that caused the death of the patient. Targeted and whole-exome sequencing revealed two heterozygous missense variants: a novel mutation in KCNJ10 gene that encodes for the inwardly-rectifying K(+) channel Kir4.1 and another previously characterized mutation in KCNT1 that encodes for the Na(+)-activated K(+) channel known as Slo2.2 or SLACK. The objectives of this study were to perform the clinical and genetic characterization of the proband and his family and to examine the functional consequence of the Kir4.1 mutation. The mutant and wild-type KCNJ10 constructs were generated and heterologously expressed in Xenopus laevis oocytes, and whole-cell K(+) currents were measured using the two-electrode voltage-clamp technique. The KCNJ10 mutation c.652C>T resulted in a p.L218F substitution at a highly conserved residue site. Wild-type KCNJ10 expression yielded robust Kir currents, while currents from oocytes expressing the mutation were reduced. Western Blot analysis revealed reduced protein expression by the mutation. Kir5.1 subunits display selective heteromultimerization with Kir4.1 constituting channels with unique kinetics. The effect of the mutation on Kir4.1/5.1 channel activity was twofold: a reduction in current amplitudes and an increase in the pH-dependent inhibition. We thus report a novel loss-of-function mutation in Kir4.1 found in a patient with a co-exiting mutation in SLACK channels that results in a fatal disease.

PMID: 28747464 [PubMed - as supplied by publisher]

International Cooperation to Enable the Diagnosis of All Rare Genetic Diseases.

Am J Hum Genet. 2017 May 04;100(5):695-705

Authors: Boycott KM, Rath A, Chong JX, Hartley T, Alkuraya FS, Baynam G, Brookes AJ, Brudno M, Carracedo A, den Dunnen JT, Dyke SOM, Estivill X, Goldblatt J, Gonthier C, Groft SC, Gut I, Hamosh A, Hieter P, Höhn S, Hurles ME, Kaufmann P, Knoppers BM, Krischer JP, Macek M, Matthijs G, Olry A, Parker S, Paschall J, Philippakis AA, Rehm HL, Robinson PN, Sham PC, Stefanov R, Taruscio D, Unni D, Vanstone MR, Zhang F, Brunner H, Bamshad MJ, Lochmüller H

Abstract
Provision of a molecularly confirmed diagnosis in a timely manner for children and adults with rare genetic diseases shortens their "diagnostic odyssey," improves disease management, and fosters genetic counseling with respect to recurrence risks while assuring reproductive choices. In a general clinical genetics setting, the current diagnostic rate is approximately 50%, but for those who do not receive a molecular diagnosis after the initial genetics evaluation, that rate is much lower. Diagnostic success for these more challenging affected individuals depends to a large extent on progress in the discovery of genes associated with, and mechanisms underlying, rare diseases. Thus, continued research is required for moving toward a more complete catalog of disease-related genes and variants. The International Rare Diseases Research Consortium (IRDiRC) was established in 2011 to bring together researchers and organizations invested in rare disease research to develop a means of achieving molecular diagnosis for all rare diseases. Here, we review the current and future bottlenecks to gene discovery and suggest strategies for enabling progress in this regard. Each successful discovery will define potential diagnostic, preventive, and therapeutic opportunities for the corresponding rare disease, enabling precision medicine for this patient population.

PMID: 28475856 [PubMed - indexed for MEDLINE]

De Novo Coding Variants Are Strongly Associated with Tourette Disorder.

Neuron. 2017 May 03;94(3):486-499.e9

Authors: Willsey AJ, Fernandez TV, Yu D, King RA, Dietrich A, Xing J, Sanders SJ, Mandell JD, Huang AY, Richer P, Smith L, Dong S, Samocha KE, Tourette International Collaborative Genetics (TIC Genetics), Tourette Syndrome Association International Consortium for Genetics (TSAICG), Neale BM, Coppola G, Mathews CA, Tischfield JA, Scharf JM, State MW, Heiman GA

Abstract
Whole-exome sequencing (WES) and de novo variant detection have proven a powerful approach to gene discovery in complex neurodevelopmental disorders. We have completed WES of 325 Tourette disorder trios from the Tourette International Collaborative Genetics cohort and a replication sample of 186 trios from the Tourette Syndrome Association International Consortium on Genetics (511 total). We observe strong and consistent evidence for the contribution of de novo likely gene-disrupting (LGD) variants (rate ratio [RR] 2.32, p = 0.002). Additionally, de novo damaging variants (LGD and probably damaging missense) are overrepresented in probands (RR 1.37, p = 0.003). We identify four likely risk genes with multiple de novo damaging variants in unrelated probands: WWC1 (WW and C2 domain containing 1), CELSR3 (Cadherin EGF LAG seven-pass G-type receptor 3), NIPBL (Nipped-B-like), and FN1 (fibronectin 1). Overall, we estimate that de novo damaging variants in approximately 400 genes contribute risk in 12% of clinical cases. VIDEO ABSTRACT.

PMID: 28472652 [PubMed - indexed for MEDLINE]

Whole exome sequencing unveils a frameshift mutation in CNGB3 for cone dystrophy: A case report of an Indian family.

Medicine (Baltimore). 2017 Jul;96(30):e7490

Authors: Gupta S, Chaurasia A, Pathak E, Mishra R, Chaudhry VN, Chaudhry P, Mukherjee A, Mutsuddi M

Abstract
RATIONALE: Genetic elucidation of cone-dominated retinal dystrophies in Indian subcontinent is much needed to identify and catalog underlying genetic defects. In this context, the present study recruited a consanguineous Indian family affected with autosomal recessive cone dystrophy (CD). Considering the huge genetic heterogeneity and recessive inheritance of the disease, we chose to dissect out causal variant in this family by whole exome sequencing (WES).
PATIENT CONCERNS: In the recruited family, three of the six siblings had complaints of poor visual acuity, photophobia, and disturbed colour vision since early childhood. Fundus examination disclosed vascular attenuation and macular retinal pigment epithelium (RPE) changes in all the affected siblings, signifying degeneration of photoreceptor cells.
DIAGNOSIS: Complete clinical investigation and electroretinography studies led to the diagnosis of cone dystrophy in three siblings of the family.
INTERVENTIONS: Detailed ophthalmic examination, including family history, visual function testing, and retinal imaging, was performed. We captured and sequenced exomes of 2 affected siblings and their mother using SureSelect Human All Exon V5 Kit on Illumina HiSeq 2000/2500 platform with 100 bp paired-end sequencing method. Candidates after data analysis were screened by segregation analysis and Sanger sequencing. Considering recessive inheritance and consanguinity in the pedigree, we attempted to map large loci homozygous by descent in the genome of patients using exome sequencing variants. Extensive protein modeling was carried out to assess possible consequences of the identified variant on the 3-dimensional structure of the protein.
OUTCOMES: WES generated more than 65,000 variants for each individual. Assuming recessive inheritance, 13,026 variants were selected. Further filtering on the basis of their position in gene, class, and minor allele frequency constricted the huge list to 12 rare variants. Finally, we ascertained a single base deletion c.1148delC (p.Thr383fs) in the gene CNGB3 as the causal variant. This is a recurrent frameshift mutation resulting in truncated CNGB3 protein. We mapped a large 15-Mb stretch of homozygous markers spanning the causal variant in the proband. The gene CNGB3 encodes modulatory subunit of cyclic nucleotide-gated channels in cone photoreceptors. Protein modeling reveals loss of 2 transmembrane helices and conserved CAP_ED domain in truncated CNGB3, which eventually is predicted to form nonfunctional channels and hamper phototransduction.
LESSONS: We have identified a recurrent mutation c.1148delC (p.Thr383fs) in CNGB3 for autosomal recessive CD. The present report provides the first description of CNGB3 mutation from India. It is also the foremost investigation of familial CD in Indian patients; therefore, it presents the primary genetic etiology of CD in India.

PMID: 28746191 [PubMed - in process]

Whole-exome sequencing of Finnish hereditary breast cancer families.

Eur J Hum Genet. 2016 Jan;25(1):85-93

Authors: Määttä K, Rantapero T, Lindström A, Nykter M, Kankuri-Tammilehto M, Laasanen SL, Schleutker J

Abstract
A remarkable proportion of factors causing genetic predisposition to breast cancer (BC) are unknown in non-BRCA1/2 families. Exome sequencing was performed for 13 high-risk Finnish hereditary breast and/or ovarian cancer (HBOC) families to detect variants contributing to BC susceptibility. After filtering, 18 candidate variants in DNA damage response (DDR) pathway genes were screened in 129 female HBOC patients, up to 989 female controls, and 31 breast tumours by Sanger sequencing/TaqMan assays. In addition, two variants were further studied in 49 male BC patients and 909 male controls. Second, all variants predicted to affect function in six early-onset BC patients were analysed in detail. Variants in ATM, MYC, PLAU, RAD1, and RRM2B were enriched in female HBOC patients compared with controls (odds ratio 1.16-2.16). A rare nonsynonymous variant in RAD50 was detected in a male BC patient. In addition, a very rare BRCA1 variant was identified in a single high-risk family. None of the variants showed wild-type allele loss in breast tumours. Furthermore, novel variants predicted to affect function were detected in early-onset patients in genes, which target DNA repair and replication, signalling, apoptosis, and cell cycle pathways. Family-specific enrichment of multiple DDR pathway gene defects likely explains BC predisposition in the studied families. These findings provide new information on potential BC-related pathways and an excellent premise for future studies.

PMID: 27782108 [PubMed - indexed for MEDLINE]

A genotypic ascertainment approach to refute the association of MYO1A variants with non-syndromic deafness.

Eur J Hum Genet. 2016 Jan;25(1):147-149

Authors: Patton J, Brewer C, Chien W, Johnston JJ, Griffith AJ, Biesecker LG

Abstract
Variants in the unconventional myosin gene, MYO1A, have been reported to cause non-syndromic sensorineural hearing loss with a pattern of autosomal dominant inheritance. Others have challenged this association. We used a genotypic ascertainment study design to test the association of MYO1A variants with hearing loss. We evaluated MYO1A variants from a cohort of 951 individuals with exome sequencing who were not ascertained for hearing loss. Five individuals had one of two variants claimed to be associated with sensorineural hearing loss in a prior study and 33 individuals had one of 13 predicted deleterious variants. We obtained audiology evaluations for 12 individuals with these variants of interest. The hearing acuity of the participants was compared with age- and sex-matched controls and published age- and sex-specific reference ranges from a large population of otologically screened adults. None of the participants had bilateral sensorineural hearing loss of moderate or greater severity. These data do not support a causal relationship of variants in MYO1A to sensorineural hearing loss. We suggest that the genotypic ascertainment method is useful to objectively evaluate gene-phenotype associations.

PMID: 27759032 [PubMed - indexed for MEDLINE]

Variants in SKP1, PROB1, and IL17B genes at keratoconus 5q31.1-q35.3 susceptibility locus identified by whole-exome sequencing.

Eur J Hum Genet. 2016 Jan;25(1):73-78

Authors: Karolak JA, Gambin T, Pitarque JA, Molinari A, Jhangiani S, Stankiewicz P, Lupski JR, Gajecka M

Abstract
Keratoconus (KTCN) is a protrusion and thinning of the cornea, resulting in impairment of visual function. The extreme genetic heterogeneity makes it difficult to discover factors unambiguously influencing the KTCN phenotype. In this study, we used whole-exome sequencing (WES) and Sanger sequencing to reduce the number of candidate genes at the 5q31.1-q35.3 locus and to prioritize other potentially relevant variants in an Ecuadorian family with KTCN. We applied WES in two affected KTCN individuals from the Ecuadorian family that showed a suggestive linkage between the KTCN phenotype and the 5q31.1-q35.3 locus. Putative variants identified by WES were further evaluated in this family using Sanger sequencing. Exome capture discovered a total of 173 rare (minor allele frequency <0.001 in control population) nonsynonymous variants in both affected individuals. Among them, 16 SNVs were selected for further evaluation. Segregation analysis revealed that variants c.475T>G in SKP1, c.671G>A in PROB1, and c.527G>A in IL17B in the 5q31.1-q35.3 linkage region, and c.850G>A in HKDC1 in the 10q22 locus completely segregated with the phenotype in the studied KTCN family. We demonstrate that a combination of various techniques significantly narrowed the studied genomic region and reduced the list of the putative exonic variants. Moreover, since this locus overlapped two other chromosomal regions previously recognized in distinct KTCN studies, our findings suggest that this 5q31.1-q35.3 locus might be linked with KTCN.

PMID: 27703147 [PubMed - indexed for MEDLINE]

Congenital protein losing enteropathy: an inborn error of lipid metabolism due to DGAT1 mutations.

Eur J Hum Genet. 2016 Aug;24(9):1268-73

Authors: Stephen J, Vilboux T, Haberman Y, Pri-Chen H, Pode-Shakked B, Mazaheri S, Marek-Yagel D, Barel O, Di Segni A, Eyal E, Hout-Siloni G, Lahad A, Shalem T, Rechavi G, Malicdan MC, Weiss B, Gahl WA, Anikster Y

Abstract
Protein-losing enteropathy (PLE) is a clinical disorder of protein loss from the gastrointestinal system that results in hypoproteinemia and malnutrition. This condition is associated with a wide range of gastrointestinal disorders. Recently, a unique syndrome of congenital PLE associated with biallelic mutations in the DGAT1 gene has been reported in a single family. We hypothesize that mutations in this gene are responsible for undiagnosed cases of PLE in infancy. Here we investigated three children in two families presenting with severe diarrhea, hypoalbuminemia and PLE, using clinical studies, homozygosity mapping, and exome sequencing. In one family, homozygosity mapping using SNP arrays revealed the DGAT1 gene as the best candidate gene for the proband. Sequencing of all the exons including flanking regions and promoter regions of the gene identified a novel homozygous missense variant, p.(Leu295Pro), in the highly conserved membrane-bound O-acyl transferase (MBOAT) domain of the DGAT1 protein. Expression studies verified reduced amounts of DGAT1 in patient fibroblasts. In a second family, exome sequencing identified a previously reported splice site mutation in intron 8. These cases of DGAT1 deficiency extend the molecular and phenotypic spectrum of PLE, suggesting a re-evaluation of the use of DGAT1 inhibitors for metabolic disorders including obesity and diabetes.

PMID: 26883093 [PubMed - indexed for MEDLINE]