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Exome sequencing has markedly enhanced the discovery of genes implicated in Mendelian disorders, particularly for individuals in whom a known clinical entity could not be assigned. This has led to the recognition that phenotypic heterogeneity resulting from allelic mutations occurs more commonly than previously appreciated. Here, we report that missense variants in CDC42, a gene encoding a small GTPase functioning as an intracellular signaling node, underlie a clinically heterogeneous group of phenotypes characterized by variable growth dysregulation, facial dysmorphism, and neurodevelopmental, immunological, and hematological anomalies, including a phenotype resembling Noonan syndrome, a developmental disorder caused by dysregulated RAS signaling. In silico, in vitro, and in vivo analyses demonstrate that mutations variably perturb CDC42 function by altering the switch between the active and inactive states of the GTPase and/or affecting CDC42 interaction with effectors, and differentially disturb cellular and developmental processes. These findings reveal the remarkably variable impact that dominantly acting CDC42 mutations have on cell function and development, creating challenges in syndrome definition, and exemplify the importance of functional profiling for syndrome recognition and delineation., (Copyright © 2017 American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

Background: With the expanded availability of next generation sequencing (NGS)-based clinical genetic tests, clinicians seeking to test patients with Mendelian diseases must weigh the superior coverage of targeted gene panels with the greater number of genes included in whole exome sequencing (WES) when considering their first-tier testing approach. Here, we use an in silico analysis to predict the analytic sensitivity of WES using pathogenic variants identified on targeted NGS panels as a reference., Methods: Corresponding nucleotide positions for 1533 different alterations classified as pathogenic or likely pathogenic identified on targeted NGS multi-gene panel tests in our laboratory were interrogated in data from 100 randomly-selected clinical WES samples to quantify the sequence coverage at each position. Pathogenic variants represented 91 genes implicated in hereditary cancer, X-linked intellectual disability, primary ciliary dyskinesia, Marfan syndrome/aortic aneurysms, cardiomyopathies and arrhythmias., Results: When assessing coverage among 100 individual WES samples for each pathogenic variant (153,300 individual assessments), 99.7% (n = 152,798) would likely have been detected on WES. All pathogenic variants had at least some coverage on exome sequencing, with a total of 97.3% (n = 1491) detectable across all 100 individuals. For the remaining 42 pathogenic variants, the number of WES samples with adequate coverage ranged from 35 to 99. Factors such as location in GC-rich, repetitive, or homologous regions likely explain why some of these alterations were not detected across all samples. To validate study findings, a similar analysis was performed against coverage data from 60,706 exomes available through the Exome Aggregation Consortium (ExAC). Results from this validation confirmed that 98.6% (91,743,296/93,062,298) of pathogenic variants demonstrated adequate depth for detection., Conclusions: Results from this in silico analysis suggest that exome sequencing may achieve a diagnostic yield similar to panel-based testing for Mendelian diseases., Competing Interests: All authors were full time paid employees of Ambry Genetics at the time the study was conducted. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Diagnostic exome sequencing (DES) is an effective tool for diagnosis in intractable cases where the underlying cause is thought be genetic. It is commonly assumed that patients with a family history of consanguinity will have increased detection rates for rare autosomal recessive Mendelian disorders through DES. Herein, we analyzed the diagnostic yield and relevant inheritance patterns within the DES cases with a reported consanguineous family history. Of the first 500 unselected cases referred for DES, 40 (8.0%) had a known consanguineous family history. Among the 40 cases, 13 (32.5%) received a definitive molecular diagnosis through DES and such positive rate is similar to that of families with no reported consanguinity (139/460, 30.2%, P=0.63). Although homozygous alterations likely related to consanguinity have been identified in eight positive cases, the other five (38.4%) causative mutations were unrelated to autosomal recessive inheritance. Our retrospective analysis demonstrated that individuals with known consanguinity were not more likely to have a positive DES result and a significant portion of the positive findings were not within an autosomal recessive gene. These results highlight that all applicable inheritance patterns should be considered for patients with a known family history of consanguinity.

Background: Large-scale cohort-based whole exome sequencing of individuals with neurodevelopmental disorders (NDDs) has identified numerous novel candidate disease genes; however, detailed phenotypic information is often lacking in such studies. De novo mutations in pogo transposable element with zinc finger domain (POGZ) have been identified in six independent and diverse cohorts of individuals with NDDs ranging from autism spectrum disorder to developmental delay., Methods: Whole exome sequencing was performed on five unrelated individuals. Sanger sequencing was used to validate variants and segregate mutations with the phenotype in available family members., Results: We identified heterozygous truncating mutations in POGZ in five unrelated individuals, which were confirmed to be de novo or not present in available parental samples. Careful review of the phenotypes revealed shared features that included developmental delay, intellectual disability, hypotonia, behavioral abnormalities, and similar facial characteristics. Variable features included short stature, microcephaly, strabismus and hearing loss., Conclusions: While POGZ has been associated with neurodevelopmental disorders in large cohort studies, our data suggest that loss of function variants in POGZ lead to an identifiable syndrome of NDD with specific phenotypic traits. This study exemplifies the era of human reverse clinical genomics ushered in by large disease-directed cohort studies; first defining a new syndrome molecularly and, only subsequently, phenotypically.

Heritable connective tissue diseases are a highly heterogeneous family of over 200 disorders that affect the extracellular matrix. While the genetic basis of several disorders is established, the etiology has not been discovered for a large portion of patients, likely due to rare yet undiscovered disease genes. By performing trio-exome sequencing of a 55-year-old male proband presenting with multiple symptoms indicative of a connective disorder, we identified a heterozygous missense alteration in exon 1 of the Elastin Microfibril Interfacer 1 (EMILIN1) gene, c.64G>A (p.A22T). The proband presented with ascending and descending aortic aneurysms, bilateral lower leg and foot sensorimotor peripheral neuropathy, arthropathy, and increased skin elasticity. Sanger sequencing confirmed that the EMILIN1 alteration, which maps around the signal peptide cleavage site, segregated with disease in the affected proband, mother, and son. The impaired secretion of EMILIN-1 in cells transfected with the mutant p.A22T coincided with abnormal protein accumulation within the endoplasmic reticulum. In skin biopsy of the proband, we detected less EMILIN-1 with disorganized and abnormal coarse fibrils, aggregated deposits underneath the epidermis basal lamina, and dermal cells apoptosis. These findings collectively suggest that EMILIN1 may represent a new disease gene associated with an autosomal-dominant connective tissue disorder., (© 2015 The Authors. **Human Mutation published by Wiley Periodicals, Inc.)

Purpose: Diagnostic exome sequencing was immediately successful in diagnosing patients in whom traditional technologies were uninformative. Herein, we provide the results from the first 500 probands referred to a clinical laboratory for diagnostic exome sequencing., Methods: Family-based exome sequencing included whole-exome sequencing followed by family inheritance-based model filtering, comprehensive medical review, familial cosegregation analysis, and analysis of novel genes., Results: A positive or likely positive result in a characterized gene was identified in 30% of patients (152/500). A novel gene finding was identified in 7.5% of patients (31/416). The highest diagnostic rates were observed among patients with ataxia, multiple congenital anomalies, and epilepsy (44, 36, and 35%, respectively). Twenty-three percent of positive findings were within genes characterized within the past 2 years. The diagnostic rate was significantly higher among families undergoing a trio (37%) as compared with a singleton (21%) whole-exome testing strategy., Conclusion: Overall, we present results from the largest clinical cohort of diagnostic exome sequencing cases to date. These data demonstrate the utility of family-based exome sequencing and analysis to obtain the highest reported detection rate in an unselected clinical cohort, illustrating the utility of diagnostic exome sequencing as a transformative technology for the molecular diagnosis of genetic disease.

Elongator is a multi-subunit protein complex essential to transcription elongation, histone acetylation, and tRNA modification. The complex consists of six highly conserved protein subunits, called Elongator Proteins (ELP) 1-6. Apart from an association with intellectual disability (ID), there is limited clinical information about patients with ELP2 variants. Here we report on two brothers with severe ID, spastic diplegia, and self-injury whose presentation eluded a diagnosis for over 20 years. In both brothers, whole exome sequencing revealed a likely pathogenic, compound heterozygous missense variant in ELP2. We describe the phenotype and natural history of the ELP2-related disorder in these brothers., (© 2015 Wiley Periodicals, Inc.)

Purpose: Exome sequencing of a single individual for a clinical indication may result in the identification of incidental deleterious variants unrelated to the indication for testing (secondary findings). Given the recent availability of clinical exome testing, there is a limited knowledge regarding the disclosure preferences and impact of secondary findings in a clinical diagnostic setting. In this article, we provide preliminary data regarding the preferences for secondary findings results disclosure based on the first 200 families referred to Ambry Genetics for diagnostic exome sequencing., Methods: Secondary findings were categorized into four groups in the diagnostic exome sequencing consent: carrier status of recessive disorders, predisposition to later-onset disease, predisposition to increased cancer risk, and early-onset disease. In this study, we performed a retrospective analysis of patient responses regarding the preferences for secondary findings disclosure., Results: The majority of patients (187/200; 93.5%) chose to receive secondary results for one or more available categories. Adult probands were more likely than children to opt for blinding of secondary data (16 vs. 4%, respectively). Among responses for blinding, preferences were evenly scattered among categories., Conclusion: These data represent the unprecedented results of a large reference laboratory providing clinical exome sequencing. We report, for the first time, the preferences of patients and families for the receipt of secondary findings based on clinical genome sequencing. Overwhelmingly, families undergoing exome sequencing opt for the disclosure of secondary findings. The data may have implications regarding the development of guidelines for secondary findings reporting among patients with severe and/or life-threatening disease undergoing clinical genomic sequencing.

Analysis of spontaneous multiple mutations in normal and tumor cells may constrain hypotheses about the mechanisms responsible for multiple mutations and provide insight into the mutator phenotype. In a previous study, spontaneous doublets in Big Blue mice were dramatically more frequent than expected by chance and exhibited a mutation pattern similar to that observed for single mutations [Mutat. Res. 452 (2000) 219]. The spacing between mutations in doublets was generally closer than expected by chance and the distribution of mutation spacing fit an exponential, albeit with substantial scatter. We now analyze 2658 additional mutants and confirm that doublets are enhanced dramatically relative to chance expectation. The spacing, frequency and pattern of spontaneous doublets and multiplets (domuplets) are examined as a function of age, tissue type, p53-deficiency and neoplasia in the new and combined data. The new and combined data confirm that the distribution of the spacing between mutations in doublets is non-random with the mutations more closely spaced than expected by chance (P < 0.0005; combined data), consistent with temporally coordinate (chronocoordinate) events. An exponential provides an excellent fit to the distribution (R2 = 0.98) and estimates that half of doublets have mutations separated by 120 nucleotides or less (the "half-life of mutation spacing"). We make several novel observations: (i) singlets and doublets show similar overall increases in frequency with age (ii) doublet frequency may be lower in the male germline, consistent with the generally reduced mutation frequency in the male germline (iii) doublet frequencies are elevated in somatic tissues of p53-deficient mice (Li-Fraumini cancer syndrome model; P = 0.005) and (iv) doublets and singlets in tumors from p53-deficient mice have a different mutation pattern (P = 0.007). The observations are consistent with chronocoordinate occurrence of spontaneous doublets and multiplets due to a transient error-prone condition and do not suggest a major role for the recently discovered Y family of error-prone polymerases. The enhancement of doublets in p53-deficient mice may contribute to cancer risk.

To supplement a previous analysis of spontaneous tandem-base mutations (TBM) in the lacI gene of Big Blue((R)) mice, 2658 additional mutants were sequenced from 13 tissues and 44 spontaneous TBM were identified (tripling the sample size). Previous findings were confirmed and generalized and several new observations were made. TBM differ from single and other double mutations in that TBM frequency varies dramatically with tissue type. In certain tissues, most notably male germ cells, no TBM are observed despite screening as many as 26 million plaque forming units. TBM are most frequent in kidney and liver (3.45 and 2x10(-6), respectively), accounting for 7.6 and 4.8% of all mutational events in kidney and liver, respectively. There is a trend for elevated TBM frequency in thymic lymphomas in p53-deficient mice. TBM are more frequent in old age in both liver and kidney. TBM differ from single mutations and other double mutations because they display a marked difference in pattern and dramatic tissue specificity for target sequence. Five of the 78 possible TBM outcomes comprise 79% of those observed, and mutations at GG/CC predominate. TBM in mice were compared with TBM found in human mutation databases. TBM are also rare in the human germline (one in 5133 germline mutations reported in five human mutation databases). In general, the types of somatic TBM are similar in mice and humans except for an excess of TG/CA to CA/TG TBM in humans (TBM related to ultraviolet light-induced skin cancer were excluded). TBM may be the result of unknown mechanisms that may have some similarities in mice and humans.

Amyotrophic lateral sclerosis (ALS) is a progressive paralytic disorder caused by motor neuron degeneration. A similar disease phenotype is observed in mice overexpressing a mutant human hSOD1 gene (G93A, 1Gurd(1)). Mice transgenic for lacI (Big Blue) and human mutant (1Gurd(1), Mut hSOD1) or wild type (2Gur, Wt hSOD1) SOD1 genes were used to examine spontaneous mutation, oxidative DNA damage, and neurodegeneration in vivo. The frequency and pattern of spontaneous mutation were determined for forebrain (90% glia), cerebellum (90% neurons) and thymus from 5-month-old male mice. Mutation frequency is not elevated significantly and mutation pattern is unaltered in Mut hSOD1 mice compared to control mice. Mutation frequency is reduced significantly in the cerebellum of Wt hSOD1 mice (1.6x10(-5); P=0.0093; Fisher's Exact Test) compared to mice without a human transgene (2.7x10(-5)). Mutation pattern is unaltered. This first report of an endogenous factor that can reduce in vivo, the frequency of spontaneous mutation suggests potential strategies for lowering mutagenesis related to aging, neurodegeneration, and carcinogenesis.