Alicia Braxton

Clinical Whole-Exome Sequencing for the Diagnosis of Mendelian Disorders

BACKGROUND Whole-exome sequencing is a diagnostic approach for the identification of molecular defects in patients with suspected genetic disorders. METHODS We developed technical, bioinformatic, interpretive, and validation pipelines for whole-exome sequencing in a certified clinical laboratory to identify sequence variants underlying disease phenotypes in patients. RESULTS We present data on the first 250 probands for whom referring physicians ordered whole-exome sequencing. Patients presented with a range of phenotypes suggesting potential genetic causes. Approximately 80% were children with neurologic phenotypes. Insurance coverage was similar to that for established genetic tests. We identified 86 mutated alleles that were highly likely to be causative in 62 of the 250 patients, achieving a 25% molecular diagnostic rate (95% confidence interval, 20 to 31). Among the 62 patients, 33 had autosomal dominant disease, 16 had autosomal recessive disease, and 9 had X-linked disease. A total of 4 probands received two nonoverlapping molecular diagnoses, which potentially challenged the clinical diagnosis that had been made on the basis of history and physical examination. A total of 83% of the autosomal dominant mutant alleles and 40% of the X-linked mutant alleles occurred de novo. Recurrent clinical phenotypes occurred in patients with mutations that were highly likely to be causative in the same genes and in different genes responsible for genetically heterogeneous disorders. CONCLUSIONS Whole-exome sequencing identified the underlying genetic defect in 25% of consecutive patients referred for evaluation of a possible genetic condition. (Funded by the National Human Genome Research Institute.).

Molecular Findings Among Patients Referred for Clinical Whole-Exome Sequencing

IMPORTANCE Clinical whole-exome sequencing is increasingly used for diagnostic evaluation of patients with suspected genetic disorders. OBJECTIVE To perform clinical whole-exome sequencing and report (1) the rate of molecular diagnosis among phenotypic groups, (2) the spectrum of genetic alterations contributing to disease, and (3) the prevalence of medically actionable incidental findings such as FBN1 mutations causing Marfan syndrome. DESIGN, SETTING, AND PATIENTS Observational study of 2000 consecutive patients with clinical whole-exome sequencing analyzed between June 2012 and August 2014. Whole-exome sequencing tests were performed at a clinical genetics laboratory in the United States. Results were reported by clinical molecular geneticists certified by the American Board of Medical Genetics and Genomics. Tests were ordered by the patients physician. The patients were primarily pediatric (1756 [88%]; mean age, 6 years; 888 females [44%], 1101 males [55%], and 11 fetuses [1% gender unknown]), demonstrating diverse clinical manifestations most often including nervous system dysfunction such as developmental delay. MAIN OUTCOMES AND MEASURES Whole-exome sequencing diagnosis rate overall and by phenotypic category, mode of inheritance, spectrum of genetic events, and reporting of incidental findings. RESULTS A molecular diagnosis was reported for 504 patients (25.2%) with 58% of the diagnostic mutations not previously reported. Molecular diagnosis rates for each phenotypic category were 143/526 (27.2%; 95% CI, 23.5%-31.2%) for the neurological group, 282/1147 (24.6%; 95% CI, 22.1%-27.2%) for the neurological plus other organ systems group, 30/83 (36.1%; 95% CI, 26.1%-47.5%) for the specific neurological group, and 49/244 (20.1%; 95% CI, 15.6%-25.8%) for the nonneurological group. The Mendelian disease patterns of the 527 molecular diagnoses included 280 (53.1%) autosomal dominant, 181 (34.3%) autosomal recessive (including 5 with uniparental disomy), 65 (12.3%) X-linked, and 1 (0.2%) mitochondrial. Of 504 patients with a molecular diagnosis, 23 (4.6%) had blended phenotypes resulting from 2 single gene defects. About 30% of the positive cases harbored mutations in disease genes reported since 2011. There were 95 medically actionable incidental findings in genes unrelated to the phenotype but with immediate implications for management in 92 patients (4.6%), including 59 patients (3%) with mutations in genes recommended for reporting by the American College of Medical Genetics and Genomics. CONCLUSIONS AND RELEVANCE Whole-exome sequencing provided a potential molecular diagnosis for 25% of a large cohort of patients referred for evaluation of suspected genetic conditions, including detection of rare genetic events and new mutations contributing to disease. The yield of whole-exome sequencing may offer advantages over traditional molecular diagnostic approaches in certain patients.

Genetic Counselors’ Views and Experiences with the Clinical Integration of Genome Sequencing

In recent years, new sequencing technologies known as next generation sequencing (NGS) have provided scientists the ability to rapidly sequence all known coding as well as non-coding sequences in the human genome. As the two emerging approaches, whole exome (WES) and whole genome (WGS) sequencing, have started to be integrated in the clinical arena, we sought to survey health care professionals who are likely to be involved in the implementation process now and/or in the future (e.g., genetic counselors, geneticists and nurse practitioners). Two hundred twenty-one genetic counselors— one third of whom currently offer WES/WGS—participated in an anonymous online survey. The aims of the survey were first, to identify barriers to the implementation of WES/WGS, as perceived by survey participants; second, to provide the first systematic report of current practices regarding the integration of WES/WGS in clinic and/or research across the US and Canada and to illuminate the roles and challenges of genetic counselors participating in this process; and third to evaluate the impact of WES/WGS on patient care. Our results showed that genetic counseling practices with respect to WES/WGS are consistent with the criteria set forth in the ACMG 2012 policy statement, which highlights indications for testing, reporting, and pre/post test considerations. Our respondents described challenges related to offering WES/WGS, which included billing issues, the duration and content of the consent process, result interpretation and disclosure of incidental findings and variants of unknown significance. In addition, respondents indicated that specialty area (i.e., prenatal and cancer), lack of clinical utility of WES/WGS and concerns about interpretation of test results were factors that prevented them from offering this technology to patients. Finally, study participants identified the aspects of their professional training which have been most beneficial in aiding with the integration of WES/WGS into the clinical setting (molecular/clinical genetics, counseling and bioethics) and suggested that counseling aids (to assist them when explaining aspects of these tests to patients) and webinars focused on WES/WGS (for genetic counselors and other health care professionals) would be useful educational tools. Future research should permit us to further enhance our knowledge of pitfalls and benefits associated with the introduction of these powerful technologies in patient care and to further explore the roles and opportunities for genetic counselors in this rapidly evolving field.

Use of Exome Sequencing for Infants in Intensive Care Units: Ascertainment of Severe Single-Gene Disorders and Effect on Medical Management

Importance While congenital malformations and genetic diseases are a leading cause of early infant death, to our knowledge, the contribution of single-gene disorders in this group is undetermined. Objective To determine the diagnostic yield and use of clinical exome sequencing in critically ill infants. Design, Setting, and Participants Clinical exome sequencing was performed for 278 unrelated infants within the first 100 days of life who were admitted to Texas Children’s Hospital in Houston, Texas, during a 5-year period between December 2011 and January 2017. Exome sequencing types included proband exome, trio exome, and critical trio exome, a rapid genomic assay for seriously ill infants. Main Outcomes and Measures Indications for testing, diagnostic yield of clinical exome sequencing, turnaround time, molecular findings, patient age at diagnosis, and effect on medical management among a group of critically ill infants who were suspected to have genetic disorders. Results The mean (SEM) age for infants participating in the study was 28.5 (1.7) days; of these, the mean (SEM) age was 29.0 (2.2) days for infants undergoing proband exome sequencing, 31.5 (3.9) days for trio exome, and 22.7 (3.9) days for critical trio exome. Clinical indications for exome sequencing included a range of medical concerns. Overall, a molecular diagnosis was achieved in 102 infants (36.7%) by clinical exome sequencing, with relatively low yield for cardiovascular abnormalities. The diagnosis affected medical management for 53 infants (52.0%) and had a substantial effect on informed redirection of care, initiation of new subspecialist care, medication/dietary modifications, and furthering life-saving procedures in select patients. Critical trio exome sequencing revealed a molecular diagnosis in 32 of 63 infants (50.8%) at a mean (SEM) of 33.1 (5.6) days of life with a mean (SEM) turnaround time of 13.0 (0.4) days. Clinical care was altered by the diagnosis in 23 of 32 patients (71.9%). The diagnostic yield, patient age at diagnosis, and medical effect in the group that underwent critical trio exome sequencing were significantly different compared with the group who underwent regular exome testing. For deceased infants (n = 81), genetic disorders were molecularly diagnosed in 39 (48.1%) by exome sequencing, with implications for recurrence risk counseling. Conclusions and Relevance Exome sequencing is a powerful tool for the diagnostic evaluation of critically ill infants with suspected monogenic disorders in the neonatal and pediatric intensive care units and its use has a notable effect on clinical decision making.

Positive predictive value estimates for cell-free noninvasive prenatal screening from data of a large referral genetic diagnostic laboratory

Background Since its debut in 2011, cell‐free fetal DNA screening has undergone rapid expansion with respect to both utilization and coverage. However, conclusive data regarding the clinical validity and utility of this screening tool, both for the originally included common autosomal and sex‐chromosomal aneuploidies as well as the more recently added chromosomal microdeletion syndromes, have lagged behind. Thus, there is a continued need to educate clinicians and patients about the current benefits and limitations of this screening tool to inform pre‐ and posttest counseling, pre/perinatal decision making, and medical risk assessment/management. Objective The objective of this study was to determine the positive predictive value and false‐positive rates for different chromosomal abnormalities identified by cell‐free fetal DNA screening using a large data set of diagnostic testing results on invasive samples submitted to the laboratory for confirmatory studies. Study Design We tested 712 patient samples sent to our laboratory to confirm a cell‐free fetal DNA screening result, indicating high risk for a chromosome abnormality. We compiled data from all cases in which the indication for confirmatory testing was a positive cell‐free fetal DNA screen, including the common trisomies, sex chromosomal aneuploidies, microdeletion syndromes, and other large genome‐wide copy number abnormalities. Testing modalities included fluorescence in situ hybridization, G‐banded karyotype, and/or chromosomal microarray analysis performed on chorionic villus samples, amniotic fluid, or postnatally obtained blood samples. Positive predictive values and false‐positive rates were calculated from tabulated data. Results The positive predictive values for trisomy 13, 18, and 21 were consistent with previous reports at 45%, 76%, and 84%, respectively. For the microdeletion syndrome regions, positive predictive values ranged from 0% for detection of Cri‐du‐Chat syndrome and Prader‐Willi/Angelman syndrome to 14% for 1p36 deletion syndrome and 21% for 22q11.2 deletion syndrome. Detection of sex chromosomal aneuploidies had positive predictive values of 26% for monosomy X, 50% for 47,XXX, and 86% for 47,XXY. Conclusion The positive predictive values for detection of common autosomal and sex chromosomal aneuploidies by cell‐free fetal DNA screening were comparable with other studies. Identification of microdeletions was associated with lower positive predictive values and higher false‐positive rates, likely because of the low prevalence of the individual targeted microdeletion syndromes in the general population. Although the obtained positive predictive values compare favorably with those seen in traditional screening approaches for common aneuploidies, they highlight the importance of educating clinicians and patients on the limitations of cell‐free fetal DNA screening tests. Improvement of the cell‐free fetal DNA screening technology and continued monitoring of its performance after introduction into clinical practice will be important to fully establish its clinical utility. Nonetheless, our data provide valuable information that may aid result interpretation, patient counseling, and clinical decision making/management.

Novel X‐linked syndrome of cardiac valvulopathy, keloid scarring, and reduced joint mobility due to filamin A substitution G1576R

Filamin A (FLNA) is known to be involved in intracellular actin binding, cell migration, scaffolding, and signaling. We report a novel X‐linked syndrome characterized by cardiac valvular disease, keloid scarring and reduced joint mobility in male second cousins due to a previously unreported mutation in FLNA. Whole exome sequencing was performed using standard methods and segregation analysis was performed in affected and non‐affected family members. A novel hemizygous c.4726G>A (p.G1576R) mutation in FLNA was detected. Segregation analysis performed on multiple maternal family members showed c.4726G>A (p.G1576R) segregated with disease in an X‐linked inheritance pattern. The findings in these cases are distinct from previously described FLNA related disorders by virtue of decreased joint mobility and spontaneous keloid scarring. They occur in association with a novel mutation and represent a novel genetic syndrome.

Biallelic Variants in OTUD6B Cause an Intellectual Disability Syndrome Associated with Seizures and Dysmorphic Features

Ubiquitination is a posttranslational modification that regulates many cellular processes including protein degradation, intracellular trafficking, cell signaling, and protein-protein interactions. Deubiquitinating enzymes (DUBs), which reverse the process of ubiquitination, are important regulators of the ubiquitin system. OTUD6B encodes a member of the ovarian tumor domain (OTU)-containing subfamily of deubiquitinating enzymes. Herein, we report biallelic pathogenic variants in OTUD6B in 12 individuals from 6 independent families with an intellectual disability syndrome associated with seizures and dysmorphic features. In subjects with predicted loss-of-function alleles, additional features include global developmental delay, microcephaly, absent speech, hypotonia, growth retardation with prenatal onset, feeding difficulties, structural brain abnormalities, congenital malformations including congenital heart disease, and musculoskeletal features. Homozygous Otud6b knockout mice were subviable, smaller in size, and had congenital heart defects, consistent with the severity of loss-of-function variants in humans. Analysis of peripheral blood mononuclear cells from an affected subject showed reduced incorporation of 19S subunits into 26S proteasomes, decreased chymotrypsin-like activity, and accumulation of ubiquitin-protein conjugates. Our findings suggest a role for OTUD6B in proteasome function, establish that defective OTUD6B function underlies a multisystemic human disorder, and provide additional evidence for the emerging relationship between the ubiquitin system and human disease.

De Novo Truncating Variants in SON Cause Intellectual Disability, Congenital Malformations, and Failure to Thrive

SON is a key component of the spliceosomal complex and a critical mediator of constitutive and alternative splicing. Additionally, SON has been shown to influence cell-cycle progression, genomic integrity, and maintenance of pluripotency in stem cell populations. The clear functional relevance of SON in coordinating essential cellular processes and its presence in diverse human tissues suggests that intact SON might be crucial for normal growth and development. However, the phenotypic effects of deleterious germline variants in SON have not been clearly defined. Herein, we describe seven unrelated individuals with de novo variants in SON and propose that deleterious variants in SON are associated with a severe multisystem disorder characterized by developmental delay, persistent feeding difficulties, and congenital malformations, including brain anomalies.

Misattributed parentage as an unanticipated finding during exome/genome sequencing: current clinical laboratory practices and an opportunity for standardization

PurposeClinical laboratories performing exome or genome sequencing (ES/GS) are familiar with the challenges associated with proper consenting for and reporting of medically actionable secondary findings based on recommendations from the American College of Medical Genetics and Genomics (ACMG). Misattributed parentage is another type of unanticipated finding a laboratory may encounter during family-based ES/GS; however, there are currently no professional recommendations related to the proper consenting for and reporting of misattributed parentage encountered during ES/GS.MethodsWe surveyed 10 clinical laboratories offering family-based ES/GS regarding their consent language, discovery, and reporting of misattributed parentage.ResultsMany laboratories have already developed their own practices/policies for these issues, which do not necessarily agree with those from other labs.ConclusionThere are several other possibilities besides true misattributed parentage that could result in similar laboratory findings, and laboratories often feel they lack sufficient information to make formal conclusions on a report regarding the true genetic relatedness of the submitted samples. However, understanding the genetic relatedness (or lack thereof) of the samples submitted for family-based ES/GS has medical relevance. Therefore, professional recommendations for the appropriate handling of suspected misattributed parentage encountered during ES/GS are needed to help standardize current clinical laboratory practices.

Two de novo novel mutations in one SHANK3 allele in a patient with autism and moderate intellectual disability

SHANK3 encodes for a scaffolding protein that links neurotransmitter receptors to the cytoskeleton and is enriched in postsynaptic densities of excitatory synapses. Deletions or mutations in one copy of the SHANK3 gene cause Phelan‐McDermid syndrome, also called 22q13.3 deletion syndrome, a neurodevelopmental disorder with common features including global developmental delay, absent to severely impaired language, autistic behavior, and minor dysmorphic features. By whole exome sequencing, we identified two de novo novel variants including one frameshift pathogenic variant and one missense variant of unknown significance in a 14‐year‐old boy with delayed motor milestones, delayed language acquisition, autism, intellectual disability, ataxia, progressively worsening spasticity of the lower extremities, dysmorphic features, short stature, microcephaly, failure to thrive, chronic constipation, intrauterine growth restriction, and bilateral inguinal hernias. Both changes are within the CpG island in exon 21, separated by a 375 bp sequence. Next generation sequencing of PCR products revealed that the two variants are most frequently associated with each other. Sanger sequencing of the cloned PCR products further confirmed that both changes were on a single allele. The clinical presentation in this individual is consistent with other patients with a truncating mutation in exon 21, suggesting that the missense change contributes none or minimally to the phenotypes. This is the first report of two de novo mutations in one SHANK3 allele.