Search

Reference population databases like the Genome Aggregation Database (gnomAD) have improved our ability to interpret the human genome. Variant frequencies and frequency-derived tools (such as depletion scores) have become fundamental to variant interpretation and the assessment of variant-gene-disease relationships. Clonal hematopoiesis (CH) obstructs variant interpretation as somatic variants that provide proliferative advantage will affect variant frequencies, depletion scores, and downstream filtering. Further, default filtering of variants or genes associated with CH risks filtering bona fide germline variants as variants associated with CH can also cause Mendelian conditions. Here, we provide our insights on interpreting population variant data in genes affected by clonal hematopoiesis, as well as recommendations for careful review of 36 established CH genes associated with neurodevelopmental conditions., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Purpose: ZMYND8 encodes a multidomain protein that serves as a central interactive hub for coordinating critical roles in transcription regulation, chromatin remodeling, regulation of super-enhancers, DNA damage response and tumor suppression. We delineate a novel neurocognitive disorder caused by variants in the ZMYND8 gene., Methods: An international collaboration, exome sequencing, molecular modeling, yeast two-hybrid assays, analysis of available transcriptomic data and a knockdown Drosophila model were used to characterize the ZMYND8 variants., Results: ZMYND8 variants were identified in 11 unrelated individuals; 10 occurred de novo and one suspected de novo; 2 were truncating, 9 were missense, of which one was recurrent. The disorder is characterized by intellectual disability with variable cardiovascular, ophthalmologic and minor skeletal anomalies. Missense variants in the PWWP domain of ZMYND8 abolish the interaction with Drebrin and missense variants in the MYND domain disrupt the interaction with GATAD2A. ZMYND8 is broadly expressed across cell types in all brain regions and shows highest expression in the early stages of brain development. Neuronal knockdown of the DrosophilaZMYND8 ortholog results in decreased habituation learning, consistent with a role in cognitive function., Conclusion: We present genomic and functional evidence for disruption of ZMYND8 as a novel etiology of syndromic intellectual disability., Competing Interests: Conflict of Interest S.V.M., T.B.P., and M.J.G.S. are employees of GeneDx, Inc. All other authors declare no conflicts of interest., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Non-canonical intronic variants are a poorly characterized yet highly prevalent class of alterations associated with Mendelian disorders. Here, we report the first RNA expression and splicing analysis from a family whose members carry a non-canonical splice variant in an intron of RPL11 (c.396 +3A>G). This mutation is causative for Diamond Blackfan Anemia (DBA) in this family despite incomplete penetrance and variable expressivity. Our analyses revealed a complex pattern of disruptions with many novel junctions of RPL11. These include an RPL11 transcript that is translated with a late stop codon in the 3' untranslated region (3'UTR) of the main isoform. We observed that RPL11 transcript abundance is comparable among carriers regardless of symptom severity. Interestingly, both the small and large ribosomal subunit transcripts were significantly overexpressed in individuals with a history of anemia in addition to congenital abnormalities. Finally, we discovered that coordinated expression between mitochondrial components and RPL11 was lost in all carriers, which may lead to variable expressivity. Overall, this study highlights the importance of RNA splicing and expression analyses in families for molecular characterization of Mendelian diseases., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

Gene sequencing panels are a powerful diagnostic tool for many clinical presentations associated with genetic disorders. Advances in DNA sequencing technology have made gene panels more economical, flexible, and efficient. Because the genes included on gene panels vary widely between laboratories in gene content (e.g., number, reason for inclusion, evidence level for gene-disease association) and technical completeness (e.g., depth of coverage), standards that address technical and clinical aspects of gene panels are needed. This document serves as a technical standard for laboratories designing, offering, and reporting gene panel testing. Although these principles can apply to multiple indications for genetic testing, the primary focus is on diagnostic gene panels (as opposed to carrier screening or predictive testing) with emphasis on technical considerations for the specific genes being tested. This technical standard specifically addresses the impact of gene panel content on clinical sensitivity, specificity, and validity-in the context of gene evidence for contribution to and strength of evidence for gene-disease association-as well as technical considerations such as sequencing limitations, presence of pseudogenes/gene families, mosaicism, transcript choice, detection of copy-number variants, reporting, and disclosure of assay limitations.

The NONO gene encodes a nuclear protein involved in RNA metabolism. Hemizygous loss-of-function NONO variants have been associated with syndromic intellectual disability and with left ventricular noncompaction (LVNC). A two-year-old boy presented to the University of Utah's Penelope Undiagnosed Disease Program with developmental delay, nonfamilial features, relative macrocephaly, and dilated cardiomyopathy with LVNC and Ebstein anomaly. Brain MRI showed a thick corpus callosum, mild Chiari I malformation, and a flattened pituitary. Exome sequencing identified a novel intronic deletion (c.154+5_154+6delGT) in the NONO gene. Splicing studies demonstrated intron 4 read-through and the use of an alternative donor causing the frameshift p.Asn52Serfs*6. Family segregation analysis showed that the variant occurred de novo in the boy's unaffected mother. MRI and endocrine findings suggest that hypopituitarism may contribute to growth failure, abnormal thyroid hormone levels, cryptorchidism, or delayed puberty in patients with NONO-associated disease. Also, including this case LVNC has been observed in five out of eight patients, and this report also confirms an association between loss of NONO and Ebstein anomaly. In some cases, unrelated individuals share the same pathogenic NONO variants but do not all have clinically significant LVNC, suggesting that additional modifiers may contribute to cardiac phenotypes., (© 2019 Wiley Periodicals, Inc.)

SPONASTRIME dysplasia is an autosomal-recessive spondyloepimetaphyseal dysplasia characterized by spine (spondylar) abnormalities, midface hypoplasia with a depressed nasal bridge, metaphyseal striations, and disproportionate short stature. Scoliosis, coxa vara, childhood cataracts, short dental roots, and hypogammaglobulinemia have also been reported in this disorder. Although an autosomal-recessive inheritance pattern has been hypothesized, pathogenic variants in a specific gene have not been discovered in individuals with SPONASTRIME dysplasia. Here, we identified bi-allelic variants in TONSL, which encodes the Tonsoku-like DNA repair protein, in nine subjects (from eight families) with SPONASTRIME dysplasia, and four subjects (from three families) with short stature of varied severity and spondylometaphyseal dysplasia with or without immunologic and hematologic abnormalities, but no definitive metaphyseal striations at diagnosis. The finding of early embryonic lethality in a Tonsl -/- murine model and the discovery of reduced length, spinal abnormalities, reduced numbers of neutrophils, and early lethality in a tonsl -/- zebrafish model both support the hypomorphic nature of the identified TONSL variants. Moreover, functional studies revealed increased amounts of spontaneous replication fork stalling and chromosomal aberrations, as well as fewer camptothecin (CPT)-induced RAD51 foci in subject-derived cell lines. Importantly, these cellular defects were rescued upon re-expression of wild-type (WT) TONSL; this rescue is consistent with the hypothesis that hypomorphic TONSL variants are pathogenic. Overall, our studies in humans, mice, zebrafish, and subject-derived cell lines confirm that pathogenic variants in TONSL impair DNA replication and homologous recombination-dependent repair processes, and they lead to a spectrum of skeletal dysplasia phenotypes with numerous extra-skeletal manifestations., (Copyright © 2019 American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

Loss-of-function and hypomorphic ECHS1 variants are associated with mitochondrial short-chain enoyl-CoA hydratase deficiency, an inborn error of valine metabolism. We report an 8-year-old boy with developmental delay, ataxia, hemiplegia, and hearing loss with abnormalities in the basal ganglia. Biochemical studies were essentially normal except for a persistent mildly elevated CSF alanine. This patient demonstrates an intermediate phenotype between a Leigh-like, early-onset presentation and paroxysmal exercise-induced dyskinesia. Two novel ECHS1 variants (c.79T>G; p.Phe27Val and c.789_790del; p.Phe263fs) were identified via exome sequencing in the proband, and pathogenicity was confirmed by enzyme assay performed on patient fibroblasts. Neither of the ECHS1 variants detected in the child were present in the mother. However, due to nearby polymorphisms, it was possible to determine that p.Phe263fs occurred de novo on the maternal chromosome and that p.Phe27Val likely derived from the paternal chromosome. Nearby polymorphisms can help set phase of variants when only a single parent is available for testing or when an identified variant occurs de novo.

Connexin 26 (Cx26), encoded by the GJB2 gene, is a key protein involved in the formation of gap junctions in epithelial organs including the inner ear and palmoplantar epidermis. Pathogenic variants in GJB2 are responsible for approximately 50% of inherited sensorineural deafness. The majority of these variants are associated with autosomal recessive inheritance; however, rare reports of dominantly co-segregating variants have been published. Since we began offering GJB2 testing in 2003, only about 2% of detected GJB2 variants from our laboratory have been classified as dominant. Here we report three novel dominant GJB2 variants (p.Thr55Ala, p.Gln57_Pro58delinsHisSer, and p.Trp44Gly); two associated with syndromic sensorineural hearing loss and one with nonsyndromic hearing loss. In the kindred with the p.Thr55Ala variant, the proband and his father present with only leukonychia as a cutaneous finding of their syndromic hearing loss. This phenotype has been previously documented in conjunction with palmoplantar hyperkeratosis, but isolated leukonychia is a novel finding likely associated with the unique threonine to alanine change at codon 55 (other variants at this codon have been reported in cases of nonsyndromic hearing loss). This report contributes to the short list of GJB2 variants associated with autosomal dominant hearing loss, highlights the variability of skin and nail findings associated with such cases, and illustrates the occurrence of both syndromic and nonsyndromic presentations with changes in the same gene., (© 2018 Wiley Periodicals, Inc.)

De novo, germline variants in DNMT3A cause Tatton-Brown-Rahman syndrome (TBRS). This condition is characterized by overgrowth, distinctive facial appearance, and intellectual disability. Somatic DNMT3A variants frequently occur in hematologic malignances, particularly acute myeloid leukemia. The Arg882 residue is the most common site of somatic DNMT3A variants, and has also been altered in patients with TBRS. Here we present three additional patients with this disorder attributed to DNMT3A germline variants that disrupt the Arg882 codon, suggesting that this codon may be a germline mutation hotspot in this disorder. Furthermore, based on the investigation of previously reported variants in patients with TBRS, we found overlap in the spectrum of DNMT3A variants observed in this disorder and somatic variants in hematological malignancies., (© 2017 Wiley Periodicals, Inc.)

Diamond-Blackfan anemia (DBA) is a group of clinically and genetically heterogeneous bone marrow failure disorders with or without congenital anomalies. Variable expressivity and incomplete penetrance have been observed within affected families. Diamond-Blackfan anemia-7 (DBA7), caused by heterozygous mutations in ribosomal protein L11 (RPL11), accounts for approximately 5% of DBA. DBA7 is usually characterized by early-onset bone marrow failure often accompanied by congenital malformations, especially thumb defects. Here, we present the case of a 2-year-old boy with chronic mild normocytic anemia, short stature, bilateral underdevelopment of the thumbs, atrial septal defect, and hypospadias. Hematological testing revealed slightly decreased hematocrit and hemoglobin, normal HbF, and elevated eADA. Family history included maternal relatives with thumb defects, but the mother's thumbs were normal. Clinical exome sequencing detected a maternally-inherited RPL11 variant, c.396+3A>G, that is predicted to affect splicing. A family correlation study of the identified variant demonstrates segregation with thumb anomalies in the mother's family. RNA studies suggest that the variant produces an alternative transcript that is likely susceptible to nonsense-mediated decay. This report summarizes the prevalence of non-anemia findings in DBA7 and describes a non-classical familial presentation of DBA7 more associated with thumb anomalies than with anemia., (© 2017 Wiley Periodicals, Inc.)

The clinical interpretation of genetic variants has come to rely heavily on reference population databases such as the Exome Aggregation Consortium (ExAC) database. Pathogenic variants in genes associated with severe, pediatric-onset, highly penetrant, autosomal dominant conditions are assumed to be absent or rare in these databases. Exome sequencing of a 6-year-old female patient with seizures, developmental delay, dysmorphic features, and failure to thrive identified an ASXL1 variant previously reported as causative of Bohring-Opitz syndrome (BOS). Surprisingly, the variant was observed seven times in the ExAC database, presumably in individuals without BOS. Although the BOS phenotype fit, the presence of the variant in reference population databases introduced ambiguity in result interpretation. Review of the literature revealed that acquired somatic mosaicism of ASXL1 variants (including pathogenic variants) during hematopoietic clonal expansion can occur with aging in healthy individuals. We examined all ASXL1 truncating variants in the ExAC database and determined most are likely somatic. Failure to consider somatic mosaicism may lead to the inaccurate assumption that conditions like BOS have reduced penetrance, or the misclassification of potentially pathogenic variants., (© 2017 Wiley Periodicals, Inc.)