Diagnostic implications of pitfalls in causal variant identification based on 4577 molecularly characterized families

Despite large sequencing and data sharing efforts, previously characterized pathogenic variants only account for a fraction of Mendelian disease patients, which highlights the need for accurate identification and interpretation of novel variants. In a large Mendelian cohort of 4577 molecularly characterized families, numerous scenarios in which variant identification and interpretation can be challenging are encountered. We describe categories of challenges that cover the phenotype (e.g. novel allelic disorders), pedigree structure (e.g. imprinting disorders masquerading as autosomal recessive phenotypes), positional mapping (e.g. double recombination events abrogating candidate autozygous intervals), gene (e.g. novel gene-disease assertion) and variant (e.g. complex compound inheritance). Overall, we estimate a probability of 34.3% for encountering at least one of these challenges. Importantly, our data show that by only addressing non-sequencing-based challenges, around 71% increase in the diagnostic yield can be expected. Indeed, by applying these lessons to a cohort of 314 cases with negative clinical exome or genome reports, we could identify the likely causal variant in 54.5%. Our work highlights the need to have a thorough approach to undiagnosed diseases by considering a wide range of challenges rather than a narrow focus on sequencing technologies. It is hoped that by sharing this experience, the yield of undiagnosed disease programs globally can be improved

Testis development in the absence of SRY: chromosomal rearrangements at SOX9 and SOX3.

Duplications in the ~2 Mb desert region upstream of SOX9 at 17q24.3 may result in familial 46,XX disorders of sex development (DSD) without any effects on the XY background. A balanced translocation with its breakpoint falling within the same region has also been described in one XX DSD subject. We analyzed, by conventional and molecular cytogenetics, 19 novel SRY-negative unrelated 46,XX subjects both familial and sporadic, with isolated DSD. One of them had a de novo reciprocal t(11;17) translocation. Two cases carried partially overlapping 17q24.3 duplications ~500 kb upstream of SOX9, both inherited from their normal fathers. Breakpoints cloning showed that both duplications were in tandem, whereas the 17q in the reciprocal translocation was broken at ~800 kb upstream of SOX9, which is not only close to a previously described 46,XX DSD translocation, but also to translocations without any effects on the gonadal development. A further XX male, ascertained because of intellectual disability, carried a de novo cryptic duplication at Xq27.1, involving SOX3. CNVs involving SOX3 or its flanking regions have been reported in four XX DSD subjects. Collectively in our cohort of 19 novel cases of SRY-negative 46,XX DSD, the duplications upstream of SOX9 account for ~10.5% of the cases, and are responsible for the disease phenotype, even when inherited from a normal father. Translocations interrupting this region may also affect the gonadal development, possibly depending on the chromatin context of the recipient chromosome. SOX3 duplications may substitute SRY in some XX subject

Oncogenic Nras has bimodal effects on stem cells that sustainably increase competitiveness

“Pre-leukemic” mutations are thought to promote clonal expansion of haematopoietic stem cells (HSCs) by increasing self-renewal and competitiveness(1); however, mutations that increase HSC proliferation tend to reduce competitiveness and self-renewal potential, raising the question of how a mutant HSC can sustainably outcompete wild-type HSCs. Activating mutations in NRAS are prevalent in human myeloproliferative neoplasms and leukemia(2). Here we show that a single allele of oncogenic Nras(G12D) increases HSC proliferation but also increases reconstituting and self-renewal potential upon serial transplantation in irradiated mice, all prior to leukemia initiation. Nras(G12D) also confers long-term self-renewal potential upon multipotent progenitors. To explore the mechanism by which Nras(G12D) promotes HSC proliferation and self-renewal we assessed cell cycle kinetics using H2B-GFP label retention and BrdU incorporation. Nras(G12D) had a bimodal effect on HSCs, increasing the rate at which some HSCs divide and reducing the rate at which others divide. This mirrored bimodal effects on reconstituting potential as rarely dividing Nras(G12D) HSCs outcompeted wild-type HSCs while frequently dividing Nras(G12D) HSCs did not. Nras(G12D) had these effects by promoting STAT5 signaling, inducing different transcriptional responses in different subsets of HSCs. One signal can therefore increase HSC proliferation, competitiveness, and self-renewal through bimodal effects on HSC gene expression, cycling, and reconstituting potential

Mutation in NRAS in familial Noonan syndrome - case report and review of the literature

Genetics of disease, diagnosis and treatmen

Germline homozygous missense DEPDC5 variants cause severe refractory early-onset epilepsy, macrocephaly and bilateral polymicrogyria.

DEPDC5 (DEP Domain-Containing Protein 5) encodes an inhibitory component of the mammalian target of rapamycin (mTOR) pathway and is commonly implicated in sporadic and familial focal epilepsies, both non-lesional and in association with focal cortical dysplasia. Germline pathogenic variants are typically heterozygous and inactivating. We describe a novel phenotype caused by germline biallelic missense variants in DEPDC5. Cases were identified clinically. Available records, including magnetic resonance imaging and electroencephalography, were reviewed. Genetic testing was performed by whole exome and whole-genome sequencing and cascade screening. In addition, immunohistochemistry was performed on skin biopsy. The phenotype was identified in nine children, eight of which are described in detail herein. Six of the children were of Irish Traveller, two of Tunisian and one of Lebanese origin. The Irish Traveller children shared the same DEPDC5 germline homozygous missense variant (p.Thr337Arg), whereas the Lebanese and Tunisian children shared a different germline homozygous variant (p.Arg806Cys). Consistent phenotypic features included extensive bilateral polymicrogyria, congenital macrocephaly and early-onset refractory epilepsy, in keeping with other mTOR-opathies. Eye and cardiac involvement and severe neutropenia were also observed in one or more patients. Five of the children died in infancy or childhood; the other four are currently aged between 5 months and 6 years. Skin biopsy immunohistochemistry was supportive of hyperactivation of the mTOR pathway. The clinical, histopathological and genetic evidence supports a causal role for the homozygous DEPDC5 variants, expanding our understanding of the biology of this gene

Germline homozygous missense DEPDC5 variants cause severe refractory early-onset epilepsy, macrocephaly and bilateral polymicrogyria

PURPOSE: DEPDC5 (DEP Domain-Containing Protein 5) encodes an inhibitory component of the mTOR pathway and is commonly implicated in sporadic and familial focal epilepsies, both non-lesional and in association with focal cortical dysplasia. Germline pathogenic variants are typically heterozygous and inactivating. We describe a novel phenotype caused by germline biallelic missense variants in DEPDC5. METHODS: Cases were identified clinically. Available records, including MRI and EEG, were reviewed. Genetic testing was performed by whole exome and whole genome sequencing and cascade screening. In addition, immunohistochemistry was performed on skin biopsy. RESULTS: The phenotype was identified in nine children, eight of which are described in detail herein. Six of the children were of Irish Traveller, two of Tunisian and one of Lebanese origin. The Irish Traveller children shared the same DEPDC5 germline homozygous missense variant (p.Thr337Arg), whereas the Lebanese and Tunisian children shared a different germline homozygous variant (p.Arg806Cys). Consistent phenotypic features included extensive bilateral polymicrogyria, congenital macrocephaly and early-onset refractory epilepsy, in keeping with other mTOR-opathies. Eye and cardiac involvement, and severe neutropenia, were also observed in one or more patients. Five of the children died in infancy or childhood, the other four are currently aged between five months and six years. Skin biopsy immunohistochemistry was supportive of hyperactivation of the mTOR pathway. DISCUSSION: The clinical, histopathological and genetic evidence supports a causal role for the homozygous DEPDC5 variants, expanding our understanding of the biology of this gene.Published version, accepted version (12 month embargo), submitted versionThis article is freely available online. Click on the 'Additional Link' above to access the full-text via the publisher's site