Identification of a novel variant of FOXP3 resulting in severe immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome highlights potential pitfalls of molecular testing.

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare genetic disorder that typically presents in the first year of life with severe diarrhea, autoimmune endocrine disorder, and inflammatory dermatitis, most commonly an eczematous dermatitis. IPEX syndrome is caused by variants in the FOXP3 gene leading to dysregulation of T-regulatory (Treg) cells and an aberrant immune response. Here, we present a case of severe IPEX syndrome diagnosed following whole genome sequencing (WGS) in a 2-week-old boy with bloody mucoid diarrhea, failure to thrive, and a diffuse eczematous dermatitis. As multiple variants of interest were identified with WGS, this case highlights the importance of relating the clinical symptoms to the genetic results.

Rare deleterious mutations of HNRNP genes result in shared neurodevelopmental disorders.

BACKGROUND: With the increasing number of genomic sequencing studies, hundreds of genes have been implicated in neurodevelopmental disorders (NDDs). The rate of gene discovery far outpaces our understanding of genotype-phenotype correlations, with clinical characterization remaining a bottleneck for understanding NDDs. Most disease-associated Mendelian genes are members of gene families, and we hypothesize that those with related molecular function share clinical presentations. METHODS: We tested our hypothesis by considering gene families that have multiple members with an enrichment of de novo variants among NDDs, as determined by previous meta-analyses. One of these gene families is the heterogeneous nuclear ribonucleoproteins (hnRNPs), which has 33 members, five of which have been recently identified as NDD genes (HNRNPK, HNRNPU, HNRNPH1, HNRNPH2, and HNRNPR) and two of which have significant enrichment in our previous meta-analysis of probands with NDDs (HNRNPU and SYNCRIP). Utilizing protein homology, mutation analyses, gene expression analyses, and phenotypic characterization, we provide evidence for variation in 12 HNRNP genes as candidates for NDDs. Seven are potentially novel while the remaining genes in the family likely do not significantly contribute to NDD risk. RESULTS: We report 119 new NDD cases (64 de novo variants) through sequencing and international collaborations and combined with published clinical case reports. We consider 235 cases with gene-disruptive single-nucleotide variants or indels and 15 cases with small copy number variants. Three hnRNP-encoding genes reach nominal or exome-wide significance for de novo variant enrichment, while nine are candidates for pathogenic mutations. Comparison of HNRNP gene expression shows a pattern consistent with a role in cerebral cortical development with enriched expression among radial glial progenitors. Clinical assessment of probands (n = 188-221) expands the phenotypes associated with HNRNP rare variants, and phenotypes associated with variation in the HNRNP genes distinguishes them as a subgroup of NDDs. CONCLUSIONS: Overall, our novel approach of exploiting gene families in NDDs identifies new HNRNP-related disorders, expands the phenotypes of known HNRNP-related disorders, strongly implicates disruption of the hnRNPs as a whole in NDDs, and supports that NDD subtypes likely have shared molecular pathogenesis. To date, this is the first study to identify novel genetic disorders based on the presence of disorders in related genes. We also perform the first phenotypic analyses focusing on related genes. Finally, we show that radial glial expression of these genes is likely critical during neurodevelopment. This is important for diagnostics, as well as developing strategies to best study these genes for the development of therapeutics.

Temple syndrome resulting from uniparental disomy is undiagnosed by a methylation assay due to low-level mosaicism for trisomy 14.

We describe a patient with Temple syndrome resulting from maternal uniparental disomy of chromosome 14 who also has low-level mosaicism for trisomy 14. UPD was initially suspected when SNP microarray analysis detected a large region of homozygosity on chromosome 14 and the patient's clinical features were consistent with the phenotype of upd(14)mat. However, SNP arrays cannot prove UPD, as homozygosity may also result from identity by descent. Methylation assays diagnose imprinting disorders such as Prader-Willi, Angelman and Temple syndromes; they detect methylation defects that occur in imprinted loci, which have parent-of-origin-specific expression and have the advantage of making a diagnosis without parental samples. However, in this patient methylation analysis using endpoint PCR detected biparental inheritance. Therefore, sequencing analysis was performed and diagnosed upd(14)mat. Re-examination of the microarray suggested that the explanation for the discrepancy between the array and methylation testing was low-level mosaicism for trisomy 14 and fluorescence in situ hybridization testing detected a trisomic cell line. Thus, this patient's Temple syndrome is a result of a maternal M1 error, which gave a trisomic zygote, followed by loss of the paternal chromosome 14 in an early mitotic division to give maternal UPD with low-level mosaicism for trisomy 14. The methylation assay detected the paternal allele in the trisomic line. The diagnostic failure of the methylation assay in this patient highlights a significant shortcoming of methylation endpoint analysis, especially for Temple syndrome, and underscores the need to use other methods in cases with mosaicism.

A novel TSC1 variant associated with tuberous sclerosis and sacrococcygeal teratoma.

Tuberous sclerosis complex (TSC) is an autosomal dominant disease associated with tumors and malformed tissues in the brain and other vital organs. We report a novel de novo frameshift variant of the TSC1 gene (c.434dup;p. Ser146Valfs*8) in a child with TSC who initially presented with a sacral teratoma. This previously unreported association between TSC and teratoma has broad implications for the pathophysiology of embryonic tumors and mechanisms underlying cellular differentiation.

A homozygous founder mutation in TRAPPC6B associates with a neurodevelopmental disorder characterised by microcephaly, epilepsy and autistic features.

BACKGROUND: Transport protein particle (TRAPP) is a multisubunit complex that regulates membrane trafficking through the Golgi apparatus. The clinical phenotype associated with mutations in various TRAPP subunits has allowed elucidation of their functions in specific tissues. The role of some subunits in human disease, however, has not been fully established, and their functions remain uncertain. OBJECTIVE: We aimed to expand the range of neurodevelopmental disorders associated with mutations in TRAPP subunits by exome sequencing of consanguineous families. METHODS: Linkage and homozygosity mapping and candidate gene analysis were used to identify homozygous mutations in families. Patient fibroblasts were used to study splicing defect and zebrafish to model the disease. RESULTS: We identified six individuals from three unrelated families with a founder homozygous splice mutation in TRAPPC6B, encoding a core subunit of the complex TRAPP I. Patients manifested a neurodevelopmental disorder characterised by microcephaly, epilepsy and autistic features, and showed splicing defect. Zebrafish trappc6b morphants replicated the human phenotype, displaying decreased head size and neuronal hyperexcitability, leading to a lower seizure threshold. CONCLUSION: This study provides clinical and functional evidence of the role of TRAPPC6B in brain development and function.

Homozygous mutation in NUP107 leads to microcephaly with steroid-resistant nephrotic condition similar to Galloway-Mowat syndrome.

BACKGROUND: Microcephaly with nephrotic syndrome is a rare co-occurrence, constituting the Galloway-Mowat syndrome (GAMOS), caused by mutations in WDR73 (OMIM: 616144). However, not all patients harbour demonstrable WDR73 deleterious variants, suggesting that there are other yet unidentified factors contributing to GAMOS aetiology. METHODS: Autozygosity mapping and candidate analysis was used to identify deleterious variants in consanguineous families. Analysis of patient fibroblasts was used to study splicing and alterations in cellular function. RESULTS: In two consanguineous families with five affected individuals from Turkey with a GAMOS-like presentation, we identified a shared homozygous variant leading to partial exon 4 skipping in nucleoporin, 107-KD (NUP107). The founder mutation was associated with concomitant reduction in NUP107 protein and in the obligate binding partner NUP133 protein, as well as density of nuclear pores in patient cells. CONCLUSION: Recently, NUP107 was suggested as a candidate in a family with nephrotic syndrome and developmental delay. Other NUP107-reported cases had isolated renal phenotypes. With the addition of these individuals, we implicate an allele-specific critical role for NUP107 in the regulation of brain growth and a GAMOS-like presentation.

Xq11.1-11.2 deletion involving ARHGEF9 in a girl with autism spectrum disorder.

We report an 8-year-old female with autism spectrum disorder (ASD), intellectual disability and speech delay who was found to carry a de novo 82 kb deletion of chromosome Xq11.1-11.2 involving the ARHGEF9 gene on chromosomal microarray. So far, 11 patients with point mutations, disruptions due to chromosomal rearrangements and deletions involving ARHGEF9 have been reported in the literature. ARHGEF9-related disorders comprise a wide phenotypic spectrum, including behavior disorders, autism spectrum disorder, intellectual disability, hyperekplexia and infantile epileptic encephalopathy. ARHGEF9 encodes for collybistin which plays an important role in post synaptic clustering of glycine and inhibitory gamma-aminobutyric acid receptors along with its scaffolding partner, gephyrin. The reduction of inhibitory receptor clusters in brain has been proposed as a plausible underlying pathophysiological mechanism. With this report, we provide further evidence for the role of ARHGEF9 in neurocognitive function, its implication in ASD, and review the clinical features of previously published individuals with ARHGEF9-related intellectual disability.

PYCR2 Mutations cause a lethal syndrome of microcephaly and failure to thrive.

OBJECTIVE: A study was undertaken to characterize the clinical features of the newly described hypomyelinating leukodystrophy type 10 with microcephaly. This is an autosomal recessive disorder mapped to chromosome 1q42.12 due to mutations in the PYCR2 gene, encoding an enzyme involved in proline synthesis in mitochondria. METHODS: From several international clinics, 11 consanguineous families were identified with PYCR2 mutations by whole exome or targeted sequencing, with detailed clinical and radiological phenotyping. Selective mutations from patients were tested for effect on protein function. RESULTS: The characteristic clinical presentation of patients with PYCR2 mutations included failure to thrive, microcephaly, craniofacial dysmorphism, progressive psychomotor disability, hyperkinetic movements, and axial hypotonia with variable appendicular spasticity. Patients did not survive beyond the first decade of life. Brain magnetic resonance imaging showed global brain atrophy and white matter T2 hyperintensities. Routine serum metabolic profiles were unremarkable. Both nonsense and missense mutations were identified, which impaired protein multimerization. INTERPRETATION: PYCR2-related syndrome represents a clinically recognizable condition in which PYCR2 mutations lead to protein dysfunction, not detectable on routine biochemical assessments. Mutations predict a poor outcome, probably as a result of impaired mitochondrial function. Ann Neurol 2016;80:59-70.

Chromosomal microarray in prenatal diagnosis: case studies and clinical challenges.

Chromosomal microarray analysis (CMA) is a diagnostic tool used in the evaluation of pediatric patients with congenital anomalies or developmental and intellectual disability. In both the pediatric and prenatal patient population, CMA has been shown to have a higher detection rate of chromosomal abnormalities than conventional karyotype alone. Currently, the diagnostic yield of prenatal CMA is highest when applied to the evaluation of a fetus with multiple ultrasound anomalies. Challenges arise when CMA yields isolated findings not associated with a phenotype on ultrasound or variants of uncertain significance, which warrants evaluation of the risks, benefits, limitations and optimal incorporation of CMA into prenatal care. The clinical cases presented here will be used to illustrate these issues.

Expanding the clinical spectrum of late-onset Pompe disease: dilated arteriopathy involving the thoracic aorta, a novel vascular phenotype uncovered.

PURPOSE: Cerebro-vascular arteriopathy has been reported in late-onset Pompe disease (LOPD). Evidence of increased aortic stiffness in some patients and smooth muscle involvement in LOPD raises the possibility of aortic involvement. Our aim was to determine if aortic arteriopathy may be a complication of LOPD. METHODS: One patient with LOPD was diagnosed with aortic dilatation at Duke Metabolic clinic, 4 others were diagnosed at University of Mainz, Germany, where chest X-ray and echocardiography are routinely done for patients. Other causes of aortic vascular disease were assessed. RESULTS: We report evidence of dilated arteriopathy involving primarily the ascending thoracic aorta in 5 females with late-onset Pompe disease. One patient had a bicuspid aortic valve and developed dissection. Another patient with juvenile onset disease had both thoracic and basilar artery aneurysms. CONCLUSIONS: Aneurysmal dilatation of the thoracic aorta is an underreported vascular complication of LOPD, probably due to the same pathological process that occurs in the brain. Chest X-ray together with echocardiography should be incorporated as initial screening tools for aortic aneurysms in patients with LOPD. When ectasia is suspected, or the ascending aorta is not visualized, contrast- mediated thoracic CT or MRA may be necessary. Large-scale studies are warranted to determine the prevalence and extent of aortic vascular involvement.