Spectrum of KV 2.1 Dysfunction in KCNB1-Associated Neurodevelopmental Disorders.

OBJECTIVE: Pathogenic variants in KCNB1, encoding the voltage-gated potassium channel KV 2.1, are associated with developmental and epileptic encephalopathy (DEE). Previous functional studies on a limited number of KCNB1 variants indicated a range of molecular mechanisms by which variants affect channel function, including loss of voltage sensitivity, loss of ion selectivity, and reduced cell-surface expression. METHODS: We evaluated a series of 17 KCNB1 variants associated with DEE or other neurodevelopmental disorders (NDDs) to rapidly ascertain channel dysfunction using high-throughput functional assays. Specifically, we investigated the biophysical properties and cell-surface expression of variant KV 2.1 channels expressed in heterologous cells using high-throughput automated electrophysiology and immunocytochemistry-flow cytometry. RESULTS: Pathogenic variants exhibited diverse functional defects, including altered current density and shifts in the voltage dependence of activation and/or inactivation, as homotetramers or when coexpressed with wild-type KV 2.1. Quantification of protein expression also identified variants with reduced total KV 2.1 expression or deficient cell-surface expression. INTERPRETATION: Our study establishes a platform for rapid screening of KV 2.1 functional defects caused by KCNB1 variants associated with DEE and other NDDs. This will aid in establishing KCNB1 variant pathogenicity and the mechanism of dysfunction, which will enable targeted strategies for therapeutic intervention based on molecular phenotype. ANN NEUROL 2019;86:899-912.

Genotype-phenotype analysis of 523 patients by genetics evaluation and clinical exome sequencing.

BACKGROUND: As clinical exome sequencing (CES) becomes more common, understanding which patients are most likely to benefit and in what manner is critical for the general pediatrics community to appreciate. METHODS: Five hundred and twenty-three patients referred to the Pediatric Genetics clinic at Michigan Medicine were systematically phenotyped by the presence or absence of abnormalities for 13 body/organ systems by a Clinical Genetics team. All patients then underwent CES. RESULTS: Overall, 30% of patients who underwent CES had an identified pathogenic mutation. The most common phenotypes were developmental delay (83%), neuromuscular system abnormalities (81%), and multiple congenital anomalies (42%). In all, 67% of patients had a variant of uncertain significance (VUS) or gene of uncertain significance (GUS); 23% had no variants reported. There was a significant difference in the average number of body systems affected among these groups (pathogenic 5.89, VUS 6.0, GUS 6.12, and no variant 4.6; P < 0.00001). Representative cases highlight four ways in which CES is changing clinical pediatric practice. CONCLUSIONS: Patients with identified variants are enriched for multiple organ system involvement. Furthermore, our phenotyping provides broad insights into which patients are most likely to benefit from genetics referral and CES and how those results can help guide clinical practice more generally.

Phenotype of CM-AVM2 caused by variants in EPHB4: how much overlap with hereditary hemorrhagic telangiectasia (HHT)?

PURPOSE: EPHB4 variants were recently reported to cause capillary malformation-arteriovenous malformation 2 (CM-AVM2). CM-AVM2 mimics RASA1-related CM-AVM1 and hereditary hemorrhagic telangiectasia (HHT), as clinical features include capillary malformations (CMs), telangiectasia, and arteriovenous malformations (AVMs). Epistaxis, another clinical feature that overlaps with HHT, was reported in several cases. Based on the clinical overlap of CM-AVM2 and HHT, we hypothesized that patients considered clinically suspicious for HHT with no variant detected in an HHT gene (ENG, ACVRL1, or SMAD4) may have an EPHB4 variant. METHODS: Exome sequencing or a next-generation sequencing panel including EPHB4 was performed on individuals with previously negative molecular genetic testing for the HHT genes and/or RASA1. RESULTS: An EPHB4 variant was identified in ten unrelated cases. Seven cases had a pathogenic EPHB4 variant, including one with mosaicism. Three cases had an EPHB4 variant of uncertain significance. The majority had epistaxis (6/10 cases) and telangiectasia (8/10 cases), as well as CMs. Two of ten cases had a central nervous system AVM. CONCLUSIONS: Our results emphasize the importance of considering CM-AVM2 as part of the clinical differential for HHT and other vascular malformation syndromes. Yet, these cases highlight significant differences in the cutaneous presentations of CM-AVM2 versus HHT.

Expanding the phenotypic spectrum of MBOAT7-related intellectual disability.

MBOAT7 gene pathogenic variants are a newly discovered and rare cause for intellectual disability, autism spectrum disorder (ASD), seizures, truncal hypotonia, appendicular hypertonia, and below average head sizes (ranging from -1 to -3 standard deviations). There have been only 16 individuals previously reported who have MBOAT7-related intellectual disability, all of whom were younger than 10 years old and from consanguineous relationships. Thus, there is a lack of phenotypic information for adolescent and adult individuals with this disorder. Medical genetics and psychiatric evaluations in a 14-year-old female patient with a history of global developmental delay, intellectual disability, overgrowth with macrocephaly, metrorrhagia, seizures, basal ganglia hyperintensities, nystagmus, strabismus with amblyopia, ASD, anxiety, attention deficit hyperactivity disorder (ADHD), aggressive outbursts, and hyperphagia included a karyotype, methylation polymerase chain reaction for Prader-Willi/Angelman syndrome, chromosome microarray, and whole exome sequencing (WES), ADOS2, and ADI-R. WES identified a homozygous, likely pathogenic variant in the MBOAT7 gene (c.855-2A>G). This is the oldest known patient with MBOAT7-related intellectual disability, whose unique features compared with previously described individuals include overgrowth with macrocephaly, metrorrhagia, ophthalmological abnormalities, basal ganglia hyperintensities, unspecified anxiety disorder, and ADHD; combined type; and hyperphagia with the absence of appendicular hypertonia and cortical atrophy. More individuals need to be identified in order to delineate the full clinical spectrum of this disorder.

Interstitial microdeletion of the 1p34.3p34.2 region.

BACKGROUND: Interstitial microdeletions of chromosome 1p34.3p34.2 are rare, but are continuing to be identified by the use of chromosome microarray. There have been fewer than 10 individuals identified who have deletions of the 1p34.3p34.2 region; all of these previously described individuals have deletions of the AGO1, AGO3, GRIK3, SLC2A1, or RIMS3 genes. Haploinsufficiency of these genes has been associated with neurodevelopmental delays. METHODS: Chromosome microarray, quantitative PCR, and fluorescence in situ hybridization were performed with DNA extracted from peripheral blood. RESULTS: Chromosome microarray identified a 2.3 Mb 1p34.3p34.2 one copy deletion in our patient with global developmental delay, mild intellectual disability, delayed bone age, bilateral vesicoureteral reflux, vocal cord paralysis, right aberrant subclavian artery, kyphoscoliosis, bilateral metatarsus adductus, and valgus knee deformity. This deletion was confirmed by quantitative PCR and does not include the AGO1, AGO3, GRIK3, SLC2A1, or RIMS3 genes. Subsequent FISH testing of the parents was negative. CONCLUSION: Haploinsufficiency of the 1p34.3p34.2 region, including the SNIP1 gene and excluding the five genes listed above, is responsible for the neurocognitive delays and other symptoms as identified in our patient.

Pulmonary arterial hypertension: Specialists' knowledge, practices, and attitudes of genetic counseling and genetic testing in the USA.

Pulmonary arterial hypertension (PAH) is characterized by obstruction of pre-capillary pulmonary arteries, which leads to sustained elevation of pulmonary arterial pressure. Identifying those at risk through early interventions, such as genetic testing, may mitigate disease course. Current practice guidelines recommend genetic counseling and offering genetic testing to individuals with heritable PAH, idiopathic PAH, and their family members. However, it is unclear if PAH specialists follow these recommendations. Thus, our research objective was to determine PAH specialists' knowledge, utilization, and perceptions about genetic counseling and genetic testing. A survey was designed and distributed to PAH specialists who primarily work in the USA to assess their knowledge, practices, and attitudes about the genetics of PAH. Participants' responses were analyzed using parametric and non-parametric statistics and groups were compared using the Wilcoxon rank sum test. PAH specialists had low perceived and actual knowledge of the genetics of PAH, with 13.2% perceiving themselves as knowledgeable and 27% actually being knowledgeable. Although these specialists had positive or ambivalent attitudes about genetic testing and genetic counseling, they had poor utilization of these genetic services, with almost 80% of participants never or rarely ordering genetic testing or referring their patients with PAH for genetic counseling. Physicians were more knowledgeable, but had lower perceptions of the value of genetic testing and genetic counseling compared to non-physicians ( P < 0.05). The results suggest that increased education and awareness is needed about the genetics of PAH as well as the benefits of genetic testing and genetic counseling for individuals who treat patients with PAH.