Occurrence and characterization of medulloblastoma in a patient with Curry-Jones syndrome.

Medulloblastoma in a Patient with Curry-Jones Syndrome with a mosaic variant, c.1234C > T (p.Leu412Phe), in SMO.

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.

Dual Molecular Effects of Dominant RORA Mutations Cause Two Variants of Syndromic Intellectual Disability with Either Autism or Cerebellar Ataxia.

RORα, the RAR-related orphan nuclear receptor alpha, is essential for cerebellar development. The spontaneous mutant mouse staggerer, with an ataxic gait caused by neurodegeneration of cerebellar Purkinje cells, was discovered two decades ago to result from homozygous intragenic Rora deletions. However, RORA mutations were hitherto undocumented in humans. Through a multi-centric collaboration, we identified three copy-number variant deletions (two de novo and one dominantly inherited in three generations), one de novo disrupting duplication, and nine de novo point mutations (three truncating, one canonical splice site, and five missense mutations) involving RORA in 16 individuals from 13 families with variable neurodevelopmental delay and intellectual disability (ID)-associated autistic features, cerebellar ataxia, and epilepsy. Consistent with the human and mouse data, disruption of the D. rerio ortholog, roraa, causes significant reduction in the size of the developing cerebellum. Systematic in vivo complementation studies showed that, whereas wild-type human RORA mRNA could complement the cerebellar pathology, missense variants had two distinct pathogenic mechanisms of either haploinsufficiency or a dominant toxic effect according to their localization in the ligand-binding or DNA-binding domains, respectively. This dichotomous direction of effect is likely relevant to the phenotype in humans: individuals with loss-of-function variants leading to haploinsufficiency show ID with autistic features, while individuals with de novo dominant toxic variants present with ID, ataxia, and cerebellar atrophy. Our combined genetic and functional data highlight the complex mutational landscape at the human RORA locus and suggest that dual mutational effects likely determine phenotypic outcome.

A novel epileptic encephalopathy mutation in KCNB1 disrupts Kv2.1 ion selectivity, expression, and localization.

The epileptic encephalopathies are a group of highly heterogeneous genetic disorders. The majority of disease-causing mutations alter genes encoding voltage-gated ion channels, neurotransmitter receptors, or synaptic proteins. We have identified a novel de novo pathogenic K+ channel variant in an idiopathic epileptic encephalopathy family. Here, we report the effects of this mutation on channel function and heterologous expression in cell lines. We present a case report of infantile epileptic encephalopathy in a young girl, and trio-exome sequencing to determine the genetic etiology of her disorder. The patient was heterozygous for a de novo missense variant in the coding region of the KCNB1 gene, c.1133T>C. The variant encodes a V378A mutation in the α subunit of the Kv2.1 voltage-gated K+ channel, which is expressed at high levels in central neurons and is an important regulator of neuronal excitability. We found that expression of the V378A variant results in voltage-activated currents that are sensitive to the selective Kv2 channel blocker guangxitoxin-1E. These voltage-activated Kv2.1 V378A currents were nonselective among monovalent cations. Striking cell background-dependent differences in expression and subcellular localization of the V378A mutation were observed in heterologous cells. Further, coexpression of V378A subunits and wild-type Kv2.1 subunits reciprocally affects their respective trafficking characteristics. A recent study reported epileptic encephalopathy-linked missense variants that render Kv2.1 a tonically activated, nonselective cation channel that is not voltage activated. Our findings strengthen the correlation between mutations that result in loss of Kv2.1 ion selectivity and development of epileptic encephalopathy. However, the strong voltage sensitivity of currents from the V378A mutant indicates that the loss of voltage-sensitive gating seen in all other reported disease mutants is not required for an epileptic encephalopathy phenotype. In addition to electrophysiological differences, we suggest that defects in expression and subcellular localization of Kv2.1 V378A channels could contribute to the pathophysiology of this KCNB1 variant.

Expanding the phenotype of feingold syndrome-2.

Feingold syndrome-2 has been recently shown to be caused by germline heterozygous deletions of MIR17HG with 10 reported patients to date. Manifestations common to both Feingold syndrome-1 and Feingold syndrome-2 include microcephaly, short stature, and brachymesophalangy; but those with Feingold syndrome-2 lack gastrointestinal atresias. Here we describe a 14-year-old male patient who presented to our Cardiovascular Genetics Clinic with a history of a bicuspid aortic valve with aortic stenosis, short stature, hearing loss, and mild learning disabilities. Upon examination he was noted to have dysmorphic features and brachydactyly of his fingers and toes. His head circumference was 54.5 cm (25th-50th centile) and his height was 161.3 cm (31st centile) after growth hormone therapy. A skeletal survey noted numerous abnormalities prompting suspicion for Feingold syndrome. A comparative genomic hybridization microarray was completed and a ∼3.6 Mb interstitial heterozygous deletion at 13q31.3 including MIR17HG was found consistent with Feingold syndrome-2. Clinically, this patient has the characteristic digital anomalies and short stature often seen in Feingold syndrome-2 with less common features of a congenital heart defect and hearing loss. Although non-skeletal features have been occasionally reported in Feingold syndrome-1, only one other patient with a 13q31 microdeletion including MIR17HG has had non-skeletal manifestations. Additionally, our patient does not have microcephaly and, to our knowledge, is the first reported pediatric patient with Feingold syndrome-2 without this feature. This report illustrates significant phenotypic variability within the clinical presentation of Feingold syndrome-2 and highlights considerable overlap with Feingold syndrome-1.

A patient with polymerase E1 deficiency (POLE1): clinical features and overlap with DNA breakage/instability syndromes.

BACKGROUND: Chromosome instability syndromes are a group of inherited conditions associated with chromosomal instability and breakage, often leading to immunodeficiency, growth retardation and increased risk of malignancy. CASE PRESENTATION: We performed exome sequencing on a girl with a suspected chromosome instability syndrome that manifested as growth retardation, microcephaly, developmental delay, dysmorphic features, poikiloderma, immune deficiency with pancytopenia, and myelodysplasia. She was homozygous for a previously reported splice variant, c.4444 + 3A > G in the POLE1 gene, which encodes the catalytic subunit of DNA polymerase E. CONCLUSION: This is the second family with POLE1-deficency, with the affected individual demonstrating a more severe phenotype than previously described.

Variable approaches to genetic counseling for microarray regions of homozygosity associated with parental relatedness.

SNP microarrays are capable of detecting regions of homozygosity (ROH) which can suggest parental relatedness. This study was designed to describe pre- and post-test counseling practices of genetics professionals regarding ROH, explore perceived comfort and ethical concerns in the follow-up of such results, demonstrate awareness of laws surrounding duty to report consanguinity and incest, and allow respondents to share their personal experiences with results suggesting a parental relationship. A 35 question survey was administered to 240 genetic counselors and geneticists who had ordered or counseled for SNP microarray. The results are presented using descriptive statistics. There was variation in both pre- and post-test counseling practices of genetics professionals. Twenty-five percent of respondents reported pre-test counseling that ROH can indicate parental relatedness. The most commonly reported ethical concern was disclosure of findings suggesting parental relatedness to parents of the patient; only 48.4% reported disclosing parental relatedness when indicated. Fifty-seven percent felt comfortable receiving results suggesting parental consanguinity while 17% felt comfortable receiving results suggesting parental incest. Twenty percent of respondents were extremely/moderately familiar with the laws about duty to report incest. Personal experiences in post-test counseling included both parental acknowledgement and denial of relatedness. This study highlights the differences in genetics professionals' pre- and post-test counseling practices, comfort, and experiences surrounding parental relatedness suggested by SNP microarray results. It identifies a need for professional organizations to offer guidance to genetics professionals about how to respond to and counsel for molecular results suggesting parental consanguinity or incest.

Regions of homozygosity identified by SNP microarray analysis aid in the diagnosis of autosomal recessive disease and incidentally detect parental blood relationships.

PURPOSE: The purpose of this study was to document the ability of single-nucleotide polymorphism microarray to identify copy-neutral regions of homozygosity, demonstrate clinical utility of regions of homozygosity, and discuss ethical/legal implications when regions of homozygosity are associated with a parental blood relationship. METHODS: Study data were compiled from consecutive samples sent to our clinical laboratory over a 3-year period. A cytogenetics database identified patients with at least two regions of homozygosity >10 Mb on two separate chromosomes. A chart review was conducted on patients who met the criteria. RESULTS: Of 3,217 single-nucleotide polymorphism microarrays, 59 (1.8%) patients met inclusion criteria. The percentage of homozygosity ranged from 0.9 to 30.1%, indicating parental relationships from distant to first-degree relatives. First-degree kinship was suspected in the parents of at least 11 patients with regions of homozygosity covering >21.3% of their autosome. In four patients from two families, homozygosity mapping discovered a candidate gene that was sequenced to identify a clinically significant mutation. CONCLUSION: This study demonstrates clinical utility in the identification of regions of homozygosity, as these regions may aid in diagnosis of the patient. This study establishes the need for careful reporting, thorough pretest counseling, and careful electronic documentation, as microarray has the capability of detecting previously unknown/unreported relationships.

Variability in laboratory reporting practices for regions of homozygosity indicating parental relatedness as identified by SNP microarray testing.

PURPOSE: Single-nucleotide polymorphism (SNP) microarrays are capable of detecting regions of homozygosity (ROH) that can suggest parental consanguinity or incest. This study was designed to describe the variable reporting practices of clinical laboratories in the United States regarding ROH found on SNP microarray tests, to discuss the follow-up practices of laboratory personnel when findings of ROH indicate consanguinity or incest, and to highlight the legal and ethical dilemmas faced by workers who have discovered these incidental findings. METHODS: A 20-question survey was administered to microarray experts at 18 laboratories offering clinical SNP microarray tests. The results are presented using descriptive statistics. RESULTS: There was variability in laboratory SNP microarray reporting practices with respect to information and interpretation of ROH findings. All the laboratories agreed that they have a duty to inform the ordering physician about results suggesting consanguinity or incest, but the follow-through practices varied among laboratories. CONCLUSIONS: This study discovered variability in reporting practices and follow-up procedures for microarray results that suggest parental consanguinity or incest. Our findings highlight the need for laboratory guidelines to standardize reporting practices for SNP microarray and other tests that are capable of detecting ROH.