Gain and loss of TASK3 channel function and its regulation by novel variation cause KCNK9 imprinting syndrome.

BACKGROUND: Genomics enables individualized diagnosis and treatment, but large challenges remain to functionally interpret rare variants. To date, only one causative variant has been described for KCNK9 imprinting syndrome (KIS). The genotypic and phenotypic spectrum of KIS has yet to be described and the precise mechanism of disease fully understood. METHODS: This study discovers mechanisms underlying KCNK9 imprinting syndrome (KIS) by describing 15 novel KCNK9 alterations from 47 KIS-affected individuals. We use clinical genetics and computer-assisted facial phenotyping to describe the phenotypic spectrum of KIS. We then interrogate the functional effects of the variants in the encoded TASK3 channel using sequence-based analysis, 3D molecular mechanic and dynamic protein modeling, and in vitro electrophysiological and functional methodologies. RESULTS: We describe the broader genetic and phenotypic variability for KIS in a cohort of individuals identifying an additional mutational hotspot at p.Arg131 and demonstrating the common features of this neurodevelopmental disorder to include motor and speech delay, intellectual disability, early feeding difficulties, muscular hypotonia, behavioral abnormalities, and dysmorphic features. The computational protein modeling and in vitro electrophysiological studies discover variability of the impact of KCNK9 variants on TASK3 channel function identifying variants causing gain and others causing loss of conductance. The most consistent functional impact of KCNK9 genetic variants, however, was altered channel regulation. CONCLUSIONS: This study extends our understanding of KIS mechanisms demonstrating its complex etiology including gain and loss of channel function and consistent loss of channel regulation. These data are rapidly applicable to diagnostic strategies, as KIS is not identifiable from clinical features alone and thus should be molecularly diagnosed. Furthermore, our data suggests unique therapeutic strategies may be needed to address the specific functional consequences of KCNK9 variation on channel function and regulation.

PURA-Related Developmental and Epileptic Encephalopathy: Phenotypic and Genotypic Spectrum.

BACKGROUND AND OBJECTIVES: Purine-rich element-binding protein A (PURA) gene encodes Pur-α, a conserved protein essential for normal postnatal brain development. Recently, a PURA syndrome characterized by intellectual disability, hypotonia, epilepsy, and dysmorphic features was suggested. The aim of this study was to define and expand the phenotypic spectrum of PURA syndrome by collecting data, including EEG, from a large cohort of affected patients. METHODS: Data on unpublished and published cases were collected through the PURA Syndrome Foundation and the literature. Data on clinical, genetic, neuroimaging, and neurophysiologic features were obtained. RESULTS: A cohort of 142 patients was included. Characteristics of the PURA syndrome included neonatal hypotonia, feeding difficulties, and respiratory distress. Sixty percent of the patients developed epilepsy with myoclonic, generalized tonic-clonic, focal seizures, and/or epileptic spasms. EEG showed generalized, multifocal, or focal epileptic abnormalities. Lennox-Gastaut was the most common epilepsy syndrome. Drug refractoriness was common: 33.3% achieved seizure freedom. We found 97 pathogenic variants in PURA without any clear genotype-phenotype associations. DISCUSSION: The PURA syndrome presents with a developmental and epileptic encephalopathy with characteristics recognizable from neonatal age, which should prompt genetic screening. Sixty percent have drug-resistant epilepsy with focal or generalized seizures. We collected more than 90 pathogenic variants without observing overt genotype-phenotype associations.

A novel mutation of BEST1 gene in Best disease.

PURPOSE: To describe a new genetic variation of BEST1 gene in Best vitelliform macular dystrophy. METHODS: A patient with bilateral multiple retinal yellowish lesions at the posterior pole underwent fluorescein angiography, fundus autofluorescence, optical coherence tomography, electrooculogram and blood sample for genetic testing. RESULTS: A diagnosis of a Best vitelliform macular dystrophy was made. Heterozygous mutation c.76G > A (p.Gly26Ser) in exon 2 of the BEST1 gene was found. CONCLUSION: These findings contribute to expand the mutation spectrum of BEST1 gene.

Clinical Genetics Can Solve the Pitfalls of Genome-Wide Investigations: Lesson from Mismapping a Loss-of-Function Variant in KANSL1.

Massive parallel sequencing of 70 genes in a girl with a suspicion of chromatinopathy detected the (NM_015443.4:)c.985_986delTT variant in exon 2 of KANSL1, which led to a diagnostic consideration of Koolen De Vries syndrome. The same variant was present in the healthy mother, consistent with either incomplete penetrance or variant mismapping. A network of second opinion was implemented among clinical geneticists first, and a diagnosis of Koolen De Vries syndrome was considered unlikely. By MLPA, a duplication spanning exons 1-3 of KANSL1 was detected in both the mother and the daughter. On cDNA sequencing, biallelic wild type mRNA was observed. We concluded that the variant affects the noncoding duplicated gene region in our family, and we finally classified it as benign. Parallel wide genomic sequencing is increasingly the first genetic investigation in individuals with intellectual disability. The c.985_986delTT variant in KANSL1 was described both in individuals with typical KdVS and in a limited number of healthy subjects. This report highlights the role of clinical genetics to correctly classify variants and to define proper clinical and diagnostic correlations.

Homozygous Recessive Versican Missense Variation Is Associated With Early Teeth Loss in a Pakistani Family.

Only a few genes involved in teeth development and morphology are known to be responsible for tooth abnormalities in Mendelian-inherited diseases. We studied an inbred family of Pakistani origin in which two first-cousin born brothers are affected by early tooth loss with peculiar teeth abnormalities characterized by the absence of cementum formation. Whole exome sequencing revealed a H2665L homozygous sequence variant in the VCAN gene. Dominant splicing mutations in VCAN are known to cause Wagner syndrome or vitreoretinopathy. We explored teeth morphology in these two patients, while versican expression was assessed by western blot analysis. Early signs of vitreoretinopathy were found in the elder brother while the parents were completely negative. Our findings suggest that the homozygous recessive H2665L missense sequence variant impairs the normal morphology of the teeth roots via loss of cementum synthesis, and is also associated with early onset, recessive, Wagner syndrome, thus expanding both the phenotype mutation scenario and the inheritance mode of VCAN mutations.