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Item Identification of PKD1L1 Gene Variants in Children with the Biliary Atresia Splenic Malformation Syndrome(Wiley, 2019) Berauer, John-Paul; Mezina, Anya I.; Okou, David T.; Sabo, Aniko; Muzny, Donna M.; Gibbs, Richard A.; Hegde, Madhuri R.; Chopra, Pankaj; Cutler, David J.; Perlmutter, David H.; Bull, Laura N.; Thompson, Richard J.; Loomes, Kathleen M.; Spinner, Nancy B.; Rajagopalan, Ramakrishnan; Guthery, Stephen L.; Moore, Barry; Yandell, Mark; Harpavat, Sanjiv; Magee, John C.; Kamath, Binita M.; Molleston, Jean P.; Bezerra, Jorge A.; Murray, Karen F.; Alonso, Estella M.; Rosenthal, Philip; Squires, Robert H.; Wang, Kasper S.; Finegold, Milton J.; Russo, Pierre; Sherker, Averell H.; Sokol, Ronald J.; Karpen, Saul J.; Pediatrics, School of MedicineBiliary atresia (BA) is the most common cause of end‐stage liver disease in children and the primary indication for pediatric liver transplantation, yet underlying etiologies remain unknown. Approximately 10% of infants affected by BA exhibit various laterality defects (heterotaxy) including splenic abnormalities and complex cardiac malformations — a distinctive subgroup commonly referred to as the biliary atresia splenic malformation (BASM) syndrome. We hypothesized that genetic factors linking laterality features with the etiopathogenesis of BA in BASM patients could be identified through whole exome sequencing (WES) of an affected cohort. DNA specimens from 67 BASM subjects, including 58 patient‐parent trios, from the NIDDK‐supported Childhood Liver Disease Research Network (ChiLDReN) underwent WES. Candidate gene variants derived from a pre‐specified set of 2,016 genes associated with ciliary dysgenesis and/or dysfunction or cholestasis were prioritized according to pathogenicity, population frequency, and mode of inheritance. Five BASM subjects harbored rare and potentially deleterious bi‐allelic variants in polycystin 1‐like 1, PKD1L1, a gene associated with ciliary calcium signaling and embryonic laterality determination in fish, mice and humans. Heterozygous PKD1L1 variants were found in 3 additional subjects. Immunohistochemical analysis of liver from the one BASM subject available revealed decreased PKD1L1 expression in bile duct epithelium when compared to normal livers and livers affected by other non‐cholestatic diseases. Conclusion WES identified bi‐allelic and heterozygous PKD1L1 variants of interest in 8 BASM subjects from the ChiLDReN dataset. The dual roles for PKD1L1 in laterality determination and ciliary function suggest that PKD1L1 is a new, biologically plausible, cholangiocyte‐expressed candidate gene for the BASM syndrome.Item Whole exome sequencing and co-expression analysis identify an SCN1A variant that modifies pathogenicity in a family with Genetic Epilepsy and Febrile Seizures Plus (GEFS+)(Wiley, 2022) Hammer, Michael F.; Pan, Yanling; Cumbay, Medhane; Pendziwiat, Manuela; Afawi, Zaid; Goldberg-Stern, Hadassah; Johnstone, Laurel; Helbig, Ingo; Cummins, Theodore R.; Biology, School of ScienceObjective Family members carrying the same SCN1A variant often exhibit differences in the clinical severity of epilepsy. This variable expressivity suggests that other factors aside from the primary sodium channel variant influence the clinical manifestation. However, identifying such factors has proven challenging in humans. Methods We perform whole exome sequencing in a large family in which an SCN1A variant (p.K1372E) is segregating that is associated with a broad spectrum of phenotypes ranging from lack of epilepsy, to febrile seizures and absence seizures, to Dravet Syndrome. We assessed the hypothesis that the severity of SCN1A-related phenotype was affected by alternate alleles at a modifier locus (or loci). Results One of our top candidates identified by WES was a second variant in the SCN1A gene (p.L375S) that was exclusively shared by unaffected carriers of K1372E allele. To test the hypothesized that L375S nullifies the loss-of-function effect of K1372E, we transiently expressed Nav1.1 carrying the two variants in HEK293T cells and compared their biophysical properties with the wild-type (WT) variant, and then co-expressed WT with K1372E or L375S with K1372E in equal quantity and tested the functional consequence. The data demonstrated that co-expression of the L375S and K1372E alleles reversed the loss-of-function property brought by the K1372E variant, while WT-K1372E co-expression remained partial loss-of-function. Significance These results support the hypothesis that L375S counteracts the loss-of-function effect of K1372E such that individuals carrying both alleles in trans do not present epilepsy-related symptoms. We demonstrate that monogenic epilepsies with wide expressivity can be modified by additional variants in the disease gene, providing a novel framework for gene-phenotype relationship in genetic epilepsies.