The Role of Double Heterozygotes of SLC3A1 and SLC7A9 in the Prevalence of Cystine Stones.

PURPOSE: Cystine stones, an autosomal recessive disorder caused by cystinuria, result from pathogenic variants of SLC3A1 and SLC7A9. Previous publications revealed clinical prevalence is higher than genetically predicted prevalence. Heterozygous carriers in either gene are not stone formers. However, double heterozygotes (DH), individuals with two heterozygous pathogenic variants in both genes, were never evaluated and may explain the gap between clinical and genetic prevalence. METHODS: Due to the rarity of the condition, direct clinical observation is impractical. We perform this population study as a surrogate by identifying the observed DH, deriving the theoretical/expected DH, and testing the null hypothesis (NH) that the observed DH frequency is equal or greater than expected. This NH biologically correlates to DH are asymptomatic and without cystine stone. RESULTS: Using the 1000 Genome Database, we identified 0 DH. We derived the theoretical/expected DH with Hardy-Weinberg Equilibrium and Mendel's law of independent assortment, as 4.94x10-s. Population proportion test revealed Z= -0.353, and p= 0.362, the NH cannot be rejected. CONCLUSION: Statistical testing does not support that DH are symptomatic, i.e. DH of SLC3A1 and SLC7A9 may not present with cystine stone, and other factors responsible for the gap that current genetics knowledge cannot explain.

NCKAP1 Disruptive Variants Lead to a Neurodevelopmental Disorder with Core Features of Autism.

NCKAP1/NAP1 regulates neuronal cytoskeletal dynamics and is essential for neuronal differentiation in the developing brain. Deleterious variants in NCKAP1 have been identified in individuals with autism spectrum disorder (ASD) and intellectual disability; however, its clinical significance remains unclear. To determine its significance, we assemble genotype and phenotype data for 21 affected individuals from 20 unrelated families with predicted deleterious variants in NCKAP1. This includes 16 individuals with de novo (n = 8), transmitted (n = 6), or inheritance unknown (n = 2) truncating variants, two individuals with structural variants, and three with potentially disruptive de novo missense variants. We report a de novo and ultra-rare deleterious variant burden of NCKAP1 in individuals with neurodevelopmental disorders which needs further replication. ASD or autistic features, language and motor delay, and variable expression of intellectual or learning disability are common clinical features. Among inherited cases, there is evidence of deleterious variants segregating with neuropsychiatric disorders. Based on available human brain transcriptomic data, we show that NCKAP1 is broadly and highly expressed in both prenatal and postnatal periods and demostrate enriched expression in excitatory neurons and radial glias but depleted expression in inhibitory neurons. Mouse in utero electroporation experiments reveal that Nckap1 loss of function promotes neuronal migration during early cortical development. Combined, these data support a role for disruptive NCKAP1 variants in neurodevelopmental delay/autism, possibly by interfering with neuronal migration early in cortical development.

Erratum: Variants in PHF8 cause a spectrum of X-linked neurodevelopmental disorders and facial dysmorphology.

[This corrects the article DOI: 10.1016/j.xhgg.2022.100102.].