Genomic DNA was extracted from whole blood from the affected children and their parents. Exome sequencing at GeneDx was performed on exon targets captured using the Agilent SureSelect Human All Exon V4 (50 Mb) or the Clinical Research Exome kit (Agilent Technologies) according to the manufacturer's instructions. Libraries were sequenced using the Illumina HiSeq 2000 or 2500 sequencing system with 100-bp paired-end reads (Illumina). Whole-exome sequence data for all sequenced family members was analyzed using GeneDx's XomeAnalyzer (a variant annotation, filtering, and viewing interface for exome sequencing data) as described previously (Tanaka et al. 2017 (link)). The identified sequence variant of interest was confirmed in the proband, affected siblings, and both parents by conventional di-deoxy DNA sequence analysis using an ABI3730 (Life Technologies).