Further evidence of RNU4ATAC variants causing Joubert syndrome with skeletal involvement

RNU4ATAC is a non-coding gene involved in the minor spliceosome, and is mutated in a spectrum of syndromic skeletal disorders with recessive inheritance. Recently, biallelic RNU4ATAC pathogenic variants were detected in five patients presenting a complex syndromic phenotype and a brain malformation resembling the ‘molar tooth sign’ (MTS). This is the hallmark of Joubert syndrome (JS), a neurodevelopmental ciliopathy with multiorgan involvement. We reanalysed exome sequencing (ES) from 53 patients with JS, who lacked coding variants in known JS-associated genes. Four RNU4ATAC variants (n.16G>A, n.51G>A, n.13C>T and n.30G>A) were identified in compound heterozygosity in three probands, accounting for 5.6% of negative cases. All patients displayed the MTS and clinical features overlapping those of JS and RNU4ATAC -related skeletal disorders. These findings expand the phenotypic spectrum of RNU4ATAC -related disorders to include a complex neurological-skeletal ciliopathy phenotype, and highlight the relevance of ES reanalysis to uncover non-coding variants often undetected by conventional diagnostics.