Novel <i>HYLS1</i> variants associated with Joubert syndrome suggest potential genotype-phenotype correlates

Joubert syndrome (JS) is an inherited neurodevelopmental ciliopathy with wide clinical and genetic heterogeneity, whose paradigmatic sign is a peculiar cerebellar and brainstem malformation known as the 'molar tooth sign'. Recessive pathogenic variants in the <i>HYLS1</i> gene are associated with hydrolethalus syndrome (HLS), a severe disorder characterised by multiple developmental defects leading to intrauterine or perinatal death. However, <i>HYLS1</i> biallelic variants were also reported in three individuals with JS.Here, we report a fourth patient with a purely neurological JS carrying two compound heterozygous missense variants in the <i>HYLS1</i> gene. Notably, while all patients with lethal HLS had both variants falling within the highly conserved HYLS-1 Box, the four patients with milder JS phenotype featured at least one variant external to this evolutionary conserved domain, suggesting a possible correlation between the mutation site and the severity of the phenotype.