Novel <i>FUCA1</i> variants in two families, including the first report of a contiguous gene deletion syndrome involving <i>FUCA1</i> and <i>HMGCL</i>

Fucosidosis should be considered in patients with delayed motor and cognitive development followed by progressive neurological deterioration, even in the absence of common features such as organomegaly and angiokeratoma. The pathogenic variants identified in both families were novel and consistent with fucosidosis type 1. To our knowledge, this is the first reported case of fucosidosis accompanied by 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) lyase deficiency resulting from a contiguous gene deletion involving the HMGCL gene at the 1p36.11 locus.