One of the three patients carried a homozygous duplication (c.764 dupA) in exon 6 of the CTSD gene, thereby creating a premature stop codon and loss of CathD expression; another patient was his older sibling, who died of the same disease phenotype and thus, most probably, carried the same mutation, while the third, unrelated patient with congenital NCL had no detectable CathD protein present in her tissues although she remains genetically unidentified [30]. This evidence concerns the gene CTSD and neuronal ceroid lipofuscinosis.