The sister of the proband was found to be a compound heterozygote for the same two ATP7B variants carried by her brother, while lacking the c.160G > A variant and being heterozygous ATG/GTG (Met + Val) at codon 129 of PRNP. However, despite exhibiting a classical biochemical phenotype for Wilson’s disease with a low serum copper level of 2.1 μmol/L, a low ceruloplasmin of 0.12 g/L, and a high 24 h urine copper level of 1.1 μmol (normal values as above), she was asymptomatic, with a normal MRI and neurological examination. The gene discussed is PRNP; the disease is Wilson disease.