The ACMG standards and guidelines classify the c.1272T>A (p.Cys424Ter) variant as pathogenic, and the detailed evidence is as follows: PVS1, a nonsense variant in the MOCOS gene where loss of function (LOF) is the mechanism underlying Xanthinuria type II; PM2_Supporting, the c.1272T>A variant is not included in the gnomAD database; and PP1_Supporting, segregation in two affected individuals in this family. Here, MOCOS is linked to xanthinuria type II.