ABCC6 and Pseudoxanthoma elasticum: Four additional variants were excluded because they were associated with a mild condition, including stationary night blindness (GPR179, MIM #614565), mild cystinuria (SLC7A9, MIM #220100), postaxial polydactyly (IQCE, MIM# 617642) and pseudoxanthoma elasticum (ABCC6, MIM #264800).