COL4A3 and Andersen-Tawil syndrome: Thus far, according to the ClinVar database (89, 110), 405 of 997 variants in COL4A3 and 526 of 1,105 variants in COL4A4 have been reported in confirmed autosomal ATS cases, while 1,075 of 1,801 COL4A5 variants have been reported in ATS1 cases.