The present study reports the clinical and genetic features of 76 patients from 34 unrelated ATS families with mutations in COL4A3, COL4A4, or COL4A5 variants identified using NGS technology, with a special focus on the genotype/phenotype correlations in patients with heterozygous COL4A3 and COL4A4 variants. The gene discussed is COL4A3; the disease is Andersen-Tawil syndrome.