COL4A3 and Andersen-Tawil syndrome: Genotype/phenotype correlations in our study are consistent with a semidominant pattern of inheritance of the COL4A3 and COL4A4 variants and suggest that the renal functional prognosis of patients with COL4A3‐ or COL4A4‐positive ATS recapitulates the phenotypic pattern of the X‐linked ATS forms, with the outcome of the COL4A3 and COL4A4 heterozygotes being very similar to that of XLAS carrier females, whereas the compound COL4A3 and COL4A4 heterozygosity reproduces the severe prognosis of XLAS‐affected males (Figure 1, Panel A).