COL4A4 and Alzheimer disease: Females heterozygous for mutations in COL4A5 that cause X-linked AS have a variable phenotype, with ∼15% eventually developing ESRD, at a median age of 49 years—a risk broadly similar to that seen in individuals with AD TBMN who are heterozygous for pathogenic autosomal COL4A3 and COL4A4 mutations [11, 12].