X-Linked Disorders:

Alport syndrome is caused by pathogenic changes in the genes that code for type IV collagen, the primary component of basement membranes. Basement membranes are specialized nets of tissue that form a strong backbone of support for the lining of many connective tissue membranes (13). Alport syndrome weakens the basement membranes of blood vessels in the kidney, eyes, and ears, causing progressive renal failure, vision abnormalities, and hearing loss (12). There are three genes associated with Alport syndrome, but only COL4A5 is on the X chromosome (12). While the presentation of symptoms is similar between autosomal recessive inheritance and X-linked recessive inheritance,

• 85% of cases are inherited in an X-linked recessive pattern (14).

• 85% of cases are acquired via X-linked recessive inheritance of genetic variants on COL4A5 (14).

• 15% of cases are not X-linked disorders and are acquired via autosomal recessive inheritance of genetic variants on either COL4A3 or COL4A4 (14).

Written by Abigail Sayers; Images by Abigail Sayers unless otherwise noted

Reviewed and Edited by Rachel Baer, MSc, and Andy McCarty, MS, LGC, CGC

Learn More About Genetics:

• Sample Types

• Prenatal and Fetal Testing

• Aneuploidies

• Cytogenetics

Learn More About the X Chromosome:

• The X Chromosome

• X and Y Chromosomal Aneuploidies

• DMD and BMD

• Hemophilia A

• Red-Green Color Blindness

• Fabry Disease

• Fragile X Syndrome

• X-Linked Charcot-Marie-Tooth (CMTX)