COL4A1 and muscle cramp: Type IV collagen mutations, most of them causing glycine changes in Gly-X-Y motifs, were also found in human COL4A1 and with lesser frequency in COL4A2 in connection with various diseases such as porencephaly, hemorrhagic stroke, small vessel disease and the Hereditary Angiopathy with Nephropathy, Aneurysms, and Muscle Cramps (HANAC) Syndrome [41,43,90].