Alport syndrome and other collagen disorders

Type IV collagen is a ubiquitous component of basement membranes along with laminin, entactin/nidogen, and heparan sulfate proteoglycans. Six type IV collagen genes (COL4A1-COL4A6) encode six unique alpha chains of type IV collagen [α1(IV)-α6(IV)]. Mutations in several of the type IV collagen genes can cause a number of progressive and nonprogressive glomerular disorders. Mutations in COL4A3, COL4A4, and COL4A5 may cause Alport syndrome (AS), an inherited kidney disease that classically leads to ESKD, sensorineural hearing loss, and eye abnormalities in affected individuals. Mutations in COL4A6 along with COL4A5 are associated with AS accompanied by leiomyomatosis. Heterozygous mutations in COL4A3 and COL4A4 are associated with thin basement membrane nephropathy (TBMN), a generally nonprogressive kidney disorder presenting with isolated microscopic hematuria. Finally, mutations in COL4A1 cause hereditary angiopathy with nephropathy, aneurysms, and muscle cramps (HANAC) syndrome. This chapter will review the genetics, clinical manifestations, pathology, diagnosis, and treatment of each of these type IV collagen disorders.