The Many Faces of Thin Basement Membrane Nephropathy; A Population Based Study

Thin basement membrane nephropathy (TBMN) or benign familial hematuria, is one of the commonest kidney disorders, characterized by recurrent benign hematuria, which is often associated with a family history (Gregory, 2005). It is generally considered to be a nonprogressive, life long disorder with a rather benign course (Tryggvason & Patrakka, 2006), although data from some studies show that a proportion of patients manifest more severe symptoms, than originally described and eventually develop endstage renal disease (ESRD) (Dische, Weston, & Parsons, 1985; Frasca et al., 2005; Pierides et al., 2009; Tiebosch et al., 1989). TBMN was first described in 1926 (Baer, 1926) and at presentation is usually characterized by microscopic painless hematuria, by little or negligible proteinuria and normal renal function. TBMN is an autosomal dominant disorder and more than 50% of the cases have a family history of hematuria. In about 40% of families with a confirmed diagnosis of TBMN the condition co-segregates with heterozygous COL4A3/COL4A4 mutations (Lemmink et al., 1996). Mutations in the type IV collagen gene family which also includes the COL4A5 gene, also cause Alport syndrome (Hostikka et al., 1990). It is believed that these disorders are the result of defective, synthesis and/or assembly, of the critical glycoprotein components, that form the glomerular basement membranes (GBMs), among which type IV collagen, is the major constituent. Clinically TBMN must be differentially diagnosed, between IgA nephropathy and Alport syndrome which are the other two main causes of hematuria, particularly in children. The need for differential diagnosis, often necessitates the examination of a kidney biopsy at the electron microscopical level, which also enables measurement of the thickness of the GBMs. Indeed Rogers et al (Rogers, Kurtzman, Bunn, & White, 1973) were the first to associate recurrent benign hematuria with the presence of thin GBMs. Currently the most widely