Epidemiology

Epidemiology

TBMN has been reported in all races, although most of the cases thus far have been reported in developed countries. Hematuria has been diagnosed at all ages (8,11,43), and several studies have indicated that the disease is somewhat more common in female than in male individuals, among both children and adults (8,17,18,27,42–47), but other studies have not revealed such findings (26,48–50). Exact prevalence of the disease is difficult to assess, as the diagnosis is made mostly on the basis of persistent hematuria combined with minimal proteinuria, whereas the number of electron microscopic analyses of renal biopsies showing thinned basement membrane have become less common (51). Thus, most of the cases remain undiagnosed. However, the prevalence may be estimated from known frequencies of persistent hematuria in the population and from the number of TBMN cases in archival series of renal biopsies, together with the knowledge of prevalence of autosomal Alport syndrome (51). Several studies have addressed the prevalence of hematuria and persistent hematuria in children and adults (52–56). Persistent hematuria is commonly defined as hematuria that is observed on at least two occasions, and in TBMN, a useful additional criterion could be that these two incidents occurred at least 2 yr apart (51). Persistence of hematuria is important from the point of view of TBMN diagnosis, as it distinguishes from other, more acute renal disorders, such as hematuria associated with streptococcal infections (51). The prevalence of hematuria in children has been estimated to be 1 to 2% (52,53), but the prevalence in adults is not well known (3). According to Wang and Savige (51), persistent hematuria occurs consistently in as much as 6% of both children and adults. On the basis of both direct and indirect approaches, the overall prevalence of TBMN in the population has been estimated to be 1% (3). However, on the basis of observations of frequencies of persistent hematuria, thin basement membrane in renal biopsies, and autosomal recessive Alport syndrome, another estimate indicates a higher prevalence of >1 but <10% (51). When making estimations about the prevalence of TBMN by analyzing incidence of hematuria, one should keep in mind that not all patients who have TBMN have hematuria (or it is intermittent), that some patients with persistent hematuria have other signs of renal impairment (excluding the diagnosis of TBMN), and last that hematuria is not always of glomerular origin. It can be concluded, however, that TBMN is the most common inherited renal disorder.

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Karl Tryggvason and 

Jaakko Patrakka