This result suggests that COL4A3 and COL4A4 digenic mutations in cis mimicking an autosomal dominant inheritance should be considered as a novel inheritance pattern of benign familial hematuria, although the disease-causing mechanism remains unknown.
COL4A5 mutations are associated with the major X-linked form of the disease, and COL4A3 and COL4A4 mutations are associated with autosomal recessive and dominant forms (thought to be involved in 15% and 1%-5% of the families, respectively) and benign familial hematuria.
Gene mutations in COL4A5 located on Xq22 are believed to cause X-linked Alport syndrome, whereas mutations in COL4A3 and COL4A4 located on chromosome 2 are associated with autosomal inherited Alport syndrome or benign familial hematuria.
Altogether, these data make difficult the differential diagnosis with the benign familial haematuria due to heterozygous mutations of COL4A4 and COL4A3, especially in young patients, and with the X-linked form of Alport syndrome in families where only females are affected.
Three heterozygous mutations in the COL4A3 gene (two missense and one frameshift) and four heterozygous mutations in COL4A4 (two splice site, one in-frame deletion, and one missense) were identified in patients with BFH.
This study confirms that persistent familial hematuria is not always linked to COL4A3/COL4A4 (or COL4A5) and suggests the possibility of a further genetic locus for benign familial hematuria.
It became evident in recent years that mutations in the COL4A3 or the COL4A4 gene can give rise not only to autosomal recessive ATS syndrome, in which males and females are severely affected, but also to an autosomal dominant form, where the clinical progression towards impaired renal function can be very slow and also to benign familial hematuria (BFH) in which renal function is preserved.
The present study describes molecular changes of the COL4A4 gene that cause both diseases: autosomal recessive AS and BFH in a consanguine family with a 400-year-old history of haematuria.
Mutations of COL4A3 and COL4A4 have been reported both in autosomal-recessive and autosomal-dominant ATS, as well as in benign familial hematuria (BFH).
On electron microscopy, thickness of the glomerular basement membrane (BGM) was found to distinguish benign familial hematuria (BFH - 10 cases) from non familial idiopathic recurrent hematuria (IRH - 9 cases).