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Alport syndrome is a genetically heterogeneous disorder with autosomal dominant, autosomal recessive and X-linked inheritance. The estimated prevalence is about 1 in 50,000 live births. All forms are caused by mutations in the genes encoding type IV collagen, which is a basement membrane component. Alport syndrome is characterized by a progressive glomerulonephropathy, sensorineural hearing loss and various ocular anomalies. The X-linked form (ATS; MIM 301050) represents about 85% of Alport syndrome cases and is caused by mutations in the COL4A5 gene. COL4A5 encodes the collagen %u03B15 (IV) chain. Most affected males demonstrate macro / microscopic hematuria at an early age and almost all of them develop end stage renal failure later in life. Female carriers may have intermittent hematuria and 30-40% of them have a life-long risk to develop end stage renal disease. High-tone sensorineural hearing loss is estimated to affect 80-90% of males by age of 40 years whereas it is less frequent in females with ATS and tends to occur later in life. Ocular abnormalities are also common and consist of anterior lenticonus, which is virtually pathognomonic for Alport syndrome, cataracts, pigmentary retinal changes (dot and fleck retinopathy) and corneal erosions. Penetrance in X-linked Alport syndrome is estimated to be 0.85 in females and 1.0 in males.