XL dominant Alport Syndrome: a rare condition and a rare mode of genetic transmission
Alport syndrome (AS) is a rare abnormality of glomerular basement membrane caused by mutations in several different genes, all of which encode particular forms of type IV collagen, a major component of basement membrane. It is characterized by chronic renal failure leading to end-stage renal disease (ESRD) and is often associated with sensorineural deafness (Kanski 2003). The inheritance is typically XL dominant (about 80-85%) although autosomal recessive and autosomal dominant cases have been reported (Ermisch, Gross et al. 2000). The typical ocular signs are anterior lenticonus and scattered, pale, yellow, punctate flecks in the peri-macular region, sparing the fovea with normal visual acuity (Kanski 2003).
The X-linked form of the disease is caused by mutations in the COL4A5 gene encoding the alpha5-chain of type IV-collagen (Hertz, Juncker et al. 2001) whereas the autosomal forms are due to mutations in the COL4A3 or COL4A4 genes (Gubler, Knebelmann et al. 1995). The ocular manifestations of autosomal recessive Alport syndrome are probably identical to those for the X-linked form; although the mutations in these diseases affect genes for different type IV collagen chains, these chains occur together in the basement membranes of the kidney, eye and ear, and abnormalities in any one may result in the same clinical phenotype (Colville, Savige et al. 1997).
With respect to the prognosis of AS patients, males usually develop end-stage renal disease if not treated, whereas female patients have more variable phenotypes ranging from asymptomatic hematuria to ESRD. The variable phenotypes in female patients may be attributable to different X-chromosome inactivation patterns (Nakanishi, Iijima et al. 1998). A 15 year longitudinal study of patients with AS had two cases progress to renal failure at 15 and 21 years respectively, while 26 patients had normal renal function within the second decade of life (Genova, Polisseni et al. 1986). The prognosis of males is improved by angiotensin converting enzyme inhibitors (ACE inhibitors) to protect kidney function although it appears to only be useful if treatments instigated in childhood (Proesmans and Van Dyck 2004) and ESRD can be treated by kidney transplant (Imai and Isaka 2004).
A 19 yr old Caucasian male presented to the Queensland University of Technology Optometry Clinic complaining of monocular and binocular diplopia, which he had had for several years. He had been diagnosed with Alport syndrome ??? months earlier at the a clinic in Switzerland. He was wearing a hearing aid but didn't have any kidney problems although he was taking blood pressure medication with the aim of preventing kidney damage. He reported that squinting sometimes reduced the diplopia and that his right eye was worse than his left. His maternal grandfather had died from kidney failure, his mother has kidney problems and high blood pressure and his mothers' nephew is suspected of having AS also.
His current specs were 18 months old with R 4.00/-2.00 x 175, L 2.75/-1.00 x 120. Vision with these was R 6/10 L 6/10-2 OU 6/8.5- which wasn't improved after subjective refraction. Auto refraction gave R 1.75/-4.25 x 175, L 2.50/-4.75 x 5 which was not tolerated by the patient. Slit lamp examination revealed anterior lenticonus, accounting for the diplopia and high astigmatism in his auto refraction prescription. The patient was advised that lens extraction surgery could improve his vision although he met the visual qualifications for a driving licence in Queensland.
An appointment was made 27 months later to recheck his prescription although in the time between this appointment and the first, he had had new spectacles made up at another optometrist with R 1.75/-1.50 x 18, L 1.75/-1.25 x 115 which gave him visual acuity of R 6/18-1 L 6/18 OU 6/12-2. An...