Stargardt’s Macular Dystrophy

Stargardts

Cone Rod dystrophy

Retinitis Pigmentosa (RP)

RP19

Stargardt’s disease (SD) is one of the most common serious eye diseases in children and young adults, striking one in 10,000. Stargardt’s disease (SD) can occur in any genetic pattern of inheritance (e.g., Dominant, Recessive, X-linked). SD is a disease of the retina – the thin membrane covering the back inner part of the eye. The retina, which contains the photoreceptors of the eyes, as well as the retinal pigment epithelium (RPE) may be affected in SD.

A person with SD may first notice blurring of vision or sensitivity to lights, like a car’s headlights, or notice reading becoming difficult.  Faces become difficult to identify and driving becomes more difficult. If patients have the onset of SD early, vision may deteriorate faster than if SD develops later in life (e.g., late 20s). Patients that develop SD later in life reveal a slower developing disease in terms of visual acuity at least. But patients that develop SD later in life have more problems in terms of adjusting to life with reduced vision and even blindness (visual acuity worse than 20/200). Older patients with SD are more likely to be depressed. Availability of quality health care is one of the major concerns of those with SD.

In term of genetics of the disease,SD is well interesting to say the least. It has been known for some time that SD and Fundus Flavimaculatus (FF), another retinal disease, share a number of similar characteristics. For example, both diseases can cause abnormalities in pattern ERG, flash ERG as well as electrooculogram (EOG; although more rare in SD).  Both may present as normal or near normal retinas and with and without “flecks”.  Most recently, genetic studies have “proven” that SD and FF share the same areas of gene abnormalities, known as ABCR4 – a mutation in a retina-specific ATP binding cassettee transproter gene (a what?)…We’ll call it a gene defect. Any ways, as it turns-out this ABCR4 gene defect or actually I should say gene defects, now accounts for a number of human retinal diseases including certain types of retinitis pigmentosa (recessive RP, RP19) and even some forms of Age-related Macular Degeneration (AMD) as well as cone rod dystrophy. No kidding; see van Driel et al (1998, Ophthalmic Genetics 117-22). Now they’re calling all these related retinal diseases – as ABCR or ABCA mutations and the degree of remaining function of the gene also determines the severity of the disease. Get this; one family had a mother with SD while her son had RP. The gene work showed that she had one type of ABCA4 gene mutation while the son had a nearby gene mutation (Exon 42 vs Exon 43, like next door neighbors).

How bad does vision get in SD? The may be two types of SD at least in terms of visual acuity and its progression (e.g., Kim and Fishman, 2006): In type I disease, almost everyone has 20/200 or better visual acuity. Also, they’re more likely to maintain their visual acuity over time. Now 20/200 visual acuity is still considered legal blindness but you can do a heck of a lot (i.e., almost everything) with 20/200 visual acuity. OK, so you can’t drive a commercial plane or a commercial truck, I don’t either.

In type II disease, visual acuity was 20/200 or better in about 83% of patients with SD and in almost everyone visual acuity was 20/400 or better in at least one eye (94%).