Stargardt Macular Degeneration

Stargardt Macular Degeneration, or Stargardt disease is the most common type of inherited macular degeneration. The retina is the lining at the back of the eye. Along with the optic nerve, it forms the ‘nerve’ of the eye. A healthy retina is essential for normal vision. At a cellular level, the retina has 10 layers and the most important of these are the photoreceptors called ‘Rods and Cones’ and the ‘Retinal Pigment Epithelium’. Rods generally help with night vision while cones help with day vision and colour vision. The central retina is called the macula; this area is very rich in cones and a healthy macula is essential to be able to read fine print, identify colours, faces and so on. 

Decreased central vision due to progressive loss of photoreceptors at the macula is the most common complaint in Stargardt disease. Progressive dysfunction of the cones at the macula causes accumulation of a material called ‘lipofuscin’ within the retinal pigment epithelium (RPE). Excessive accumulation of lipofuscin leads to degeneration of the RPE layer  and subsequent loss of overlying photoreceptors.

The affected person notices difficulty in identifying faces or reading. Most of them have reasonable peripheral vision. Symptoms may start in early childhood, although this can vary. As the disease progresses, most people lose a lot of central vision. This is especially difficult in children, since it hampers their school activities. The rate of progression of the disease varies from individual to individual. 

Like other genetic conditions, Stargardt is caused by genetic ‘mutations’. The human  body is made up of millions of cells. The genetic code within each cell is contained in the DNA, with the code being arranged as a set of spellings (Nucelotides). These nucleotides get together to form amino acids, which then form proteins. Proteins are essential for every single function within the human body. When an error occurs in these nucleotides (like the spelling mistakes within a word), a mutation occurs. A mutation that affects the normal functioning of the retina can lead to genetic conditions like Stargardt disease. 

Stargardt disease is mostly caused by a mutation in a gene called ABCA4. This is transmitted in an autosomal recessive manner while rarely it is transmitted in an autosomal dominant manner. 

In autosomal recessive disease, each parent carries one copy of the mutated gene (while the other gene is normal). They have no symptoms themselves and are unaffected carriers of the mutation. When such a couple has children, there is a 50% chance that the child inherits one affected copy from one of the parents (while the other copy is normal). This child then becomes an unaffected carrier. 25% of the children however can inherit both the abnormal copies, and they then develop the disease.

In autosomal dominant disease, one of the parents is already affected and carries a single copy of the mutation. 50% of the children may inherit the same and develop the disease.

Genetic testing is available to help identify the mutation in a given individual/family. Identifying the causative mutation helps in several ways. The affected individual is able to understand the various treatment approaches under research and the appropriate clinical trial. It may also help understand the severity/progression of the disease. The affected family will be able to understand the implications for future progeny. Appropriate genetic counseling and testing can reduce the risk of the disease being transmitted to the next generation.  

Although Stargardt is currently incurable, research into treatment has galloped worldwide. There are several clinical trials that include gene therapy and cell replacement (stem cell) therapy.

Appropriate use of low vision aids and rehabilitation can help people with Stargardt disease significantly. This is especially true for children who have to carry out school activities. Along with FORUS, CEGR has developed and deployed a device called “LUMINO” that can be used for academic activities in the classroom.