Leber Congenital Amaurosis 13 is an inherited retinal dystrophy that is characterized by involuntary movements of the eyes (nystagmus), sluggish pupillary responses, roving eye movement, extreme farsightedness (hyperopia), crossed eyes (strabismus), and sensitivity to light (photophobia). LCA patients may also suffer from keratoconus, a condition where the cornea is abnormally thin and cone shaped. The disorder results in severe visual impairment and electroretinogram studies of affected patients show little to no electrical activity in the retina. A key symptom of the disorder in children is Franceschetti’s oculo-digital sign, a tendency to poke, press and rub the eyes. This often results in deep-set, sunken eyes known as enophthalmus. Other symptoms that can develop include cataracts, glaucoma and corneal problems.
The disorder usually affects children at birth or within the first year of life. LCA affects about 2 to 3 newborns per 100,000 and is one of the most common causes of blindness in children. LCA is diagnosed based on ophthalmological examinations, electroretinogram studies and genetic mutation tests. While there is currently no cure for LCA, the disorder can be managed by the use of low vision optical aids to maximize visual function. Routine ophthalmic follow-ups are also recommended to evaluate the presence of cataract and glaucoma.
Aldahmesh et al. (2009) studied 52 non-syndromic Retinitis Pigmentosa (RP) affected individuals from 17 Saudi families. The patients were diagnosed as having RP based on their gross retinal appearance and a detailed functional assessment. Family histories of all patients were obtained to classify them as sporadic or familial cases. DNA extracted from the patients’ blood samples was used to carry out linkage analysis and homozygosity mapping studies. Known RP genes that overlapped with regions of homozygosity were then screened for mutations. The homozygous RDH12 mutation c.226G>C, resulting in the substitution p.G76R, was found to affect three members of a family. The novel missense mutation was not seen in 100 ethnically-matched controls and affected a highly conserved glycine residue.