Although cataracts are commonly associated with the elderly population, some cataracts are congenital in nature, occurring with birth due to a genetic abnormality. Similar to “normal” cataracts, congenital cataracts are characterized by clouding of the eye’s lens, but the clouding is mainly due to a metabolic disorder that develops when the child is a fetus.
With genetics playing a key role in the development of congenital cataracts, families are affected by the condition. Such was the case for a four-generation ethnic Han Chinese family studied by researchers at The First Affiliated Hospital of Zhengzhou University in China. Unique to this family compared to other families or individuals with congenital cataracts was the specific genetic mutation leading to their cataracts. The authors, writing in the journal Genetics and Molecular Research, published the case study under the title “A Novel 3-Base Pair Deletion of the CRYAA Gene Identified in a Large Chinese Pedigree Featuring Autosomal Dominant Congenital Perinuclear Cataract.”
Immediately in the study of this family, the researchers ruled out other concomitant disorders that may be leading to their cataracts. Full clinical and ophthalmolgic examinations were unremarkable, so blood samples were obtained from the family. From blood samples, the researchers extracted DNA and discovered a novel mutation in the gene alpha A crystallin (CRYAA)–no other laboratories had previously found this mutation in association with congenital cataracts.
To explore the consequences of the mutation, the researchers fully sequenced the CRYAA gene. The mutation occurred within a DNA region that was essential for coding the correct amino acid sequence for the alpha A crystallin protein. Alpha A crystallin is found within the lens and cornea of the eye and allows for the transparency of the lens. Evidently, mutations in this protein may cause protein aggregation and cataract development, in light of the suggested role for alpha A crytallin in preventing cataracts.
Adding onto the novelty, the researchers also conducted a prenatal diagnosis for a fetus that was going to be born to the family. “This is also the first report of prenatal diagnosis of this type of congenital cataract,” stated the authors. The fetus did not have the mutation and was healthy for at least a year after the appointment. Healthy and unaffected individuals do not have this mutation, making the case specific to CRYAA and congenital cataracts.