Investigation on mutation of galactose-1-phosphate uridyl transferase enzyme in patients with congenital cataracts

Galactose is a monosaccharide with a structure containing the aldehyde group and six carbon atoms. It is the fourth carbon epimer of glucose. The main sources of galactose are milk and milk products, and after intestinal absorption it is metabolized in the liver. There are four enzymes in the Leloir pathway for galactose metabolism: Galactose mutarotase (GALM), Galactokinase (GALK), galactose-1-phosphate uridyl transferase (GALT) and uridine diphosphate galactose-4-epimerase (GALE). Classical galactosaemia is an autosomal recessive inherited metabolic disorder due to deficient GALT and it causes jaundice, vomiting, growth retardation, cataract, coma, sepsis and could be fatal. The gene encoding GALT is located on chromosome 9p13 and spans 4.3 kb of DNA arranged into 11 exons. Over 180 different base changes and diseasecausing mutations have been reported in the GALT gene. Q188R is a mutation where arginine amino acid is replaced with glutamine and is the most common in north European populations and those predominantly of European descent.Congenital cataract is the most important cause of curable blindness in children. Infantile cataract occurs, in general, due to genetic or metabolic diseases, intrauterine infections, and trauma. With GALT enzyme deficiency, high amounts of Gal-1-P accumulates in the blood and by transforming into galactitol causes cataract formation which is reversible at first. GALT deficiency is considered as a risk factor for cataract formation. After diagnosing galactosemia and stopping the intake of galactose, symptoms begin to subside.In this study, GALT enzyme mutation is investigated for galactosemia disease in 33 children who are diagnosed with congenital cataracts and therefore operated in Ophthalmology Clinic of Dicle University Faculty of Medicine, and in the healthy subjects of the same number. As a result, we found two children (% 6) with homozygotes for Q188R mutation in GALT gene among the incongenital cataract study group.In children with Q188R mutation, due to not being diagnosed as galactosemia in newborn period and thus failing to apply necessary galactose restricted diet, developed cataracts irreversibly. Therefore, ophthalmologists need to think about the presence of metabolic disease in patients with congenital cataracts. Having stated this fact, we think it would be useful for public health to generalize galactosemia screening along with other metabolic diseases such as PKU, Biotinidase deficiency etc. in newborn period.