NEONATAL SCREENING AND MOLECULAR GENETIC CHARACTERIZATION OF GLUCOSE- 6-PHOSPHATE DEHYDROGENASE DEFICIENCY IN ALEXANDRIA

Abstract

Glucose-6-phosphate dehydrogenase deficiency is the most common human enzymopathy, affecting more than 400 million people worldwide. G6PD is a housekeeping enzyme critical in the redox metabolism of all aerobic cells with special importance in red blood cells. Although, most G6PD deficient individuals are entirely asymptomatic and develop symptoms only in response to oxidant stress, some of the clinical manifestations associated with G6PD deficiency are serious as neonatal jaundice which may lead to death or kernicterus.

G6PD gene is located in q28 region of the X chromosome. It consists of 13 exons and 12 introns distributed over approximately 20 kb of genomic DNA. Polymorphisms of the G6PD gene are numerous with most mutations identified are point mutations causing single amino acid substitution in the G6PD gene. One hundred forty variants were characterized at the DNA level. Generally mutations are limited to contiguous geographical areas or areas where population migrations are well documented.

G6PD deficiency can be diagnosed in hemizygote males and homozygote females by semi-quantitative methods or quantitative assay of the enzyme activity, both methods can't accurately distinguish heterozygote females, which is best identified by detection of mutation in genomic DNA. The most effective management of G6PD deficiency is to prevent haemolysis by avoiding oxidative stress. In a population with high prevalence rate, early detection of the enzyme deficiency by neonatal screening is desirable in order to take appropriate measures to prevent the complications of hemolysis and jaundice.

This study aimed at screening newborn infants for G6PD deficiency to allow early detection of the disease and estimate the prevalence of G6PD deficiency among neonates in Alexandria. Also it aimed at detecting the G6PD gene alleles; Mediterranean (C563T) and A- (A376G/G202A) and their frequencies and identifying the heterozygote carriers among available females in each family, at gene level. Finally, it aimed to offer proper genetic counseling for G6PD deficient patients and their families.

The present study was conducted on 1100 leftover bloodspots on filter paper cards collected by means of heel prick for the "National Program of Neonatal Screening for Congenital Hypothyroidism" in Alexandria. All these neonatal blood samples were screened for G6PD deficiency using the fluorescent spot test. All G6PD deficient newborns were recalled and subjected to confirmation of the detected result.

Those confirmed G6PD deficient neonates together with another 10 G6PD deficient patients referred from Al-Shatby Pediatric University Hospital were subjected to careful history taking and clinical genetic examination. Both groups were included in the molecular study using PCRIRFLP technique for detection of the three common G6PD gene mutations; C563T, A376G and G202A, and identification of heterozygote carriers among available female relatives of cases