Glucose-6-Phosphate Dehydrogenase (G6PD) gene is located at the X-chromosome at 
Xq28 and the disease is recessively inherited predominantly in males. More than 
400 variants have been proposed based on clinical and enzymatic studies. The aim 
of the current study was to identify C563T mutation in G6PD-deficient newborns 
and to correlate the enzyme residual activity with the presence of the mutation. 
Some 1189 full-term neonates aged 3-5 days old were tested for G6PD activity in 
dried blood spots from Guthrie cards using a commercial kit. DNA extraction from 
Guthrie cards and mutation identification among the deficient samples were 
performed with current techniques. A total of 92 (7.7%) newborns were 
G6PD-deficient. In 46 (50%), the mutation C563T was identified. The residual 
activity in C563T hemizygote males (n = 28) was statistically significantly 
lower (1.23 ± 0.93 U/g Hb) than that in non-C563T G6PD-deficient males (n = 25) 
(4.01 ± 1.20 U/g Hb, p < 0.0001) and in controls (13.6 ± 2.9 U/g Hb, p < 
0.0001). In C563T heterozygote females, the estimated enzyme activity was lower 
than that determined in non-C563T females. Male C563T hemizygotes suffer from 
G6PD deficiency and severe neonatal jaundice. G6PD activity showed statistically 
significant correlation with total bilirubin blood levels.