In conclusion, the present study demonstrates that highreticulocytosis in neonate blood does not bias measurement ofenzyme activity in G-6-PD-deficient neonates. In addition, the highprevalence of G-6-PD variants associated with low activity (WHO classII G-6-PD type), in conjunction with mosaicism of X-chromosomeinactivation could result in female heterozygous neonates with suchgenotypes having G-6-PD activity falling either in (low) normal ordeficiency range, and only genotyping would permit detection ofheterozygotes carrying these variants among those with G-6-PD-normal phenotypes