GSTM1 and anemia (phenotype): In general anaemia was mild, however in one child from the high risk group ZDV prophylaxis was discontinued at the age of 5 weeks due to decreased haemoglobin concentration (Hb at the age of 2 weeks 14.4 mg/dl, 1 month 7.8 mg/dl, 3 months 11.9 mg/dl).