Screening for an enzyme defect in newborns

Known as the most common enzyme defect in humans, glucose-6-phosphate dehydrogenase (G6PD) deficiency is an inherited condition that affects more than 300 million people worldwide. Early detection of the disorder is vital, as newborns are vulnerable to its symptoms, including jaundice and anaemia, which can be life threatening.

In Saudi Arabia, screening is typically done by taking blood samples fromthe arms or legs. But blood taken from the umbilical cord immediately after birth is increasingly viewed as a preferable option, as it is easier to collect and does not cause the child or mother unnecessary pain.

However, since infants undergo many physiological changes that might affect G6PD activity soon after birth, it was unclear how effective cord blood could be in detecting the disorder.

A large-scale retrospective study of children born in Saudi Arabia from January to December 2008 sought to reveal an accurate picture of the validity of cord blood screening for G6PD deficiency. Two per cent of the 8,139 newborns from whom cord blood was taken had G6PD deficiency. Boys were significantly more affected than girls, at a ratio of almost 4:1. Just over one thousand of the newborns had samples taken both from the umbilical cord and from the arms or legs. Results from the samples were compared and suggest that cord blood is just as effective as peripheral blood in detecting G6PD deficiency.

Cord blood sampling notably led to fewer false negative results, reducing the risk of missing a G6PD deficiency diagnosis. The team of researchers, including KAIMRC senior research scientist, Mohammed Al Balwi, concludes that the study reinforces the practice of using cord blood for newborn screening.

The fact that 79% of those affected in the study were males concurs with the consensus that they are more at risk of the condition. The defective gene is carried on the X chromosome. Since males have just one X chromosome, a single altered gene may cause G6PD deficiency. Females, who have two X chromosomes, usually become carriers without showing signs of the defect.

The World Health Organization recommends neonatal screening in areas with a prevalence of over 3% in males. Although figures vary widely by region, the Middle East has one of the highest prevalence estimates of G6PD deficiency in the world at six per cent. For males alone this figure is 7.2%.

As yet, there are no treatments for G6PD deficiency. It is a lifelong condition requiring avoidance of certain foods and medicines, such as fava beans and antimalarial drugs. The present study may serve as a basis for further surveys tracking G6PD enzyme levels in older children and adults.