Newborn screening for G6PD deficiency is performed routinely in Malaysia because of our high disease prevalence. The World Health Organization recommends screening all newborns in populations with a prevalence of 3 to 5 percent or more in males.

Neonatal hyperbilirubinaemia (severe jaundice) incidence is twice that of the general population in males who carry the defective gene and in homozygous females. It rarely occurs in heterozygous females.

G6PD deficiency is common in Malaysia and was shown to be more prevalent among Malays and Malaysian Chinese descents, and less common among the Indians. Overall incidence of neonatal jaundice in Malay G6PD-deficient neonates was 82.6% (71 of 86). 80% of the neonates with jaundice require phototherapy and a small percentage requires transfusion.

G6PD deficiency has been shown to be an important cause of severe hyperbilirubinaemia and kernicterus (bilirubin-induced brain dysfunction) necessitating a national screening program for G6PD deficiency for newborns in all state hospitals, a program that has been in place for the last twenty years in Malaysia.

1. Definition of G6PD Deficiency

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a genetic disorder where a person has a lower than normal level of this red blood cell enzyme. Red blood cells carry oxygen from the lungs to tissues throughout the body. This enzyme helps red blood cells work properly and keep them intact by reducing oxidative stress from accumulation of harmful oxygen species during normal metabolism.

When people with G6PD deficiency are exposed to stresses such as infections, certain drugs and substances and ingestion of fava beans (broad beans), it can increase the levels of reactive oxygen species causing premature breakdown of red blood cells (haemolysis).

These drugs / substances include:

1. Antimalarial drugs (primaquine, pamaquine, and chloroquine)
2. Aspirin
3. Sulfonamides
4. Nitrofurantoin
5. Nonsteroidal anti-inflammatory drugs (NSAIDs)
6. Quinidine
7. Quinine
8. Napthalene (moth balls)
9. Non-sulfa antibiotics
10. Henna

Breastfeeding mothers with G6PD deficient baby should abstain from ingesting these substances as they will be present in small amount in breast milk and consumed by the baby.

People with this condition may be affected by the following medical conditions:

1. Haemolytic anaemia
2. Prolonged neonatal jaundice (leading to kernicterus)
3. Favism

Haemolytic anaemia leads to paleness, yellowing of the skin and the whites of the eyes (jaundice), dark urine, fatigue, shortness of breath, enlarged spleen and a rapid heart rate.

Favism may be defined as a haemolytic response to the consumption of fava beans. All individuals with favism show G6PD deficiency. However, not all individuals with G6PD deficiency exhibit favism. Favism is known to be more prevalent in infants and children and G6PD genetic variant can influence chemical sensitivity.

Genetics

G6PD deficiency is a significant cause of mild to severe jaundice in newborns. The disease is caused by a mutation on the gene coding for G6PD enzyme.

G6PD deficiency tends to affect males as the gene is located on the X chromosome, which is one of the two sex chromosomes. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. Females, having two copies of the X chromosome, are less affected because a mutation would have to occur in both copies of the gene for the disorder to manifest. A significant characteristic of X-linked inheritance is that fathers cannot pass these traits to their sons. Offsprings will inherit the defective G6PD gene from their mothers (carrier).

Most individuals with G6PD deficiency will not show any symptom. Although symptomatic patients are almost exclusively male due to the X-linked pattern of inheritance, female carriers can be clinically affected. A female with one affected X chromosome (heterozygous) will show the deficiency in approximately half of her red blood cells. In rare cases however, including double X deficiency, the ratio can be much more than half, making the individual almost as sensitive as a male.

Prognosis & Complications

The usual outcome from a haemolytic episode is spontaneous recovery from the crisis. Mental retardation in newborns can occur if they are left untreated. Rarely, kidney failure or death may occur following a severe haemolytic event. G6PD deficient individuals must strictly avoid substances that can trigger such episode.

Treatment may involve:

1. Medicines to treat an infection, if present
2. Stopping any drugs that are causing red blood cell destruction
3. Phototherapy to reduce bilirubin level
4. Exchange transfusions, in some cases

2. Prevalence in Malaysia

An estimated 400 million people worldwide have G6PD deficiency. This condition occurs most frequently in certain parts of Africa, Asia, Middle Eastern and the Mediterranean.

In Malaysia, the prevalence of male G6PD deficiency were 4.6%, 6.0% and 1.3% in the Malays, Chinese and Indians respectively while it is significantly lower in females at 1.4%, 1.65 and 0.49% respectively. A study on the Malaysian Orang Asli stated a high prevalence of 9.0% in the Negrito tribe.

3. How It Is Diagnosed

Testing for G6PD deficiency should be suggested when an acute haemolytic reaction occurs that is precipitated by exposure to a known trigger, either in children or in adults, particularly if they belong to the affected ethnic groups. Moreover, members (especially males) of families where jaundice and splenomegaly are recurrent should be tested for G6PD deficiency. Newborn babies with severe prolonged neonatal jaundice, those belonging to Mediterranean or African ancestry in particular, are quite likely to have G6PD deficiency.

A direct test for G6PD is the Beutler fluorescent spot test. Other possible diagnostic tests include determination of enzyme activity, direct DNA testing and sequencing of the G6PD gene.

4. Sample Collection: Filter Paper

Whole blood is collected and blotted onto a filter paper to be analysed in the laboratory. Disk cut-out of the dried up blood is immersed in working solution to detect the production of NADPH (nicotinamide adenine dinucleotide phosphate).

5. Method Used

In Malaysia, the most common method to screen for G6PD Deficiency is through a simple fluorescent spot test. This semi-quantitative test is simple and inexpensive to be employed in screening every newborn in the country. The test visually identifies a substance called NADPH (Nicotinamide Adenine Dinucleotide Phosphate) produced by G6PD enzyme under long wave ultraviolet light. When the blood spot does not fluoresce, the test is positive for G6PD deficiency.

6. Result Interpretation

Samples with normal or slightly depressed G6PD activity will show strong fluorescence. When the blood spot does not fluoresce, the test is positive for G6PD deficiency. No fluorescence suggests complete lack or marked deficiency of G6PD.

Test limitations

The result can be falsely negative in patients who are actively haemolysing. It can therefore only be done 2–3 weeks after a haemolytic episode.

This test is clinically significant only after 30 days of blood transfusion, as the donor’s blood will exhibit normal G6PD activity within a number of days from the transfusion.

Female heterozygotes may be difficult to diagnose because of X-chromosome mosaicism leading to a partial deficiency that will not be detected reliably with screening tests; this leads to diagnostic challenge.

A considerable number of partially G6PD deficient female neonates (heterozygotes) are undetected and classified as having normal enzymatic activity using the semiquantitative method. For this group, a different testing method is advisable to assess their G6PD status.

References

1. Ainon, O. (2004). Complete molecular characterisation of glucose-6-phosphate dehydrogenase (G6PD) deficiency in a group of Malaysian Chinese neonates. Malaysian J Pathol ; 26(2) : 89 – 98.
2. Amini, F, Ismail, E, Zilfalil, BA. (2011). Prevalence and molecular study of G6PD deficiency in Malaysian Orang Asli. Intern Med J. 41(4):351-3.
3. Alex, T, Balakrishnan, S, Zamri, A. (1989) Hyperbilirubinaemia And Erythrocytic Glucose 6 Phosphate Dehydrogenase Deficiency In Malaysian Children. Med. J. Malaysia Vol. 44 No. 1.
4. Ainoon, O, Yu, Y.H. Amir Muhriz, A.L., Boo, N.Y., Cheong, S.K. & Hamidah N.H. (2002) Glucose-6-Phosphate Dehydrogenase (G6PD) Variants in Malaysian Malays. Human Mutation: Mutation in Brief #574.
5. Minucci, A, Giardina, B, Zuppi C, & Capoluongo, E. (2009) Critical Review: Glucose-6-phosphate Dehydrogenase Laboratory Assay: How, When, and Why? IUBMB Life, 61(1): 27–34.
6. Ainoon, O, Alawiyah, A, Yu, YH, Cheong, SK, Hamidah, NH, & Boo NY, et al. (2003) Semiquantitative Screening Test For G6PD Deficiency Detects Severe Deficiency But Misses A Substantial Proportion Of Partially-Deficient Female. Southeast Asian J Trop Med Public Health Vol 34 No. 2.
7. Randox Laboratories Limited, United Kingdom. G6PD Manual Screening test product insert.