Phenotypic and genotypic expression of alpha thalassaemia in Ibadan, Nigeria.

BACKGROUND

Alpha thalassaemia is a common monogenic disorder found in most parts of the world but the severe form is restricted in its distribution while the mild deletional form of alpha- thalassaemia has a wider geographical distribution.

METHODS

One hundred and fifty one Nigerians which included 29 patients with unexplained recurrent haemolytic anaemia had their a-thalassaemia status determined by gap PCR after being screened using red cell indices.

RESULTS

Only the -alpha(3.7) deletion occurs among Nigerians with a gene frequency of 0.21. Forty-two per cent of the study population are heterozygotes, 9% are homozygotes while 49% are normal for this deletion. The mean haematocrit for the study population is 37.5%: homozygote, heterozygotes and normal subjects had a mean haematocrit of 37.3%, 37.5% and 37.7% respectively. The mean mean corpuscular haemoglobin (MCH) and haematocrit are significantly lower for patients than controls (24 +/- 2.9 pg vs. 26.6 +/- 2.5 pg (p = .000), 29% vs. 40% (p = .000) respectively). Forty three percent of both patients and controls had MCH of less than 27 pg but only 10% of patients had MCH that is greater than 27pg. Homozygote patients had a higher mean haematocrit than patients who are normal for the deletion (34.7% vs. 25.4%, p = 0.06) but homozygote patients had a lower mean haematocrit than homozygote controls (34.7% vs. 38.5%, p = 0.4).

CONCLUSION

This would suggest that alpha-thalassaemia is not responsible for the recurrent haemolytic anaemia observed in these patients and that the high prevalence of microcytosis among the normal populace needs further exploration.