The molecular diagnosis of α-thalassemia is not straight forward and requires resources that are not readily available in many centers. Moreover, in many countries with a high prevalence, it is economically unviable to provide this service to all suspected cases. It is therefore necessary to have a good understanding of the prevalent genotypes and phenotypes, which will facilitate genetic counselling and the identification of patients who really deserve molecular diagnosis. This report is limited to patients who were suspected to have moderate to severe alpha thalassemia based on persistent microcytic, hypochromic anemia, no laboratory evidence of iron deficiency and normal hemoglobin electrophoresis or HPLC. It also included patients with H inclusion bodies and/or H band on HPLC.
Given the selection criteria for screening patients in this study, it is not surprising that only 0.3% were carriers, 38.3% had thalassemia trait and 60.8% had HbH disease. A previous study from Kuwait had shown that most alpha thal carriers had Hb levels >10 g/dl. Therefore individuals with mild microcytosis and hypochromia, but with Hb >10 g/dl and no HbH inclusions or band, should not be considered for molecular diagnosis, but counselling should be offered after screening the family with CBC and HPLC, to rule out b-thalassemia. Resources can then be channeled to individuals with a more severe picture to identify those with HbH disease that need to be followed in the clinic.
The study has revealed the extent of the diversity among individuals with alpha thalassemia in Kuwait. As expected, the vast majority of the patients had the αPA-1 nondeletional allele, which has been reported as the commonest cause of HbH disease in Kuwait and in the region. The frequency of the allele in this study was 0.733. It was found as homozygote in 33.3% of the patients, while heterozygotes accounted for 32.3%. It was present as a compound heterozygote with – α-3.7kb in 20.5% and in combination with other alleles like –MED, -α-5nt, αcd59 and αPΑ-2.
The third most frequent allele in this study turned out to be the α0, --MED, which was found in 13 patients, in whom it presented a HbH disease phenotype in 10. Of the latter, it was in compound heterozygosity with the α2cd19-G in 6 patients from 2 related families, with the – α-3.7kb, in 2 patients, the αIVS1-5nt and the αPA-1 in 1 patient each.
The αPA-1 allele was first described from Eastern Saudi Arabia[10] and previous studies from Kuwait[2, 16] had highlighted its role in the etiology of HbH disease among our patients. It has also been reported as the commonest cause of HbH disease in Saudi Arabia[21], Jordan, [22], Bahrain[23] and UAE[24]. The allele is therefore widespread in the Arabian Gulf, especially in the countries adjoining Saudi Arabia. It is uniformly associated with a moderate thalassemia intermedia phenotype with only occasional blood transfusion requirement, usually with intercurrent infection [16]. HbH disease is mainly a disease of childhood in Kuwait. Most patients are referred to the clinic for investigation of persistent microcytic, hypochromic anemia not responding to iron therapy. Indeed, the anemia tends to improve as the child stops rapid grow the and enters puberty.
This study is the first to report the presence of the α0, –MED allele among Kuwaiti patients. In 3 cases, it was as simple heterozygotes while in 10 cases, it was as compound heterozygotes with the pentanucleotide (5nt) deletion in the αIVS1-5nt in 1, the αPA-1 mutation in 1, the – α-3.7 in 2, and the αcd19 (G/A) in 6 (from 2 related families). In all these instances, the phenotype was mild with moderate anemia. However, in 2 patients with the –MED/ αcd19α genotype, the patients were stunted in growth and were on regular transfusion. The other rare alleles found in the study included the α0 (--FIL) in a Filipino child, HbCS (α2Cd 142 TAA → CAA), Hb Adana (αcd59G/A), αPA-2 (AATAAA®AATGAA), Hb Icaria (αCd 142 TAA → AAA).