An approach for the prevention of thalassaemia in Pakistan

• Main Author: Ahmed, Suhaib
• Published: University College London (University of London) 1998
• Subjects: 610; Mutations
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299931

The basic aim of this thesis was to identify a suitable approach for prevention of thalassaemia in Pakistan. The overall carrier rate for β-thalassaemia was 5.3%. The rate varied by ethnic group, i.e. Punjabi: 4.5%, Pathan: 5.2%, Sindhi: 1.3%, Baluchi: 9% and Mohajir: 5.2%. The annual birth rate of affected children was estimated at 1.35 per 1000. Screening for α-thalassaemia showed 6% carrier rate for α -3.7 genotype. Approaches for identifying carriers and at risk couples were investigated in pregnant females, but proved to be technically difficult and cost ineffective. By contrast screening in ten index families with haemoglobin disorders identified 21-70% (mean 31%) carriers per family. No carrier was identified in five control families without a history of haemoglobin disorder. Follow-up for one year in the families screened showed a significant effect on the marriage choices. Molecular basis of thalassaemia was investigated in 1240 mutant alleles in all ethnic groups. 19 different mutations were found including one novel allele. The five commonest mutations accounted for 81% of the alleles. The pattern of mutations was significantly different in the ethnic groups studied. 7.5% of patients on blood transfusions had thalassaemia intermedia, and its genetic basis included Xmn-1 +/+ genotype (36%) and mild mutations (31%). Coincidental α-thalassaemia was found or suspected in 38% of cases of thalassaemia intermedia. Prenatal diagnosis of thalassaemia was introduced for the first time in Pakistan and in the two years of the study 158 couples used the test. All couples, except two, already had at least one affected child. They had better education and socio-economic status than the controls and 93% requested termination of pregnancy when the fetus was affected. Over 98% of the diagnoses were done by direct mutation analysis. A multiplex polymerase chain reaction for mutation analysis was developed and significantly reduced the total cost and time required for prenatal diagnosis. Consanguineous marriage and recessive disorders were studied in the nine index and the five control families. In 319 couples studied 46% were consanguineous, 52% were Biradri/Tribe members, and only 6% were completely unrelated. Consanguineous marriage (2nd cousins or closer) had increased from 12% in the 1St generation to 45% in the 2nd generation. Antecedent consanguinity had significant effect on the kinship coefficient of the close as well as distant relatives. There was only a marginal difference in coefficient of inbreeding, calculated in a random population sample by conventional methods (0.0257) and by allele frequencies at the D21S11 locus (0.0272). Morbidity and mortality from genetic causes was significantly higher in the children of consanguineous than the non-consanguineous couples living under similar socio-economic conditions. This pilot study appears to have identified a suitable approach for prevention of thalassaemia in Pakistan.