A family study of HbS in a Malay family by molecular analysis

ABSTRACT

Sickle cell disease (SCD) is an inherited red cell disorder, characterized by the tendency of haemoglobin S or sickle haemoglobin to polymerize and assume a characteristic sickle shape. Molecular analysis has been the mainstay of detection method when confirmation is required. Previously a polymerase chain reaction (PCR)-based restriction enzyme analysis was used for this purpose. A simple bidirectional allele-specific amplification, recently described by Waterfall in 2001 was used to detect the GAG --> GTG mutation on codon 6 of the beta globin gene. Two sets of primers for the mutant and the wild type alleles were used in a single PCR reaction to amplify the regions of interest. The resultant PCR products will produce two fragments at 517 and 267 base pair (bp) respectively. This report highlights the investigations for SCD in the family of a 16-year old girl with recurrent painful crisis affecting the lower limbs whereby the family members are asymptomatic for the disease. Her haemoglobin electrophoresis at an alkaline pH showed dense bands at the HbS and HbF regions, while her father and two sisters had bands at HbS, HbF and HbA. The PCR analysis showed that she was homozygous for the mutation by the presence of only one band at 267 bp fragment, while the father and her sisters were heterozygotes, with the presence of two bands at 267 as well as 517 bp fragments. DNA sequencing of the sample confirmed the mutation. In conclusion, this case report highlighted the simple and cheap yet practical method for molecular confirmation of the presence of HbS gene in subjects with homozygous or heterozygous state of the condition.