Molecular Genetic Study of Egyptian Hereditary Spherocytosis Patients with Combined Ankyrin-Spectrin Deficiency

Abstract

Hereditary spherocytosis (liS) comprises a heterogeneous group of hemolytic anemia of highly variable clinical expression ranging from an asymptomatic condition to a severe hemolytic disease. liS is the consequence of heterogeneous molecular defects affecting proteins of the red cell membrane namely: (I) combined ankyrin-spcctrin deficiency due to a primary detect of ANK I gene. (2) band 3 deficiency due to dcf(,cls of band 3 gene, (3) protein 4.2 deficiency due to defects of protein 4.2 gene, and (4) isolated spectrin deficiency due to defects of either n-or fl-spcctrin genes. The aim of this work was to identify the underlying genetic defect in 6 Egyptian liS families with diagnosed combined ankyrin-spcctrin deficiency. The ANK I gene was studied using single strand conformation polymorphism (SSCP) analysis followed by nucleotide scq11cncing. An abnormal eonf(mnation was detected in 4 patients by SSCP, one in exon 2 and 3 in exon 6 of ANK I gene. Subsequent nucleotide sequencing revealed no sequence change in exon 2. Exon 6 in the three cases showed a single base substitution of G lo A at position 681 of ANK I gene (6R I CCG->CC:A) with no resultant change in amino acid sequence (silcnl mutation). The frequency of the mutant allele was O.OR. The silent mutation was found in a heterozygote state in the 3 cases. From this study, we can conclude that ankyrin gene mutations are rare in Egyptian HS patients. Subsequent study of other candidate genes (band 3, protein 4.2, and a- and ­ spectrin) is recommended.