PIG-A gene abnormalities in Thai patients with paroxysmal nocturnal hemoglobinuria

Deficient biosynthesis of the glycosyl phosphatidyl inositol (GPI)-anchor in blood cells is implicated in the pathogenesis of paroxysmal nocturnal hemoglobinuria (PNH). Abnormal clonal cells appear in various hematopoietic cell lineages, suggesting that PNH arises as a result of somatic mutation occurred at the multipotential hematopoietic stem cell stage. We previously cloned a gene which is responsible for PNH. The gene termed PIG-A (for Phosphatidyl Inositol Glycan-class A) participates in the early step of GPI-anchor biosynthesis. Studies with cell lines and granulocytes from patients with PNH revealed that in all cases so far characterized, PIG-A is the target for the somatic mutation. In the present study, we analyzed PIG-A abnormality in granulocytes from 14 Thai-patients with PNH. PIG-A RNA was reversed transcribed and the coding region was amplified by polymerase chain reaction and cloned into plasmids. The cDNA thus obtained and genomic DNA were analyzed by mutation detection enhancement gel electrophoresis and sequencing. The assessment of function of PIG-A cDNA was based on the ability to correct the phenotype of a PIG-A deficient cell line after transfection. The result showed that all patients had PIG-A abnormality. Three patients had size abnormality of PIG-A transcripts caused by mutations at the splicing sites in the genomic DNA level. Eleven patients had PIG-A transcripts of normal sizes but had mutations in the coding region which included small deletions and insertions. Taken together with the result from Japanese and British patients, the PIG-A somatic mutations in patients with PNH are small mutations widely distributed throughout coding region and the splicing sites.