A New β0-Thalassemia Mutation (codon 102, AAC>ATCAC) in Coexistence with a HeterozygousP4.2 NipponGene

Abstract

A new β-thalassemia (β-thal) frameshift mutation was found at codon 102 (AAC>ATCAC) in a 17-year-old Japanese male and his 14-year-old sister. Both demonstrated a more severe phenotype than the usual β-thal minor with mild hemolytic involvement. No mRNA derived from the thalassemic allele, or β^TmRNA, was detected in the sequencing analysis of the whole mRNA (cDNA). However, the β^TmRNA from the whole βmRNA was specifically amplified by amplification refractory mutation system (ARMS), and was actually found to be present. Furthermore, quantitative polymerase chain reaction (q-PCR) demonstrated a negligible amount of β^TmRNA. Thus, their more severe phenotype was not caused by the “dominant type” β-thal in which a considerable amount of the β^TmRNA would be expected. In fact, our proband had a total βmRNA level that was mostly normal. Thus, the cause of a β-thal phenotype by the frameshift mutation was ascribed to the reduced amount of mRNA. We further searched for the cause of their severe phenotype. However, factors that exacerbated the phenotype of β-thal, such as α-globin gene triplication, coexisting iron deficiency and infection were not found. Finally, we noticed that the red cell morphology revealed ovalocytosis and small numbers of stomatocytes that were seen in the hereditary spherocytosis (HS), especially by P4.2 mutations. The sequence of the P4.2 gene disclosed heterozygous P4.2 Nippon, or missense mutation at codon 142 (GCT>ACT) on exon 3, the most common mutation of Japanese HS. Frequent mutations of other membrane proteins, Band 3 and ankyrin that are common cause of HS in the Japanese population, other than P4.2, were not detected. When HS by P4.2 Nippon develops it is homozygous, and no P4.2 protein is observed in sodium dodecilsulphate-polyacrylamide gel electrophoresis (SDS-PAGE), while in our case the amount of the P4.2 was almost normal in the SDS-PAGE. However, there are several reports that revealed more severe phenotypes of β-thal by the coexisting abnormality of membrane protein. It is uncertain, but the presence of heterozygous P4.2 Nippon may be associated with the exacerbation of the phenotype of β-thal minor.