The first use of EaeI restriction enzyme in DNA diagnosis of Hb Q-India

The α-chain variant Hb Q-India (c.193G>C) is caused by a point mutation GAC→CAC at codon 64 of the α1 globin gene and is clinically silent. Point mutations can be diagnosed easily by many simple polymerase chain reaction (PCR) techniques including PCR-restriction digest, but for Hb Q-India the restriction digest has never been described. In this work we aimed to develop a restriction enzyme digestion assay for DNA diagnosis of Hb Q-India, in order to increase the panel of restriction enzymes used in DNA diagnosis of haemoglobinopathies and also as a simple cheap alternative to the ARMS-PCR method.

A restriction enzyme digestion assay was designed for diagnosis of Hb Q-India using the restriction enzyme EaeI enzyme as the Hb Q-India mutation abolishes the recognition site of this enzyme. Patients were screened for an abnormal haemoglobin by high performance liquid chromatography (HPLC) and those had an abnormal peak with a retention time between 4.7 and 4.8 minutes were selected for diagnosis at the molecular level. The α1 globin gene was amplified in 12 cases with a presumed diagnosis of Hb Q-India by HPLC and isoelectric focusing (IEF), and the amplified products were subjected to the EaeI digestion.

All the 12 cases were diagnosed positive (100%) for Hb Q-India by the EaeI restriction enzyme digest. They were heterozygotes for the mutation.

EaeI restriction enzyme digestion can be used as a simple and robust alternative method to ARMS-PCR for DNA diagnosis of Hb Q-India. The EaeI restriction enzyme can be added to the panel of restriction enzymes used in the DNA diagnosis of the abnormal Hb variants. Concomitant use of HPLC and IEF can be used efficiently for presumed diagnosis of this rare variant.