Four Novel Deletions in Globin Genes Revealed by Multiplex Ligation Dependent Probe Amplification Assay (MLPA) Technology.

Abstract

For nearly 2 decades, the Hadassah Hospital hematology laboratory has been performing DNA-based diagnosis of thalassemia patients and carriers of alpha and beta thalassemia trait. Despite exhaustive analysis using conventional methods, no mutation or deletion could be identified for several families. Recently, MLPA technology was successfully applied to the diagnosis of deletions of alpha and beta globin genes (Harteveld, 2005). This method uses 2 sets (of 35 and 50 probes) covering 700 kb of alpha-globin and 500 Kb of beta-globin, respectively. In the current study, we applied this technology to the analysis of four additional families. Three are Ashkenazi Jews with suspected thalassemia trait. The fourth is a Persian Jewish patient with HbH disease who was only found to have -α 3.7, with an unknown deletion of two alpha genes on the other chromosome. Hematological data are presented in Table 1. MPLA analysis revealed that three of the propositi (2 of the Ashkenazim and the Persian patient) carried large deletions of the alpha globin locus and the third Ashkenazi family carried a large deletion of the beta globin locus, all of which are previously undescribed. Family C was found to have a deletion encompassing a region upstream of the alpha globin cluster but the alpha-like genes are all present. Family K has a large deletion removing the entire alpha globin cluster. The Persian patient has a large deletion of 2 alpha globin genes. Lastly, Family M, of Ashkenazi origin, carries a large deletion of the beta globin cluster whose 5′ end has not yet been mapped. Notably, this family has no elevation of HbA2 or HbF to indicate that they carry beta-thalassemia trait. We conclude that, while large deletions of the alpha or beta globin cluster are not common, they can present a serious problem in diagnosis, potentially leading to erroneous genetic counseling. Identification of such deletions can allow accurate genetic counseling and prenatal diagnosis in appropriate families. MPLA technology is invaluable in characterizing these types of deletions which escape detection using more conventional techniques.Hematological data of Patients and FamiliesName, Ethnicity (sex, age)RBCHbMCVMCHRDWHb EPFamily C, AshkenaziFamily C Mother (34y)4.011.48728.514.3Family C Father (38y)6.0813.57122.215.7Family C Child I (F, 8y)5.5111.16320.114.8Family C Child II (M, 6y)5.9111.96520.115.9Family C Child III (F, 2.5y)4.1111.584.627.716.1Family K, AshkenaziFamily K Propositus (M, 31y)6.6314.169.421.314.9Family MF, PersianFamily MF Propositus (M, 37y)5.519.756.717.523.7HbH 6%Family M (beta thal), AshkezaniFamily M Mother (38y)5.4610.763.919.614.8HbA2 2.8%Family M Father (51y)5.0713.380.326.213.2HbA2 2.2%Family M Child I (F, 17y)4.8514.286.729.312HbA2 2.6%Family M Child II (F, 13y)5.4310.662.319.514.8HbA2 2.5%Family M Child III (F, 11y)4.4312.283.427.412.7HbA2 2.4%Family M Child IV (F, 4y)6.3211.256.717.716.5HbA2 2.5%