Alpha thalassemia deletions found in suspected cases of beta thalassemia major in Pakistani population.

BACKGROUND & OBJECTIVE: Alpha (α) thalassemia is a hereditary disorder and is caused by deletions or mutations in globin genes. It is present in two clinically significant forms: hemoglobin Bart hydrops fetalis (Hb Bart) syndrome and hemoglobin H (HbH) disease. It is highly prevalent in South-East Asia or Mediterranean countries. The most common deletion reported in alpha thalassemia in Pakistani population was -α3.7 with a frequency of 8.3%, and the rare forms were -α4.2 (0.2%) and αααanti3.7 (0.9%). In our study, diagnosis of severe anemia cases without any α and β mutations or deletions were made by using extended alpha thalassemia deletions panel. The main objective of this study was to determine the prevalence and to study the spectra of alpha thalassemia gene deletions in beta thalassemia patients with the use of an extended panel including --SEA , --FIL , --MED , --20.5 , --THAI in addition to -α3.7 , -α4.2 & -αααanti3.7 .

METHODS: The samples were collected in ethylenediaminetetraacetic acid (EDTA) vacutainers. A total of 156 samples were analyzed for alpha thalassemia mutations. This cohort included 121 samples of beta thalassemia major, nine samples of beta thalassemia minor and 26 without any evidence of beta thalassemia mutations. DNA was extracted with Qiagen extraction kit. The primers for determination of different subsets of alpha thalassemia deletions were included. PCR amplification was performed and result interpreted on agarose gel.

RESULTS: Co-inheritance of alpha thalassemia (-α3.7, -α4.2 ) with homozygous beta thalassemia was detected in 30% cases of studied cohort (37 out of 121). The most common found was -α3.7 deletion (35/37) as single/double deletions or in combination with -αααanti3.7 . In undiagnosed cases screened for beta thalassemia major, we found Mediterranean (-αMED ) deletion at specifically 875 bp on agarose gel. This is distinctive finding in case of detecting -αMED instead of any other deletion from Pakistan.

CONCLUSION: Alpha thalassemia deletions (-α3.7, -α4.2 ) are the common co-inherited deletions found in beta thalassemia major patients. On the basis of results, we propose an extended alpha thalassemia genetic mutation panel should be used for screening of children presenting with anemia with suspicion of haemoglobinopathy.