© Kamla-Raj 2008 Int J Hum Genet, 8(4): 357-360 (2008) Alpha Thalassaemia: Experience of Referral Cases in Kolkata, India Tapash Rudra, Sila Chakrabarti and Bani Sengupta Thalassaemia Counselling Unit, Vivekananda Institute of Medical Sciences, 99 Sarat Bose Road, Kolkata 700 026, West Bengal, India KEYWORDS Haemoglobinopathies; Thalassaemia; anaemia, mutation ABSTRACT Haemoglobinopathies and different forms of thalassaemias including alpha thalassaemia has been found to be as high as 10% in Eastern India. The alpha globin disorders are less commonly reported because the diagnosis of alpha thalassaemia is usually missed unless in the severe homozygous form or as Hb Barts. But presence of alpha gene has been found in cases of unexplained anaemias and also in several suspected cases having ¦α mutations and other common haemoglobinopathies. Two of the common ¦ α mutations (-¦ α3.7, - ¦ α4.2) have been detected either in heterozygous or homozygous states in significant frequencies, so patients coming for Hb Electrophoresis and carrier detection should be also checked the alpha status through specific DNA studies. INTRODUCTION Thalassaemia describes a group of inherited disorders characterized by reduced or absent amounts of hemoglobin, the oxygen-carrying protein inside the red blood cells. There are two basic groups of Thalassaemia disorders: alpha Thalassaemia and beta Thalassaemia. These conditions cause varying degrees of anaemia, which can range from insignificant to life threatening. All types of Thalassaemias are considered quantitative diseases of hemoglobin, because the quantity of hemoglobin produced is reduced or absent. Usual adult hemoglobin is made up of three components: alpha globin, beta globin, and heme. Thalassaemias are classified according to the globin that is affected, hence the names alpha and beta Thalassaemia. Although both classes of Thalassaemia affect the same protein, the alpha and beta Thalassaemias are distinct diseases that affect the body in different ways. Most individuals have four normal copies of the alpha globin gene, two copies on each chromosome 16. These genes make the alpha globin component of normal adult hemoglobin, which is called hemoglobin A. Alpha globin is also a component of fetal hemoglobin and the other major adult hemoglobin called hemoglobin A2. Mutations of the alpha globin genes are usually deletions of the gene, resulting in absent production of alpha globin. Since there are four genes (instead of the usual two) to consider when looking at alpha globin gene inheritance, there are several alpha globin types that are possible. Absence of one alpha globin gene leads to a condition known as silent alpha Thalassaemia trait. This condition causes no health problems and can be detected only by special genetic testing. Alpha Thalassaemia trait occurs when two alpha globin genes are missing. This can occur in two ways. The genes may be deleted from the same chromosome, causing the ‘cis’ type of alpha Thalassaemia trait. Alternately, they may be deleted from different chromosomes, causing the ‘trans’ type of alpha Thalassaemia trait. In both instances, there are no associated health problems, although the trait status may be detected by more routine blood screening. Hemoglobin H disease results from the deletion of three alpha globin genes, so that there is only one functioning gene. Typically, this can occur when one parent carries the silent alpha Thalassaemia trait, and the other parent carries the ‘cis’ type of the alpha Thalassaemia trait. In this situation, there is a 25% chance for hemo- globin H disease in each of such a couple’s children. Hemoglobin H disease-like symptoms can also be a part of a unique condition called alpha Thalassaemia mental retardation syndrome (ALMRS). Alpha Thalassaemia mental retarda- tion syndrome can be caused by a deletion of a significant amount of chromosome 16, affecting Address for correspondence: Tapash Rudra Thalassaemia Counselling Unit, Vivekananda Institute of Medical Sciences, 99 Sarat Bose Road, Kolkata 700 026, west Bengal, India E-mail: tapashrudra@yahoo.co.in