In a new finding, a mutation in TAP1 gene has been associated with susceptibility to leprosy in Indians.

TAP1 gene is one of the several genes that regulate the immune response and its variations were earlier implicated in tuberculosis and auto-immune diseases.

While many people get exposed to Mycobacterium leprae , not all develop symptoms for leprosy. Since variations in some genes were reported to increase the risk, researchers from India and Germany looked at the role of TAP1 (Transporter associated with antigen processing) gene for susceptibility to leprosy.

As many as 222 leprosy patients, who were carriers of few and multiple bacteria of the same strain were enrolled for the study. The DNA data bank from CCMB was utilised for another group of 223 ethnically matched control individuals from the same socio-economic and geographical region.

In the paper published recently in Human Immunology , the authors of the study noted: “Our results provide genetic evidence that polymorphism in the TAP1 gene influences susceptibility to leprosy in Indian population.” According to a scientist involved in the study, TAP1 gene mutations were found to be associated in certain other populations earlier and this was the first time that its variations were linked to Indian leprosy patients.

He said that screening would help in cases with family history of leprosy. Precautionary measures could be taken if anybody was found with this mutation.

Explaining how the mutation affects immunity, the lead author of the study, Dr. Vijaya Lakshmi Valluri, Group Leader, Immunology & Molecular Biology Division, Blue Peter Public Health and Research Centre, Hyderabad, pointed out that the body’s immune system responds whenever a foreign protein, bacteria or virus enters the system.

Mode of action

She said M. leprae were intracellular bacteria and the T-cells get activated to eliminate the cells harbouring these bacteria. TAP1 was involved in the binding of bacterial peptide on to MHC (major histocompatibility complex) molecules, which then move to the cell surface and induce T-cell activation. However, if the binding of the bacterial peptide was not proper, the immunity gets compromised.

She said a wide range of clinical manifestations were normally seen in leprosy, depending on the immune response of the patient to the bacteria. A milder form of the disease, tuberculoid leprosy, was paucibacillary (few bacteria) and characterised by less number of skin lesions as compared with multibacillary form, which normally is more severe. Both the types cause permanent damage to peripheral nerves.

Five institutions — Lepra Society's Blue Peter Public Health and Research Centre, CSIR-Centre for Cellular and Molecular Biology (both in Hyderabad), Institute of Tropical Medicine, University of Tubingen, Germany, Department of Zoology, School of Life Sciences, Bharathiar University, Coimbatore and National Institute of Pathology, Delhi were involved in the study.