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His seminal findings rewrote many of the existing notions and thoughts about the infectious disease susceptibility and the peopling of India, which are revolutionary and not yet very much known in the medical circle and Indian society.
The discovery of the genome predisposing for Leprosy published in Nature Genetics in 2001 and its confirmation by another paper again in Nature Genetics in 2003 by Canadian and French scientists in Vietnam changed the general view of the world that microbes causes disease: but our studies proved that the host genetics is more important than the infection by Mycobacterium leprae per se: recall the ‘seed and the soil’ policy of Rao in his Text Book of Tuberculosis: a lotus cannot be grown in a desert and a cactus cannot be grown in a pond. Similar concepts and evidences have also been provided in tuberculosis susceptibility in the form of HLA DR2 and KIR and other gene polymorphisms.
An accidental discovery in 2001 was the ‘First migration of Man from Africa to Australia through the coasts of India’, in the form of Virumandi: This led to the documentary 'Journey of Man' 2002 by National Geogrpahic, the story told by Spencer Wells. The senior author of our paper Sir Walter Bodmer when said that we, all were descendant from Africa, everybody had to believe and Spencer could convince National Geographic, IBM and Tedd Waitt Family foundation to bequeath 20 million US$ for a public project called ‘The Genogrpahic’. Prof. Pitchappan had the previledge of organizing the Indian chapter of The Genogrpahic, sampled ~12000 men from all over India and studied their NRY and mtDNA polymorphisms.
Studies over the three decades on the HLA distribution in Indian populations and their association on HIV susceptibility, psoriasis, leprosy, tuberculosis etc., in India, all pointed towards the Population diversity and the resultant differential infectious disease susceptibility. Many seminal papers on HLA, KIR, skin color, whole genome scans all propose India, particularly southern India as a focal point of the origin of these diversity.
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