Metabolic diseases are detected by the defect in the specific enzyme in red blood cells. One among them is sex linked Glucose-6-Phosphate Dehydrogenase(G6PD). It is one of the most studied of all red cell enzyme, with the importance of its location in the beginning of the HMP pathway and the precursor of nuclic acids and of all nucleotide co-enzymes.Deficiency of which causes complications in fava beans eating individuals and in those taking certain kinds of anti-malarial drugs. Owing to a variety of bio-synthetic and detoxification reactions associated with G6PD, this book dealt with variation in the G6PD deficiency in two endogamous populations of India, namely, Jats and Brahmins.