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Introduction: Before the recent progress in molecular genetics (1980), medical genetics were limited to observation of sex chromatin in different genetic disorders. Human cell nuclei contain 46 chromosomes: In male 44 + X and Y In female 44 + X and X In Mongols, total number of chromosomes is 47. In Klinefelter syndrome the number is 47 (44 + XXY) In Turner syndrome the number is 45 (44 + XO). This is due to failure of separation of X and Y during meiosis, so that spermatozoa contain XY or O. Fertilization of normal ova containing X results in XXY (Klinefelter syndrome) or XO (Turner syndrome). Intersex: "Intersex" is a general term used for a variety of conditions in which a person is born with discrepancy between the external genitals and the internal genitals (the testes and ovaries). Cause for deviation from normal sexual orientation: Social ; psychological ; anatomical, endocrine ; chromosomal. Example: Homosexual, adrenal virilism, true hermaphroditism etc.
Progress in molecular genetics has revolutionized the study of medicine. Recent progress has resulted from the advances in molecular biology, involving recombinant DNA technology. Application of DNA technology on medicine: Example: 1. Molecular basis of diseases: (i) Inborn errors of metabolism. Example: Phenylketonuria ; disorder of Hemoglobin synthesis. (ii) Cystic fibrosis (Cystic Fibrosis of the Pancreas) (iii) Neurofibroma (iv) Duchenne muscular dystrophy (v) Huntington's disease (vi) Diseases involving both genetic and acquired factors. Example: viral hepatitis, diabetes mellitus , tumours. 2. Production of human biologically active agents : Unlimited quantities are produced in tissue and bacterial culture for therapeutic application. Example: i) Tissue plasminogen activator (tPA) for treatment of thrombotic states. ii) Growth hormone for the treatment of deficiency states. iii) Erythropoietin in anemia of renal origin. iv) Myeloid growth and differentiation factors (GM-CSF, G-CSF) in poor marrow function. 3. Gene therapy: For the treatment of genetic diseases. Example: lack of the enzyme adenosine diaminase (ADA). 4. Diagnosis of disease: Molecular probes are very useful in the diagnosis of both genetic and non-genetic (Eg: Infections) diseases. Diagnosis of Genetic Disease
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