Genetic epidemiology, classification of Genetic Disorder, factor causing genetic abnormalities, difference between congenital and teratogenic abnormalities and prevention of genetic diseases

Genetic epidemiology, classification of Genetic Disorder, factor causing genetic abnormalities, difference between congenital and teratogenic abnormalities and prevention of genetic diseases

1. Genetic Epidemiology Edenburgh International College Mohan Bastola BPH 5 th S em

2. Concept: Gene, are the unit of heredity. They contain the hereditary information encoded in their chemical structure for transmission from generation to generation. unit of hereditary information that occupies a fixed position (locus) on a chromosome. Genes achieve their effects by directing the synthesis of proteins. Genetics  is the study of genes, heredity, and genetic variation in living organisms ( Hartl D, Jones E (2005). Each human cell nucleus contains 46 chromosomes, that carry hereditary information and genetics is the study of how this information is transmitted from parents to offspring.

3. Contd.. Genetic epidemiology was defined by Newton Morton as "a science which deals with the etiology, distribution, and control of disease in groups of relatives and with inherited causes of disease in populations“ (Morton, N. E.) (1982). Genetic epidemiology is defined as the study of the distribution of and risk factors for diseases and genetic and environmental causes of familial resemblance.

4. Classification of genetic disorder Chromosomal abnormalities Unifactorial (single gene or Mendelian) diseases Multifactorial disorder

5. Chromosomal disorder A chromosomal disorder, anomaly, aberration, or mutation is a missing, extra, or irregular portion of chromosomal DNA. It can be from a typical number of chromosomes or a structural abnormality in one or more chromosomes . They are of 2 types: Relating to sex chromosomes Relating to autosomes

6. Relating to sex chromosomes Klinefelter’s syndrome: The person suffering from this syndrome are abnormal males having two or more X chromosomes in addition to one Y chromosome (XXY, XXXY). It only affects males. They have non-functional testes. Growth of hair on face, axillae and pubes is scanty .

7. 2.XYY syndrome: The male with an extra Y chromosome attached. They have anti-social, aggressive and criminal behavior. They appear to be exceptional height (usually 6 ft and over).

8. 3. T urner’s syndrome Turner syndrome is a chromosomal condition that affects development in females . The most common feature of Turner syndrome is short height, which becomes evident by about age 5 . An early loss of ovarian function (ovarian hypo function or premature ovarian failure) is also very common . They have 45 chromosome which constitute of XO instead of XX(O represents missing chromosome)

9. 4. Super females They are females with 3 to 5 X-chromosomes. They have underdeveloped external genitalia, uterus and vagina. Triple X syndrome, also known as trisomy X and 47,XXX, is characterized by the presence of an extra X chromosome in each cell of a female Relating to autosomes: Down syndrome  (DS or DNS), also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual disability, and characteristic facial features.

10. Unifactorial (single gene or Mendelian) diseases A single gene disease occurs due to a change in a gene that leads to loss or disturbed function of that gene . They are: Sickle cell anemia Thalassaemia Haemophilia Cystic fibrosis phenylketonuria

11. Thalassaemias it is a hereditary disorder characterized by the reduction in the synthesis of globin chain(alpha or beta). It causes reduced haemoglobin synthesis. Sickle cell anemia: An inherited, chronic disease in which the red blood cells, normally disc shaped, become sickle shaped. Mostly prevalent among blacks, especially in certain parts of Africa and tharus community in western part of Nepal.

12. Haemophilia It   is inherited genetic disorder in which the blood does not clot properly. Also known as royal disease. It mostly affects men.

13. Cystic fibrosis Is a genetic disease which affects respiratory and gastrointestinal tracks and sweat glands. The body produces thick and sticky mucus that can clog the lungs and obstruct the pancreas .  Cystic fibrosis (CF) can be life-threatening, and people with the condition tend to have a shorter-than-normal life span

14. Phenylketonuria(PKU) It is an autosomal recessive disorder resulting in the deficiency of liver enzyme phenylalanine hydroxylase which converts phenylaline to tyrosine. It results in decreased metabolism of the amino acid phenylalanine. Untreated , PKU can lead to intellectual disability, seizures, behavioral problems, and mental disorders. It may also result in a musty smell and lighter skin.

15. Multifactorial Genetic Disorder Multifactorial inheritance is also called complex or polygenic inheritance. Multifactorial inheritance disorders are caused by a combination of environmental factors and mutations in multiple genes. For example, different genes that influence breast cancer susceptibility have been found on chromosomes 6, 11, 13, 14, 15, 17, and 22. Some common chronic diseases are multifactorial disorders .

16. Factor causing genetic abnormalities: A genetic disorder is a disease caused in whole or in part by a change in the DNA sequence away from the normal sequence . Changes in the genes causes mutation, alter the structure function of the gene product which give rise to diseases. Combination of gene mutations and environmental factors D amage to chromosomes. Translocation Inversion.

17. Difference between congenital abnormalities and teratogenic abnormalities A congenital malformation is an anatomical or structural abnormality present at birth. It can be caused by genetic factors or environmental insults or a combination of the two that occur during prenatal development. Most of them demonstrate multifactorial inheritance with a threshold effect and are determined by a combination of genetic and environmental factors. Some birth defects are life-threatening, in which case a baby may only live for a few months.

18. Contd.. Teratogens are the substances that alter an environment within womb / fetus to cause the birth defects, e.g., alcohol, nicotine/smoke, certain medicines, numerous industrial chemicals, etc. during pregnancy. The combined consequences of consuming a harmful substance, such as the alcohol, on a developing fetus may manifest itself as growth deficiency and mental retardation.

19. Prevention of genetic diseases: avoiding harmful environmental factors which increase the mutation frequency; screening all newborn infants for diseases when early treatment can prevent the occurrence of physical and/or mental handicaps ; early detection of couples at risk, followed by genetic counselling and preventative measures in case of pregnancy .

20. Reference: K.PARK (25 TH edition) https://www.britannica.com/science/gene https://www.genome.gov/For-Patients-and-Families/Genetic-Disorders https://www.medicinenet.com/genetic_disease/article.htm https:// www.yourgenome.org/facts/what-are-single-gene-disorders https:// www.yourgenome.org/facts/what-is-a-chromosome-disorder.

21. thank You.