Disease Due to Chromosomal Abnormalities (Abnormal Number)

Human Health and Diseases of Class 12

Disease due to chromosomal abnormalities (abnormal number)

Mainly due to non disjunction of chromosomes during gametogenesis.

1.Down’s Syndrome (or Mongolism)

Due to extra number of autosome (2n + 1) i.e. 21st chromosome:

Mongoloid features with broad head, round face, open mouth, thick tongue.

Slanting eyes and mentally retarded.

2.Patau’s Syndrome:

Due to extra number of autosome i.e. 13th chromosome (2n +1)

Characterised by mental deficiency, deafness, cleft lip, cleft palate, polydactyly, etc.

3.Edward’s Syndrome:

Due to extra number of autosome (2n +1) i.e., 18th chromosome.

Many congenital malformations occur, like, small mouth and nose, small mandible and ear, mental deficiency, large horse-shoe kidney and short sternum. 90% die in six months age.

4.Klinfelter’s Syndrome (XXY - individual)

Male with underdeveloped testis, enlarged mammary gland.

Retarded mental ability and criminal bent of mind.

5.Turner’s Syndrome (XO individual)

X from sperm but no sex chromosome from ovum (2n–1), such individuals are sterile female.

YO individuals are not viable.

Abnormalities related to the defects of arms of autosomes.

6.Cri-du-chat or Cat-cry syndrome

Due to shortening in the short arm of chromosome number 5.

Microcephaly (small head), broad face, saddle nose, mental retardation and stunted growth, less I.Q.

Death occurs in early childhood.

Baby crys like mewing of cat

7.Philadelphia syndrome

Due to defect in the long arm of chromosome number 22.

Chronic granulocytic leukemia occurs.

IDS (Acquired Immunodeficiency Syndrome)

Two persons independently discovered Immunodeficiency Virus (HIV): Lue Montagnier (1984), a French Robert Gallo (1984) an American,

who named it as HCLV-III (human cell leukemia virus).

There are 2 types of HIV — HIV-I and HIV-II, HIV-I is most common; SIV in monkey is similar to HIV-II.

HIV structure and pathogenesis

A retrovirus, HIV consists core of two single stranded RNAwith reverse transcriptaseenzyme surrounded by a protein capsidof two layers, inner P24and outer P17protein coats with incorporated glycoproteins (GP120 and GP41)

Disease Due to Chromosomal Abnormalities (Abnormal Number)

Fig.A schematic diagram of the Human Immunodeficiency Virus(HIV)

Retrovirus uses reverse transcriptaseto synthesize DNA from RNA; which is incorporated into the host’s DNA.

GP120 combines with CD4 receptor on T-helpercells which the virus affects.

The normal T-cell count is 500/mm3, but falls below 200/mm3in HIV infection.

HIV thus causes immunogenic imbalance.

Immune system collapse and patient die due to uncontrolled secondary infections.

Symptoms :swollen lymph nodes, prolonged mild fever, diarrhoea.

Advance stage is characterised by one of 24 specific opportunistic infections; common are - Pneumocystis cariniipneumonia(PCP) and

Kaposi’s sarcoma (KS), type of skin cancer.


HIV is a fragile virus, does not survive for long outside body, dies during dishwashing, cloth washing. If exposed to 135°F (56°C) temperature

for 90 minutes the virus dies.

Disease Due to Chromosomal Abnormalities (Abnormal Number)

Fig.High-risk Activities of AIDS Transmission

Sexual contact and infected blood contact are common means of transmission.

From infected mother to foetus through placenta and through breast feeding.

Homosexual relationship and sharing of needles for drug abuse are high risk groups.

AIDS Related Complex

Milder form of AIDS; symptoms include swollen lymph nodes, fever, night sweats and weight loss.


Once infected, detectable antibody titre occurs within 6-8 weeks; which can be detected by ELISAand confirmed by western blot test.

The oraquick diagnostic deviceused to detect AIDS in less than 20 minutes; uses less than a drop of blood and accuracy rate is 99.6%.


Commonly used drugs are AZT (Azidothymidine)or Retrovir, DDI (Dideoxyinosine), DDC (Dideoxycytidine)and D4T (Stavudine).All

drugs are nucleotide analogues, block the conversion of retroviral RNA to gene.

Other drugs are protease inhibitorlike Saquinavir (Invirase), Indinavirand Ritonavir.

World AIDS Dayis on 1st December

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