Write a brief note on each.

a. Down syndrome

b. Monogenic disorders

c. Sickle cell anaemia: symptoms and treatment.

a. Down’s Syndrome: Down's syndrome is caused due to the presence of an additional copy of chromosome 21 (Trisomy of 21). It was the first discovered and described chromosomal disorder in humans. The total number of chromosomes in people affected with Down's syndrome becomes 47. Affected individual has short stature, small, round head, furrowed tongue, partially opened mouth, palm crease, congenital heart disease and mental retardation.

b. Monogenic disorders: Monogenic disorders are genetic disorders which are caused by a mutation in a single gene. This mutation may be present on one or both the chromosomes. Some of the examples of monogenic disorders are sickle cell anemia, cystic fibrosis, polycystic kidney etc.

c. Sickle cell anaemia: Sickle-cell anaemia is an autosome-linked recessive trait exhibiting change in shape of the red blood cells from biconcave disk to sickle shape under low oxygen tension. It is a result of replacement of GAG by GUG leading to the substitution of Glu by Val at sixth position of beta globin chain of haemoglobin. It is characterised by low haemoglobin count and other symptoms of anaemia such as fatigue and irritability, swelling on hands and legs, pain in joints, constant low grade fever etc.
There is no particular treatment for sickle cell anemia, the treatments which are available provide symptomatic relief from the symptoms associated with this disorder.