Genetic Diseases

1. Sickle cell anaemia : (Genetic Diseases)

Sickle cell anaemia is a genetic syndrome caused by an autosomal
mutant allele Hbs. In homozygous condition (Hbs Hbs), it causes the
production of an abnormal haemoglobin called haemoglobin S. The
normal haemolobin is designated as HbA (HbAHbA). Sickle cell persons with
the genotype HbsHbs suffer from a fatal haemolytic anaemia. The
patient dies due to damaged heart, kidney, spleen and brain as a result of
clogged blood vessels or vascular obstruction. Persons with heterozygous
genotype HbA Hbs are said to be carriers and they survive.

2. Thalassemia : (Genetic Diseases)

Thalassemia is an erythroblastic anaemia due to homozygous
recessive gene expression in children. Two types of this disease viz.,
thalassemia major and thalassemia minor exist. The former is the severe form
while the latter is its milder form. The homozygotes suffer from
severe thalassemia while all heterozygotes suffer from milder thalassemia.
The clinical manifestations of thalassemia include I) decrease in the bone
marrow activity, ii) peripheral haemolysis, iii) splenomegaly (enlarged spleen)
and hepatomegaly, (enlarged liver) etc. The thalassemic children die at the
age of seventeen.

3. Agammaglobulinemia : (Genetic Diseases)

Agammaglobulinaemia is a recessive gene disease, wherein
r-globulin synthesis fails to occur. In this disease, the patient shows a great
deficiency or total absence of plasma cells and unusual lymph nodes with
fewer lymphocytes than normal. The failure of antibody synthesis in this
disease, makes the subjects more prone to viral and bacterial infections
especially of the chest .This disease mostly affects boys.

4. Albinism : Genetic Diseases

It is an inherited disorder of melanin metabolism
characterized by the absence of melanin in the skin, hairs and eyes. The
clinical characteristics of this disease are the milk-white coloured skin and
marked photophobia. Albinism is an inborn error metabolic disease, In this, the genes by undergoing mutation do not produce particular enzymes, which
take part in the metabolic pathways. The metabolism of one amino acid
phenylalanine proceeds in chains of enzyme-mediated reactions. The change
or absence of enzyme due to defective genes, results in physiological
abnormalities. In albinism, complete lack of melanin pigment (a dark brown
pigment) causes the albino to suffer. The incidence of albinism in human has
been reported to be from 1:5000 to 1:25000. The albinism may be generalized
albinism, localized albinism of the eye (ocular albinism) or partial albinism
(skin and hair). The recessive genes ‘aa’ do not produce the tyrosinase
enzyme, which converts DOPA (3,4 – dihydroxy phenyl alanine) into melanin
in the melanocytes.

5. Huntington’s chorea : Genetic Diseases

This is a fatal disease caused by an autosomal dominant gene in human.
The onset of the disease is between 35 and 40 years of age. It is
characterized by uncontrolled jerking of the body due to involuntary
twitching of voluntary muscles. It leads to progressive degeneration of the
central nervous system accompanied by gradual mental and physical
deterioration. Huntington’s disease was the first completely dominant
human genetic disease to come to light. The affected gene is located on chromosome 4. Other characteristics of this disease are deterioration of intellectual faculty, depression, occasional hallucination and delusions and other psychological problems. This disease is incurable.

6. Severe Combined Immunodeficiency (SCID) : Genetic Diseases

This is an extremely rare inherited disease affecting children. The gene
for the disease called ADA (Adenine deaminase) is located on
chromosome 20. The children suffering from the syndrome completely lack
the immune defense mechanism against infection due to rapid death of all
white blood cells. SCID is also called Bubble Boy Syndrome. The child is
kept in a sterile bubble. Unless given bone marrow transplant, the child’s life
span is short lived.