Autosomal recessive disorder - Cystis fibrosis Sickle cell anaemia .Tay sachs disease.

• In autosomal recessive inheritance, Two copies of a defective gene are present in an affected individual.  Each copy comes  from each parent.

• Autosomal recessive inheritance means that the gene is located on one of the autosomes or allosome or non sex chromosome. This means that males and females are equally affected. 

• Two copies of the defective gene are necessary to be present in the affected individual. one inherited from the mother, and one from the father. These disorder is caused by the Mutations. 

Cystic fibrosis 

• Cystic fibrosis is one of the most common disorders in the European population.  The characteristics of this genetic disorder are as -  

• Body secretes abnormal body fluids and  unusual sweat and a thick mucus. These unusual  fluids prevent  the body from properly cleaning the lungs. 

• The mucus  disturbs the function of vital organs and leads to chronic infections. 

• Cystic fibrosis also affects pancreas and causes decreased absorption of essential nutrients.

• Eventually death occurs from respiratory failure. Most of the  people may have sinusitis, or infertility.

Read more about the Autosomal dominant disease

Sickle cell anemia 

• Sickle cell anemia is the result of point mutation.

• It is transmitted to the offspring when both the parent are carrier for the gene.

• Sickle cell anemia is controlled by a single pair of allele, HbA and HbS. 

• The homozygous individuals for Hbs and Hbs is affected from sickle cell anemia.

• The Heterozygous individuals  for HbA and HbS  are carrier of the disease

• Sickle cell disease affects  the red blood cells and   their ability to carry oxygen. Normal shapes of red blood cells are smooth, round, and biconcave so they can move through the vessels in our bodies.

• But in Sickle cell anaemia, Red blood cells become stiff and sticky  and their shape is changed from biconcave to sickle shaped. These sickle shaped red blood  cells are clumped  together and cannot easily move through the blood vessels.

• As a result there is a blockage in blood vessels  and stops the movement of blood. This blockage is painful.

• Sickle shaped red blood lost its life  in 15 days, whereas normal red blood  cells can live up to 120 days.

• Sickle shaped red blood  cells also affect  the spleen because of their shape and stiffness.

• Due to the irregular red blood shape of RBC a person with sickle cell anaemia  is chronically anemic.

• After repeated blockages,  the size of the spleen is reduced  and does not work properly.

• Treatment includes prompt emergency care for fevers and infections, appropriate vaccinations, penicillin, and management of anemia.

• Sickle cell anaemia is caused by the substitution of amino acids glutamic acid by valine at 6th position at Beta chain of hemoglobin by the point mutation.

• The substitution of amino acid in the globin protein results due to the single base substitution at the sixth codon of the beta globin gene from GAG to GUG. 

Read more about X linked dominant disease

Tay Sachs disease

• Tay Sachs disease is a fatal disorder in infant  that causes a degeneration of the central nervous system.

• It is caused by the absence of an enzyme called hexosaminidase A. Without this enzyme, a fatty substance is accumulated near or  on the nerve cells in the body or the brain.

• The process begins early in pregnancy when the baby is developing. There is no remarkable treatment of this disease so far.

• Dr. Tay and Dr. Sachs was who described this genetic disorder so it is called  Tay Sachs disease.

Thalassemia

• This is also an autosome-linked recessive blood disease transmitted from parents to the offspring when both the partners are unaffected carrier for the gene (or heterozygous).

• The defect could be due to either mutation or deletion which ultimately results in reduced rate of synthesis of one of the globin chains that make up haemoglobin . This causes the formation of abnormal haemoglobin molecules resulting into anaemia which is characteristic of the disease.

Read more about the X linked recessive dosorder

• Thalassemia can be classified according to which chain of the haemoglobin molecule is affected. In alpha Thalassemia, production of alpha globin chain is affected while in Thalassernia, production of globin chain is affected

• Alpha Thalassemia is controlled by two closely linked genes HBA l and HBA2 on chromosome 16 of each parent and it is occur due to mutation .

• While Beta Thalassemla is Controlled by a single gene H BB on chromosome 11of each parent and occurs due to mutation of one or both the genes.

• Thalassemia differs from sickle-cell anaemia in that the thalassemia is a quantitative problem of synthesising too few globin molecules while the sickle cell anemia is a qualitative problem of synthesising an incorrectly functioning globin.

Phenylketonuria 

• It is an inborn error of protein metabolism. Due to protein metabolism body produced phenylalanine amino acid that should be converted into tyrosine .

• A gene for enzyme phenyl alanine hydroxylase that is responsible for the conversation of phenylalanine into tyrosine , is eliminated.

• As a result , phenyl alanine and their derivative phenyl pyruvic acid are accumulated in body and it causes Mental retardation and loss of hair and skin pigmentation.

• These derivative are excreted into urine due to its poor absorption by kidney.

• Phenylketonuria is an example of pleiotropy in which one gene affect more than one phenotype expression. This disorder causes Mental retardation as well as loss of skin  and hair pigmentation.