As stated in HGP or the Human Genome Project, diseases develop influenced by genetic as well as environmental factors. Hereditary diseases, also called genetic disorders, are diseases inherited from people in the family. These diseases are primarily classified into four categories; mitochondrial, single gene, chromosomal and multifactorial.
Types of Hereditary Diseases Hereditary diseases are generally classified according to the Mendelian disease category and the most common types of hereditary disease are:
- Dominant: Here the disease symptoms manifest in case one allele gets defected.
- Recessive: In this type, both alleles should get defected for manifestation of the disease.
- Sex Linked: Here the allele exists on chromosome X only, thereby making males highly vulnerable to any particular disease.
Common Hereditary Diseases Some of the most common hereditary diseases include Marfan syndrome, Tay Sachs disease and sickle cell anemia. 
Marfan syndrome: It is a genetic disorder in which connective tissues are affected and about one in every 5,000 people gets affected by this syndrome.
The effects of this syndrome are that the body becomes lean and tall but torso is short, fingers are thin and abnormalities exist in the chest wall. Abnormalities are also seen in blood vessels, joints and eyes but this syndrome does not affect intelligence of a person.
Sickle Cell Anemia: It is a complicated blood disorder where sickle shaped red blood cells are produced by the body. Normally these cells are disc shaped which helps them to pass through blood vessels easily.
Haemoglobin in red blood cells is responsible for carrying oxygen to cells in the body from the lungs and abnormalities in haemoglobin result in red blood cells to become sickling. The improper circulation due to blockage of blood vessels results in pain and organ damage.
Tay Sachs Disease: It is called as progressive neurological genetic disorder or PNGO. The disease manifest in 3 forms; Late Onset, Classic Infantile and Juvenile.
The primary reason for this disease is absence of Hexosaminidase A enzyme in body. Absence of this enzyme leads to accumulation of lipid GM2 ganglioside in nerve cells in the brain and progressive accumulation results in damage of the nerve cells. In infants, the disease begins during pregnancy itself and symptoms only appear several months after child’s birth. As the child reaches age or 3 or 4, the nervous system is so damaged that the child cannot be saved.
Summary:
There are many hereditary diseases which can be life threatening and it is important to always consult a doctor and follow proper medication if any such problem is diagnosed.
