Genetic disorders are caused by any abnormality within the genes. Genes are part of cell’s DNA that are carried in chromosomes. Genes are coded instructions for building proteins that determine structure and function of all the cells of the body. In other words, genes determine human characteristics such as color of the hair, height, weight and other. Personality and behavior of an individual also depend on genes. Apart from this, genes can transfer disorders and diseases from ancestors to descendants.
As it was mentioned above, genetic diseases and disorders result from abnormalities within genes or chromosomes. Mutation inside the genes, deletion of certain gene, chromosomal aberrations or other factors such as two recessive genes coming together or exposure to radiation can all cause genetic disorders. Inherited genetic disorders can be identified either immediately after person is born or when certain period of time goes by. Presently, there are over 4,000 genetic disorders though new disorders are constantly being discovered.
Types of Genetic Disorders
Genetic disorders include four types: single gene disorders, multifactorial problems, chromosomal abnormalities and mitochondrial mutations.
Single Gene Disorders
Single gene disorders, also called Mendelian or monogenic disorder, are caused by changes or mutations within the DNA sequence of a single gene. Single gene disorders have higher risk of inheritance. Single gene disorders include:
- Autosomal disorders - such as achondroplasia which is defective bone development that causes dwarfism. Autosomal disorders are caused by abnormal gene of one parent.
- Autosomal recessive disorders - such as sickle cell anemia and cystic fibrosis, which occur due to abnormal genes of both parents.
- X-linked disorders – include disorders such as hemophilia caused by single abnormal gene on the X chromosome.
- Y-linked disorders – mutation or abnormality is present only in Y chromosome. These disorders are passed from father to son.
Multifactorial or polygenic problems result from combination of environmental factors and mutations in multiple genes. These disorders include heart disease, high blood pressure, diabetes, obesity, asthma, autism, arthritis, cancer, ciliopathies, cleft palate, mental retardation and others.
These disorders occur due to abnormalities in number of chromosomes or structure of chromosomes and they are generally caused by problem with cell division. Chromosomal abnormalities include disorders such as Down syndrome, Turner syndrome, chromosomal sequence deletion, chromosomal sequence inversion and chromosomal translocation.
Mitochondrial mutations are always inherited from the female pattern because mitochondria are kept in the egg cells during fertilization. Mitochondrial mutations include Leber’s hereditary optic neuropathy, MERRF (type of epilepsy) and other disorders.