Date：2022-03-02

What are Genetic Disorders?

Genetic disorders refer to the conditions caused by a change in the genome. It can be caused by a single-gene factor (e.g. Huntington’s disease) or a complex disorder caused by multiple genes and environmental factors (e.g. cancer). Some genetic disorders are chromosomal disorders that involve the changes in the number or structure of chromosomes (e.g. Down syndrome).

Basic Patterns of Inheritance for single-gene disorders

The 23 pairs of chromosomes contain various kinds of genes. 22 pairs of them are called autosomes found in both males and females. And there is one pair of sex chromosomes (XX for females and XY for males) to determine the sex of an individual. Some genetic disorders are dominant, and some are recessive, depending on the inheritance pattern. There are several basic inheritance patterns for single-gene disorders.

Autosomal dominant inheritance

Just one copy of the gene from either one of the parents is sufficient to cause an autosomal dominant disorder. In some cases, the conditions are caused by a new variant of an individual without a family history of the disease. Huntington’s disease, tuberous sclerosis, and neurofibromatosis are examples of autosomal dominant disorders.

Autosomal recessive inheritance

In autosomal recessive disorders, the parents of an affected individual both carry one copy of the mutated gene. They usually are the disease carriers without showing any disease phenotypes. Cystic fibrosis and Wilson’s disease are examples of autosomal recessive disorders.

X-linked dominant inheritance

The genes affecting X-linked dominant disorders are located on the X chromosomes. Both females and males can be manifest the diseases when they have only one copy of the gene passed from either of the parents. Since females have two X chromosomes and males only have one X chromosome, X-linked dominant disorders more frequently affect females than males. Rett syndrome is one of the examples of X-linked dominant disease.

X-linked recessive inheritance

The genes affecting X-linked recessive disorders are also located on the X chromosomes. X-linked recessive inheritances are more frequently affect males than females. It is because there is only one X chromosome in males. Only one copy of the mutated gene is sufficient to cause the disease in males. And it required two copies with mutated genes from both parents to affect a female individual. Duchenne muscular dystrophy and haemophilia are examples of X-linked recessive disorders.