Monogenic diseases, also known as Mendelian disorders, are genetic disorders caused by mutations in a single gene. These disorders are typically inherited in a simple Mendelian fashion, following patterns of inheritance determined by the specific gene involved. Genes can be located either on one of the numbered (1-22) chromosomes and are called autosomal, on the sex X chromosome (Χ-linked), or the Y chromosome. Monogenic diseases can be classified into several categories based on the inheritance pattern:
Autosomal Dominant Disorders
- In these disorders, a mutation in one copy of the gene (allele) is sufficient to cause the disease.
- Affected individuals typically have an affected parent, and there is a 50% chance of passing the mutation to each offspring.
Autosomal Recessive Disorders
- In recessive disorders, an individual must inherit two mutated copies of the gene (one from each parent) to express the disease.
- Carriers with one regular and one mutated copy are typically unaffected trait carriers.
X-linked Dominant Disorders
- These disorders are caused by mutations in genes located on the X chromosome.
- In females, one copy of the mutated gene is enough to express the disorder, while males, having only one X chromosome, are more severely affected.
X-linked Recessive Disorders
- In X-linked recessive disorders, males are more commonly affected because they have only one X chromosome.
- Females are typically carriers, having a second X chromosome that may carry a standard gene copy.
Y-linked Disorders
- Mutations in genes on the Y chromosome cause Y-linked disorders.
- Since the Y chromosome is passed from father to son, Y-linked disorders are typically limited to males.
Monogenic diseases often exhibit predictable inheritance patterns, and identifying the specific gene involved can provide valuable information for diagnosis, prognosis, and genetic counseling. Advances in genetic testing and molecular biology have facilitated the identification of causative mutations, allowing for early detection and, in some cases, the development of targeted therapies for these disorders. Understanding the genetic basis of monogenic diseases is crucial for clinical management and potential treatment research.
