University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

86

Pages:

2
Author:

Mariam A. A.

Transmission Patterns of Single-Gene Disorders Single-gene disorders are caused by mutations in a single gene and are often inherited in predictable patterns within families. Understanding these transmission patterns is crucial for genetic counseling, diagnosis, and potential treatment strategies. 1. Autosomal Dominant Inheritance 2. Autosomal dominant disorders occur when a person inherits one mutated copy of the gene from either parent. This mutated allele is dominant over the normal allele, meaning a person with the mutation will express the disorder, regardless of whether the other allele is normal or mutated. Key points include: • • • Vertical Transmission: Each affected individual usually has an affected parent, and approximately 50% of their offspring will inherit the disorder. Variable Expressivity: Symptoms can vary widely among affected individuals, even within the same family, due to genetic modifiers or environmental factors. Penetrance: Refers to the likelihood that a person with a mutation will actually show symptoms of the disorder. Examples include Huntington's disease and Marfan syndrome. 2. Autosomal Recessive Inheritance Autosomal recessive disorders require inheritance of two copies of the mutated gene (one from each parent) to manifest the disorder. Carriers (individuals with one mutated copy and one normal copy) typically do not show symptoms but can pass the mutation to their children. Key points include: • • • Horizontal Transmission: Often skips generations because carriers do not exhibit symptoms. Consanguinity: Increased risk in populations with high rates of consanguineous marriage due to the higher probability of both parents carrying the same recessive allele. New Mutations: Occasionally, recessive disorders can occur due to new mutations in families with no previous history. Examples include cystic fibrosis and sickle cell disease. 3. X-Linked Inheritance X-linked disorders are caused by mutations in genes located on the X chromosome. Males are more frequently affected because they have only one X chromosome (XY), whereas females have two (XX). Key points include: • • • X-Linked Recessive: Typically affects males, who inherit the mutated gene from their carrier mothers. Females are usually carriers unless they inherit two mutated alleles. X-Linked Dominant: Both males and females can be affected, with different patterns of inheritance compared to recessive X-linked disorders. Skewed Inactivation: In females, X chromosome inactivation can lead to varying degrees of expression of X-linked disorders.