How are cystic fibrosis and Huntington’s disease inherited?

Sourav PanNovember 8, 2024

Answered

Cystic fibrosis and Huntington’s disease are inherited through distinct genetic mechanisms, reflecting different patterns of inheritance. Here’s a detailed overview of how each condition is passed on from parents to offspring.

Cystic Fibrosis

1. Inheritance Pattern:
   • Cystic fibrosis (CF) is inherited in an autosomal recessive manner. This means that an individual must inherit two copies of the mutated gene (one from each parent) to develop the disease. If a person has only one mutated copy (making them a carrier), they typically do not show symptoms of the disease .
2. Genetic Basis:
   • The disease is caused by mutations in the CFTR gene (cystic fibrosis transmembrane conductance regulator), located on chromosome 7. Over 1,800 mutations have been identified, with the most common being the ΔF508 mutation, which leads to dysfunctional CFTR protein responsible for regulating salt and water transport in cells .
3. Risk of Inheritance:
   • When both parents are carriers (each having one normal allele and one mutated allele), there is a:
     • 25% chance that their child will inherit two mutated alleles and have cystic fibrosis (genotype ff).
     • 50% chance that their child will be a carrier (genotype Ff) but not have the disease.
     • 25% chance that their child will inherit two normal alleles (genotype FF) and not be a carrier or affected .
4. Population Considerations:
   • CF is more prevalent among certain ethnic groups, particularly those of Northern European descent, where about 1 in 25 people are carriers of the CF gene .

Huntington’s Disease

1. Inheritance Pattern:
   • Huntington’s disease (HD) is inherited in an autosomal dominant manner. This means that only one copy of the mutated gene is sufficient to cause the disorder. An affected individual has a 50% chance of passing the mutated allele to each child .
2. Genetic Basis:
   • The disease is caused by mutations in the HTT gene, located on chromosome 4, characterized by an expanded CAG trinucleotide repeat. Individuals with 40 or more repeats typically develop symptoms, while those with fewer repeats may not exhibit symptoms but can still pass on the mutation .
3. Risk of Inheritance:
   • If one parent has Huntington’s disease, each child has a:
     • 50% chance of inheriting the mutated gene and developing HD.
     • 50% chance of inheriting the normal gene and not developing the disorder.
4. Generational Impact:
   • Huntington’s disease often appears in successive generations due to its dominant inheritance pattern, leading to vertical transmission within families . Additionally, there is a phenomenon known as “anticipation,” where the number of CAG repeats can increase in successive generations, potentially leading to earlier onset and more severe symptoms in descendants .