Huntington disease (HD) is an autosomal dominant progressive neurodegenerative d

Question

Huntington disease (HD) is an autosomal dominant progressive neurodegenerative disorder with a distinct phenotype. Typically, there are early symptoms of mild psychotic and behavioral symptoms which precede frank chorea by up to 10 years. Because Huntington's is rare, essentially everyone with the disease is a heterozygote. Mario's father has Huntington's, but there is no history of the disease on his mother's side.

1. What is the probability that Mario will develop Huntington's?

2. Mario has not been tested to see if he inherited the Huntington allele from his father. Mario's wife Min is pregnant with their son (Min's family has no history of this disease). What is the probability that their first child will develop Huntington's disease?

Explanation / Answer

Huntington disease is an autosomal dominant genetic disorder. The Huntington disease gene is dominant, which means that each child of a parent with Huntington disease has a 50% chance of inheriting the disease and is said to be “at-risk”.

Males and females have the same risk of inheriting the disease. If a person does not inherit the defective gene from the affected parent they can't pass it on to their own children.

The defective gene may be passed from parent to child at conception. If a parent has the gene, each son or daughter has a one in two (50/50) chance of inheriting Huntington's disease.

1. Mario father has Huntington disease. So he has 50% chance of inheriting the disease and is said to be “at-risk”

2. Mario has not been tested to see if he inherited the Huntington allele from his father. Even he has 50% chance of inheriting the disease. Because his father is already a diseased person.

Huntington's disease is an autosomal dominant genetic disorder it is not linked with sex chromosomes.

So even Mario's wife Min is pregnant and her family has no history of this disease, still the child have the possibility of suspecting the the Huntington's disease inherited from his father.

If Mario is diagnosed and found to have Huntington disease his son will definitely 50% to get the disease.

If Mario is diagnosed and found to not have Huntington disease his son will definitely no chance to get the disease.

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