Mr. Wayne is a 38-year-old man with a significant family history of elevated cho

Question

Mr. Wayne is a 38-year-old man with a significant family history of elevated cholesterol levels. His father died at age 42 from a massive heart attack secondary to elevated cholesterol and triglycerides, and two of his older siblings are currently taking medications to lower their cholesterol levels. Mr. Wayne makes an appointment to discuss his risk for hypercholesterolemia. The nurse recognizes that Mr. Wayne is at risk for familial hypercholesterolemia because this is an autosomal dominant inherited condition. (Learning Objective 2)

Describe the pattern of autosomal dominant inheritance.

Mr. Wayne asks what chance his children have of developing familial hypercholesterolemia. How should the nurse respond?

Explain the phenomenon of penetrance observed in autosomal dominant inheritance.

Explanation / Answer

Pattern of autosomal dominant inheritance:

Some genetic conditions are caused by mutation in a single gene.These conditions are usually inherited in one of several patterns,depending on the gene involved.One of them is autosomal dominant.

In autosomal dominant one mutated copy of the gene in each cell is sufficient for a person to be affected by an autosomal dominant disorder.In some cases,an affected person inherits the condition form an affected parent.In others,the condition may result from a new mutation in the gene and occur in people with no history of the disorder in their family.

Examples for autosomal dominant:

Huntington disease,marfan syndrome.

In an autosomal dominant disorder,the mutated gene is dominant gene located on one of the nonsex chromosomes(autosomes).You may need only one mutated gene to be affected by this type of disorder.A person with an autosomal dominant disorder -in this case,the father has a fifty percent chance of having an affected child with one mutated gene nd a 50 percent chance of having an unaffected child with two normal genes(recessive gene).

familial hypercholesterolemia:

Children with one parent with FH(Familial Hypercholesterolemia) have 50 percent chance of inheriting heterozygous FH(heFH).

If both parents have FH,their children are at rik for a more serious form of disease,homozygous FH.(HoFH).In addition to the 50 percent cahnce of inheriting one FH gene from one parent,these children have a 25 percent chance of of inheriting 2 FH genes,one from each affected parent.Homozygous FH is more aggressive form of the disorder.

Both types of FH lead to early heart disease caused by narrowing or blocked arteries and plaques,including heart attacks,strokes,bypass,angina,stents and congestive heart failure.

Phenomenon of penetrance observed in autosomal dominant inheritance:

Penetrance in genetics is the proportion of individuals carrying particular varient (or allele) of a gene(the genotype)that also express an associated trait (the phenotype).In medical genetics,the penetrance of a disease causing mutation is the proportion of individuals with the mutation who exhibit clinical symptoms.Ex:if a mutation in the gene responsible for particular autosomal dominant disorder has 95% penetrance,then 95% of those with the mutation will develop the disease,while 5% will not.

A condition,most commonly inherited in an autosomal dominant manner,is said to show complete penetrance if clinical symptoms are present in all individuals who have the disease causing mutations.

Autosomal dominant inheritance occurs when one allele of a heterozygous pair causes a phenotypic trait.Many classic human genetic disorders are caused by this mechanism and follow this pattern.

Human autosomal dominant diseases are extremely rare conditions in which affected individuals are heterozygotes.Many of this heterozygous genotypes exhibit incomplete penetrance.For this set of rare conditions,the penetrance rate is therefore understood as the probability of heterozygote presenting the disease.

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