Your preceptor is planning a training session for all new nurses to review principles of genetics and genomics using data from a three-generation family pedigree. The preceptor asks for your help building a genogram to demonstrate patterns of inheritance. You agree to do some reading, describe a genetic disorder, and provide a genogram that would indicate how this disorder is transferred over generations. Your preceptor asks you to pick one disorder from the list below:
Duchenne Muscular Dystrophy
Hemochromatosis
Neurofibromatosis
Hemophilia A
Tay-Sachs disease
Von Willebrand Disease
X-linked adrenoleukodystrophy
Instructions
Include this content in your Word document:
Description of the selected genetic disorder, including clinical manifestations and pattern of inheritance.
A three-generation family pedigree and genogram with standard symbols and terminology.
Analysis of the pedigree and genogram, including:
Identification of affected and carrier individuals
Actual and potential health risks
Explanation of the methods of genetic testing for the selected disorder.
Description of the educational needs of the client and family, including specific examples and supporting rationales.
Three-Generation Family Genogram for Hemophilia A
This genogram illustrates the inheritance pattern of Hemophilia A. Squares represent males, and circles represent females. A filled-in symbol indicates an affected individual, while a symbol with a dot inside indicates a carrier. A line between a square and a circle represents a couple, and a vertical line extending from them connects to their children.
Generation I: The grandfather is unaffected, and the grandmother is a carrier. They have two children.
Generation II: Their son is affected (indicated by a filled-in square), as he inherited the X chromosome with the mutated gene from his carrier mother. Their daughter is a carrier (indicated by a circle with a dot), as she inherited one normal X chromosome from her father and one mutated X chromosome from her mother. She is partnered with an unaffected male.
Generation III: The carrier daughter and her unaffected partner have children. Their son is affected, having inherited the mutated X chromosome from his carrier mother. Their daughter is also a carrier, having inherited one mutated X chromosome from her mother.
Analysis of the Pedigree and Genogram
Affected Individuals: The affected individuals are the males in the second and third generations who have inherited the mutated X chromosome. They exhibit the symptoms of hemophilia.
Carrier Individuals: The carrier individuals are the females in the first, second, and third generations who have one normal X chromosome and one with the mutated gene. They do not typically show symptoms but can pass the disorder to their children.
Actual and Potential Health Risks: The primary health risks for affected individuals include recurrent bleeding episodes, which can lead to joint damage, chronic pain, and disability. There is also a risk of life-threatening internal bleeding. For female carriers, while they are typically asymptomatic, they may experience mild bleeding issues. The potential health risk for a family with this inheritance pattern is that each male child of a carrier female has a 50% chance of being affected, and each female child has a 50% chance of being a carrier.
Methods of Genetic Testing
Genetic testing for Hemophilia A typically involves several methods:
Factor VIII Assay: This is a blood test that measures the amount of functional factor VIII in the blood. Low levels confirm a diagnosis of hemophilia.
DNA Analysis: This is the most definitive method. It involves a blood or saliva sample to look for specific mutations in the F8 gene on the X chromosome. This can be used for:
Carrier testing: To identify females who are carriers of the gene.
Prenatal diagnosis: To determine if a fetus has the disorder.
Newborn screening: To diagnose the disorder shortly after birth.
Educational Needs of the Client and Family
The educational needs for clients and their families with Hemophilia A are extensive and crucial for managing the disorder and preventing complications.
Understanding the Disorder and its Inheritance:
Rationale: Clients and their families need to understand that Hemophilia A is an X-linked recessive disorder so they can grasp the risks to other family members and make informed family planning decisions.
Example: A nurse should use the genogram to visually explain how the disorder is passed down, emphasizing that sons of carrier mothers have a 50% chance of being affected and daughters have a 50% chance of being carriers.
Sample Answer
Genetic Disorder: Hemophilia A
Hemophilia A is a rare, inherited bleeding disorder in which the blood doesn't clot properly. This is due to a deficiency in or a defect of a protein called factor VIII, which is a crucial component of the clotting cascade. The severity of the disorder depends on the amount of functional factor VIII present in the blood; individuals with less than 1% are considered to have severe hemophilia, while those with 5% to 40% have mild hemophilia. Clinical manifestations include spontaneous bleeding into joints and muscles, prolonged bleeding after injury or surgery, and easy bruising. In severe cases, bleeding can occur in critical areas like the brain, which can be life-threatening. The pattern of inheritance is X-linked recessive. This means the gene responsible for the disorder is located on the X chromosome. Because males have only one X chromosome, they are affected if they inherit the mutated gene. Females have two X chromosomes, so they are