Answer to Question #165678 in Genetics for Virat

Question

1) A.I., a 6-year-old boy, is undergoing examination due to a slight developmental delay. He has

difficulty climbing stairs, running, has reduced physical strength and low endurance during intense physical

exercise. Muscle biopsy results showed a pronounced change in muscle fiber size.

Based on these results, the child has a preliminary diagnosis of having Duchene muscular dystrophy

(DMD). Duchene muscular dystrophy is a serious recessive disease linked to the X chromosome, which is

characterized by the rapid progression of muscular dystrophy, which ultimately leads to a complete loss of

the patient’s ability to move and consequent death.

To confirm diagnosis and determine the mutation in the dystrophic gene in A.I, DNA diagnostics

were performed. Aberrations were found in the coding part of the gene

Questions for discussion:

1. What type of mutation causes Duchene muscular dystrophy?

2. Describe the mechanism of mutation occurrence. What are the consequences of this mutation?

3. Determine the genotypes of parents and the patient.

4. Determine the risks for the next child to have the same illness.

Answer 1

1.   What type of mutation causes Duchene muscular dystrophy?

Duchenne muscular dystrophy is inherited in an X-linked recessive pattern. Males have only one copy of the X chromosome from their mother and one copy of the Y chromosome from their father. If their X chromosome has a DMD gene mutation, they will have Duchenne muscular dystrophy.

2.   Describe the mechanism of mutation occurrence. What are the consequences of this mutation?

In Duchenne, the error occurs in the instructions used to make a protein called dystrophin. Dystrophin is needed by muscles in the body to protect them as they contract and relax. Children with Duchenne are unable to make the dystrophin protein, which causes their muscles to weaken over time.

3.   Determine the genotypes of parents and the patient.

A duplication of exons 8 through 9 of the dystrophin gene in both the patient and the mother. The muscle biopsy of the patient has partial expression of the dystrophin protein.

4. Determine the risks for the next child to have the same illness

This is a sporadic mutation occurring in the grand maternal lineage. Genotype–Phenotype Correlations. Dystrophinopathy phenotypes are dependent on the degree to which the dystrophin gene, DMD, is affected by the mutation. Complete loss of DMD function leads to DMD, while relatively mild disruption of DMD function leads to BMD. The risks associated for the next child with the same illness include;

·        Underweight;

·        Poorer lung function, measured in terms of the highest pressure during inhalation;

·        Higher levels of proteins in the blood that indicate the heart is damaged or weakened;

·        Trouble walking. Some people with muscular dystrophy eventually need to use a wheelchair;

·        Trouble using arms;

·        Shortening of muscles or tendons around joints (contractures);

·        Breathing problems;

·        Curved spine (scoliosis);

·        Heart problems and;

·        Swallowing problems.