Genetic Disorders: Huntington's and Duchenne Muscular Dystrophy

What is the genetic basis of Huntington's disease?

• It is caused by a deletion of a segment on chromosome 21.

• It is caused by trinucleotide repeats in the HTT gene on chromosome 4.

• It is caused by a duplication of the DMD gene on the X chromosome.

• It is caused by a translocation between chromosomes 5 and 7.

Answer explanation

Huntington's disease is caused by an expansion of CAG trinucleotide repeats in the HTT gene located on chromosome 4. This genetic mutation leads to the production of a toxic protein, resulting in the disease's symptoms.

What is the primary cause of muscle degeneration in Duchenne muscular dystrophy?

• Lack of oxygen supply to muscles

• Deficiency of dystrophin protein

• Excessive calcium in muscle cells

• Overproduction of lactic acid

Answer explanation

The primary cause of muscle degeneration in Duchenne muscular dystrophy is the deficiency of dystrophin protein, which is crucial for maintaining muscle cell integrity. Without it, muscle fibers become damaged and degenerate.

Which of the following is a non-motor symptom of Huntington's disease?

• Muscle spasms

• Cognitive decline

• Joint pain

• Skin lesions

Answer explanation

Cognitive decline is a non-motor symptom of Huntington's disease, affecting thinking and memory. In contrast, muscle spasms, joint pain, and skin lesions are more related to motor symptoms or other conditions.

What is the mode of inheritance for Duchenne muscular dystrophy?

• X-linked recessive

• X-linked dominant

• Autosomal dominant

• Autosomal recessive

Answer explanation

Duchenne muscular dystrophy is inherited in an X-linked recessive manner, meaning the gene responsible is located on the X chromosome. Males, having one X chromosome, are more severely affected, while females can be carriers.

Which of the following is a potential future treatment for Huntington's disease currently under research?

• Gene therapy

• Radiation therapy

• Blood transfusion

• Hormone replacement therapy

Answer explanation

Gene therapy is a promising area of research for Huntington's disease, aiming to bypass the genetic mutations causing the disorder. Other options like radiation therapy, blood transfusion, and hormone replacement therapy are not relevant treatments.

At what age do symptoms of Duchenne muscular dystrophy typically begin to appear?

• At birth

• Around 2-3 years old

• In teenage years

• In late adulthood

Answer explanation

Symptoms of Duchenne muscular dystrophy typically begin to appear around 2-3 years old, as this is when children start to show delays in motor skills and muscle weakness.

Huntington's disease is inherited in which pattern?

• Autosomal recessive

• X-linked recessive

• Autosomal dominant

• Mitochondrial

Answer explanation

Huntington's disease is inherited in an autosomal dominant pattern, meaning only one copy of the mutated gene from an affected parent can cause the disease in offspring.

What is the role of dystrophin in muscle cells?

• It provides energy to muscle cells.

• It helps in muscle contraction.

• It stabilises muscle cell membranes.

• It transports oxygen to muscles.

Answer explanation

Dystrophin is crucial for stabilising muscle cell membranes by linking the cytoskeleton to the extracellular matrix. This function helps protect muscle cells from damage during contraction, making it the correct choice.

Which protein is primarily affected in Huntington's disease?

• Myosin

• Actin

• Huntingtin

• Dystrophin

Answer explanation

Huntington's disease is caused by a mutation in the HTT gene, which encodes the huntingtin protein. This protein is primarily affected, leading to the neurodegenerative symptoms associated with the disease.

Which chromosome is affected in Duchenne Muscular Dystrophy (DMD)?

• Chromosome 21

• Chromosome 4

• Chromosome 7

• Chromosome X

Answer explanation

Duchenne Muscular Dystrophy (DMD) is caused by mutations in the dystrophin gene, which is located on the X chromosome. This X-linked recessive disorder primarily affects males.