Genetics and Disease Practice Questions

Q: Which one of the following is an autosomal recessive disorder?

Cystic fibrosis. ***Cystic fibrosis*** - **Cystic fibrosis** is caused by mutations in the **CFTR gene**, leading to defective **chloride channel** function. - It is an **autosomal recessive disorder**, meaning an individual must inherit two copies of the mutated gene (one from each parent) to be affected. *Huntington's disease* - **Huntington's disease** is an **autosomal dominant disorder** caused by a mutation in the HTT gene. - Only one copy of the mutated gene is sufficient to cause the disease, resulting in progressive neurodegeneration. *Marfan syndrome* - **Marfan syndrome** is an **autosomal dominant disorder** affecting connective tissue, caused by mutations in the FBN1 gene. - It results in skeletal, ocular, and cardiovascular abnormalities due to defective **fibrillin-1**. *Neurofibromatosis type 1* - **Neurofibromatosis type 1** is an **autosomal dominant disorder** caused by mutations in the NF1 gene. - It is characterized by multiple neurofibromas, café-au-lait macules, and Lisch nodules.

Q: What is the mode of inheritance for the most common form of hypophosphatemic rickets?

X-Linked Dominant (XD). ***X-Linked Dominant (XD)*** - The most common form of hypophosphatemic rickets is **X-linked hypophosphatemic rickets (XLH)**, which is inherited in an X-linked dominant pattern. - This condition is caused by mutations in the **PHEX gene** on the X chromosome, leading to impaired phosphate reabsorption in the kidneys. *Autosomal Recessive (AR)* - While some rare forms of hypophosphatemic rickets exist with **autosomal recessive** inheritance, they are not the most common. - These forms typically involve mutations in genes affecting phosphate transport or vitamin D metabolism, distinct from the primary defect in XLH. *Autosomal Dominant (AD)* - There are also rare **autosomal dominant** forms of hypophosphatemic rickets, such as hereditary hypophosphatemic rickets with hypercalciuria (HHRH) or autosomal dominant hypophosphatemic rickets (ADHR). - However, these are less common than the X-linked dominant form (XLH). *X-Linked Recessive (XR)* - **X-linked recessive** inheritance typically affects males more severely and exclusively, with carrier females usually unaffected or mildly affected. - In X-linked dominant conditions like XLH, both males and females are affected, though females may exhibit variable expressivity.

Q: Which of the following statements is NOT true about Alport's syndrome?

It is caused by mutations in type I collagen.. ***It is caused by mutations in type I collagen.*** - Alport's syndrome is primarily caused by mutations in genes encoding **type IV collagen**, not type I collagen [1]. - These mutations lead to defects in the **glomerular basement membrane**, inner ear, and eye [1]. *It is inherited in an X-linked pattern.* - The most common form of Alport's syndrome (around 85%) is inherited in an **X-linked recessive pattern**, due to mutations in the *COL4A5* gene. - This means males are typically more severely affected than females. *It causes nerve deafness.* - Individuals with Alport's syndrome often develop **sensorineural hearing loss**, which is a form of nerve deafness. - This symptom usually progresses from high-frequency hearing loss to profound deafness. *It leads to glomerulonephritis.* - The characteristic renal feature of Alport's syndrome is a progressive **glomerulonephritis**, eventually leading to **end-stage renal disease (ESRD)**. - This is due to the structural defects in the **glomerular basement membrane**, causing hematuria and proteinuria [1].

Q: Which of the following conditions is associated with ectopia lentis?

Homocystinuria. ***Homocystinuria*** - **Ectopia lentis** (lens dislocation) is a common and characteristic ocular manifestation of homocystinuria. - The lens typically dislocates **downward and inward**, differentiating it from Marfan syndrome. *Alport syndrome* - Characterized by **glomerulonephritis**, **sensorineural hearing loss**, and ocular abnormalities. - Ocular manifestations include **anterior lenticonus** (which can be mistaken for ectopia lentis in some descriptions), posterior polymorphous corneal dystrophy, and retinal flecks, but not classic ectopia lentis. *Lowe syndrome* - Also known as oculocerebrorenal syndrome of Lowe, it primarily affects the **eyes, brain, and kidneys**. - Ocular features include **congenital cataracts** and glaucoma, but not ectopia lentis. *Sulphite oxidase deficiency* - This is a rare metabolic disorder affecting the metabolism of sulfur-containing amino acids, leading to severe neurological symptoms. - While it can manifest with **cataracts** and **lens subluxation** in some cases, ectopia lentis is more characteristically associated with homocystinuria, and the overall clinical picture of sulphite oxidase deficiency is dominated by severe neurological impairment.

Q: What is the complete classic triad of findings that defines Young's syndrome?

Azoospermia, bronchiectasis, and chronic sinusitis. ***Azoospermia, bronchiectasis, and chronic sinusitis*** - Young's syndrome is characterized by the triad of **azoospermia** (due to obstructive epididymal dysfunction), **bronchiectasis**, and **chronic sinusitis** [1]. - This syndrome primarily affects **middle-aged men** and is often mistaken for cystic fibrosis due to similar respiratory symptoms. *Azoospermia, asthma, and chronic rhinitis* - This option incorrectly lists **asthma** and **chronic rhinitis** instead of bronchiectasis and chronic sinusitis. - While respiratory symptoms are part of Young's syndrome, specifically **bronchiectasis** and **sinusitis** are key [1]. *Oligospermia, bronchiectasis, and chronic sinusitis* - This option is incorrect because Young's syndrome is defined by **azoospermia** (complete absence of sperm), not just **oligospermia** (low sperm count). - The obstructive nature of the epididymal dysfunction in Young's syndrome leads to a complete lack of sperm. *Azoospermia, chronic bronchitis, and nasal polyps* - This option incorrectly identifies **chronic bronchitis** and **nasal polyps** as part of the classic triad. - The correct respiratory components are **bronchiectasis** and **chronic sinusitis**, which signify persistent inflammation and structural lung changes rather than simply bronchitis.

Q: Which condition is associated with calcification of the intervertebral disc?

Alkaptonuria. ***Alkaptonuria*** - **Alkaptonuria** is a rare autosomal recessive disorder characterized by a deficiency of the enzyme **homogentisate 1,2-dioxygenase**, leading to the accumulation of **homogentisic acid**. - This accumulation results in the deposition of a **dark pigment (ochre pigment)** in connective tissues, including the intervertebral discs, causing **calcification (ochronosis)** and early degenerative arthritis. *Gout* - **Gout** is caused by the deposition of **monosodium urate crystals** in joints and soft tissues, leading to inflammation and pain [1]. - While it can affect various joints, it does not typically cause **calcification of intervertebral discs**; rather, it can form tophi in periarticular soft tissues [1]. *Rheumatoid* - **Rheumatoid arthritis** is a chronic autoimmune inflammatory disease primarily affecting the **synovial lining of joints**, leading to joint destruction and deformity. - It does not involve the **calcification of intervertebral discs**; spinal involvement is usually restricted to the cervical spine, particularly the atlantoaxial joint. *Psoriasis* - **Psoriasis** is a chronic inflammatory skin condition, which in some cases can be associated with **psoriatic arthritis**, an inflammatory arthritis. - Psoriatic arthritis primarily affects peripheral joints, the sacroiliac joints, and the spine, but it does not cause **calcification of the intervertebral discs** as seen in alkaptonuria.

Q: Which one of the following diseases is classified as an autosomal dominant disorder?

Maturity onset diabetes of the young. ***Maturity onset diabetes of the young*** - **Maturity onset diabetes of the young (MODY)** is a genetically heterogeneous group of single-gene disorders characterized by beta-cell dysfunction and impaired insulin secretion, typically inherited in an **autosomal dominant pattern** [1]. - A single copy of the mutated gene is sufficient to cause the condition, leading to diabetes usually before the age of 25, often without obesity or autoantibodies [1]. *Hemochromatosis* - **Hemochromatosis** is typically inherited in an **autosomal recessive pattern**, meaning two copies of the mutated gene (e.g., *HFE* gene) are required for the disease to manifest. - It leads to excessive iron absorption and tissue iron overload. *Phenylketonuria* - **Phenylketonuria (PKU)** is an **autosomal recessive disorder** caused by a deficiency in the enzyme **phenylalanine hydroxylase**, necessitating two mutated gene copies for the disease to occur. - This leads to the accumulation of phenylalanine, causing neurological damage if untreated. *Glucose-6 phosphate dehydrogenase deficiency* - **Glucose-6 phosphate dehydrogenase (G6PD) deficiency** is an **X-linked recessive disorder**, meaning the gene is located on the X chromosome and typically affects males more severely. - Females can be carriers, and hemizygous males (having only one X chromosome) will express the disorder if they inherit the mutated gene.

Question 1

Which one of the following is an autosomal recessive disorder?

Accepted Answer

Cystic fibrosis

Answer

Huntington's disease

Answer

Marfan syndrome

Answer

Neurofibromatosis type 1

Question 2

What is the mode of inheritance for the most common form of hypophosphatemic rickets?

Accepted Answer

X-Linked Dominant (XD)

Answer

Autosomal Recessive (AR)

Answer

Autosomal Dominant (AD)

Answer

X-Linked Recessive (XR)

Question 3

Which of the following statements is NOT true about Alport's syndrome?

Accepted Answer

It is caused by mutations in type I collagen.

Answer

It is inherited in an X-linked pattern.

Answer

It causes nerve deafness.

Answer

It leads to glomerulonephritis.

Question 4

Which of the following conditions is associated with ectopia lentis?

Accepted Answer

Homocystinuria

Answer

Alport syndrome

Answer

Lowe syndrome

Answer

Sulphite oxidase deficiency

Question 5

What is Reifenstein syndrome?

Accepted Answer

Partial androgen insensitivity syndrome due to receptor mutation.

Answer

Complete androgen insensitivity syndrome with female external genitalia

Answer

5-alpha reductase deficiency causing ambiguous genitalia

Answer

Gonadal dysgenesis with streak gonads

Question 6

What is the complete classic triad of findings that defines Young's syndrome?

Accepted Answer

Azoospermia, bronchiectasis, and chronic sinusitis

Answer

Oligospermia, bronchiectasis, and chronic sinusitis

Answer

Azoospermia, asthma, and chronic rhinitis

Answer

Azoospermia, chronic bronchitis, and nasal polyps

Question 7

Which condition is associated with calcification of the intervertebral disc?

Accepted Answer

Alkaptonuria

Answer

Gout

Answer

Rheumatoid

Answer

Psoriasis

Question 8

Which syndrome is characterized by oro-cutaneous hamartomatous tumors, gastrointestinal polyps, and abnormalities of the breast, thyroid gland, and genitourinary system?

Accepted Answer

Cowden's syndrome - a genetic disorder involving multiple hamartomas and systemic abnormalities, including breast, thyroid, and genitourinary systems.

Answer

Juvenile polyposis - involves juvenile polyps in the gastrointestinal tract, without systemic hamartomas.

Answer

Peutz-Jeghers syndrome - features pigmented lesions and gastrointestinal hamartomas, without systemic involvement.

Answer

Familial adenomatous polyposis (FAP) - involves multiple adenomatous polyps and a high risk of colorectal cancer.

Question 9

A 43-year-old man who had a subarachnoid hemorrhage from an intracranial aneurysm 8 years ago and has also experienced progressive renal impairment associated with hematuria is most likely to have which diagnosis?

Accepted Answer

A genetic disorder causing renal cysts and associated with intracranial aneurysms

Answer

A genetic condition causing hypertension due to sodium retention

Answer

A condition characterized by cystic dilation of renal pyramids

Answer

An autoimmune condition causing glomerulonephritis and pulmonary hemorrhage

Question 10

Which one of the following diseases is classified as an autosomal dominant disorder?

Accepted Answer

Maturity onset diabetes of the young

Answer

Hemochromatosis

Answer

Phenylketonuria

Answer

Glucose-6 phosphate dehydrogenase deficiency

Genetics and Disease — MCQs

Genetics and Disease — MCQs

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