Question 1

Q: A 4-year-old boy presents to his pediatrician for severe developmental delay. On exam he is noted to have macroorchidism, hypertelorism, large protruding ears, a large jaw, and a long thin face. Suspicious of what the diagnosis may be, the pediatrician orders a PCR and DNA sequencing. The results reveal an expansion of 250 repeats of CGG. What is the diagnosis of the boy?

Fragile X syndrome. ***Fragile X syndrome*** - The combination of **developmental delay**, characteristic physical features (**macroorchidism, large protruding ears, long thin face, large jaw**), and a **CGG repeat expansion** (250 repeats) is pathognomonic for Fragile X syndrome. - This is an **X-linked disorder** caused by an expansion of CGG trinucleotide repeats in the *FMR1* gene, leading to reduced or absent fragile X mental retardation protein (FMRP). *Huntington's disease* - Characterized by **chorea**, psychiatric symptoms, and cognitive decline, typically manifesting in adulthood, not early childhood developmental delay. - Caused by a **CAG trinucleotide repeat expansion** in the *HTT* gene, not CGG. *Spinal and bulbar muscular atrophy* - This is an **X-linked recessive** neurodegenerative disorder leading to muscle weakness and atrophy, which usually presents in adulthood. - It is caused by a **CAG repeat expansion** in the androgen receptor gene. *Myotonic dystrophy type 1* - Presents with progressive **muscle wasting and weakness**, myotonia, cataracts, and cardiac conduction defects, typically later in childhood or adulthood. - Caused by a **CTG trinucleotide repeat expansion** in the *DMPK* gene. *Friedreich ataxia* - Characterized by progressive **ataxia**, dysarthria, and loss of vibration/proprioception, usually beginning in childhood or adolescence. - Caused by a **GAA trinucleotide repeat expansion** in the *FXN* gene.

Question

A 4-year-old boy presents to his pediatrician for severe developmental delay. On exam he is noted to have macroorchidism, hypertelorism, large protruding ears, a large jaw, and a long thin face. Suspicious of what the diagnosis may be, the pediatrician orders a PCR and DNA sequencing. The results reveal an expansion of 250 repeats of CGG. What is the diagnosis of the boy?

Accepted Answer

Fragile X syndrome

Answer

Huntington's disease

Answer

Spinal and bulbar muscular atrophy

Answer

Myotonic dystrophy type 1

Answer

Friedreich ataxia

Genetic and Metabolic Disorders — MCQs

Genetic and Metabolic Disorders — MCQs

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