09-10-2007, 12:19 PM
2-year-old boy presents with delayed speech development and facial muscle weakness characterized by ptosis, slow closing of eyes, and slow eye movements. Examination also reveals weak masseters, sternocleidomastoids, and temporalis muscles. The physician also notes similarities in the mother's presentation; she relates she has some weakness in her distal arms, and sometimes her hands do not want to open from a closed position. She also relates she has a cataract developing. The physician observes the red and green iridescent posterior subcapsular cataract with a slit lamp . The child is diagnosed with congenital myotonic dystrophy and a mutation in the dystrophia myotonica protein kinase (DMPK) gene. What is the most likely mutation in the DMPK gene in this child?
A. Deletion of the entire gene coding region
B. CTG triplet amplification at the 3™ end
C. Insertion of polyglutamate in the coding region
D. Point mutation in the promoter region
E. Splice-site mutation near the 5™ end
A. Deletion of the entire gene coding region
B. CTG triplet amplification at the 3™ end
C. Insertion of polyglutamate in the coding region
D. Point mutation in the promoter region
E. Splice-site mutation near the 5™ end