Intellectual Disability: History Repeats Itself

Excerpt

To the Editor: A previously healthy eight-year-old girl, second born to non-consanguineous parents, presented with poor scholastic skills for last 3y. She was clumsy in class with reduced interaction with peers. Her academic grades were below par and she had significant trouble in recall and learning new things. She was disorganized and had difficulty following directions. Her perinatal period was uneventful. Her developmental milestones were age appropriate except for expressive and receptive language domains. Restricted interests and repetitive behavior was not noted. Her family history was instructive (Fig. 1) and each subsequent generation was affected at an early age, suggesting autosomal dominant inheritance with anticipation. Her maternal grandfather developed intermittent hand stiffness on activity from 50 y. He underwent bilateral cataract surgery at 55 y. The stiffness was progressive and he became non-ambulant by 60 y. Her mother and maternal uncle also have similar concerns of activity-induced hand stiffness from 27 and 17 y of age. In addition, the index child had a younger sibling with antenatal polyhydramnios who succumbed to respiratory failure on day 1 of life. Motor examination was unremarkable; did not reveal any selective muscle wasting or myotonia. Distal muscle wasting with myotonia on percussion was noted in the mother. Her psychometric performance showed an Intelligent Quotient of 60 on the Malins Intelligence Scale for Indian Children. The clinical diagnosis of Myotonic Dystrophy was confirmed by expanded CTG repeats (Normal 5–36) in the DMPK gene by triplet primed Polymerase Chain Reaction analysis.

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