Oculopharyngeal muscular dystrophy (OPMD)
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A 50-year-old French-Canadian man presents with progressive bilateral ptosis and difficulty swallowing. He tilts his head back to see and has lost weight due to dysphagia. His father had similar symptoms starting in his 40s.
AD; PABPN1 (poly(A) binding protein nuclear 1)
- GCN trinucleotide repeat expansion in exon 1
- Normal: 6 repeats; pathogenic: 8-13 repeats (shortest pathogenic repeat of any TNR disorder)
- French-Canadian and Bukharan Jewish founder populations
- AR form exists (homozygous expansions: more severe, earlier onset)
- Late onset (typically 40s-60s): one of the latest-onset muscular dystrophies
- Progressive ptosis (bilateral): often the first symptom
- Progressive dysphagia (pharyngeal muscles): risk of aspiration
- Proximal limb weakness (later, mild)
- Tongue atrophy
- No cardiac involvement (unlike DM1)
- PABPN1 GCN repeat sizing
- Muscle biopsy: intranuclear tubular filaments (characteristic)
- CK mildly elevated
- Surgical ptosis correction (frontalis sling or blepharoplasty)
- Cricopharyngeal myotomy or dilation for dysphagia
- Speech/swallow therapy
- Nutritional support
"OPMD = Old People's Muscle Disease": one of the latest-onset muscular dystrophies (40s-60s), unlike Duchenne (childhood) or FSHD (teens-20s).
"Oculo-Pharyngeal": the name tells you the two key features: eyes (ptosis) and pharynx (dysphagia).
Shortest pathogenic repeat: Only 8-13 GCN repeats needed (vs >200 for Fragile X, >40 for Huntington). Think "OPMD is a short repeat for an old person."
This visual highlights the two cardinal features encoded in the name (ptosis for "Oculo," dysphagia for "Pharyngeal") and the gene mnemonic: "PABPN1 = Ptosis And Bad Pharynx, Poly-A Binding Protein."
