BACKGROUND: Myotonic dystrophy type 2 (DM2) is an autosomal dominant, 
multisystem disorder caused by a CCTG tetranucleotide repeat expansion located 
in intron 1 of the zinc finger protein 9 gene (ZNF9 gene) on chromosome 3q 21.3.
OBJECTIVES: To describe the clinical, electrophysiologic and pathologic findings 
in patients with myotonic dystrophy 2.
METHODS: We evaluated 10 patients genetically, clinically and 
electrophysiologically during the years 2007 to 2008.
RESULTS: All patients were of Jewish European ancestry. Among affected 
individuals, eight patients had symptoms of proximal muscle weakness, two had 
muscle pain, and two exhibited myotonia. On physical examination six patients 
had severe weakness of hip flexor muscles. Seven individuals underwent cataract 
surgery, and cardiac involvement was seen in one case. On the initial 
electromyographic (EMG) examination five patients demonstrated myotonic 
discharges; repeated studies showed these discharges in nine cases. Six muscle 
biopsies showed non-specific pathological changes. Seven patients had an 
affected first-degree relative with either a diagnosed or an undiagnosed 
muscular disorder consistent with an autosomal dominant trait.
CONCLUSIONS: DM2 may often present with proximal muscle weakness without 
myotonia. EMG may initially fail to show myotonic discharges, but these 
discharges may eventually show in most cases on repeated EMG. Thus, DM2 may be 
underdiagnosed and should be included in the differential diagnosis of adult 
patients of Jewish European ancestry presenting with proximal lower limb 
weakness.