Proximal myotonic myopathy. Clinical features of a multisystem disorder similar to myotonic dystrophy
K. Ricker, M. C. Koch, F. Lehmann-Horn, D. Pongratz, N. Speich, K. Reiners, C. Schneider and R. T. Moxley 3rd
Department of Neurology, University of Wurzburg, Germany.
BACKGROUND: Previous investigations in three families have shown that
proximal myotonic myopathy (PROMM) is not linked to the gene loci for
myotonic dystrophy (DM) or to the loci of the genes of the muscle sodium
and chloride channels associated with other myotonic disorders. It is
important to extend our clinical knowledge of this interesting new disorder
by studying other families. PATIENTS: Thirty-five patients in 14 new
families; 27 patients were examined. METHODS: Clinical examination,
electromyography, muscle biopsy, DNA analysis. RESULTS: The following
findings were noted: proximal without distal weakness of the legs (n = 21);
myotonia on electromyograms (n = 23); intermittent clinical myotonia (n =
17); cataracts (n = 24) and a number of the cataracts were identical to the
type in DM (n = 11); and peculiar muscle pain (n = 14). A few patients had
cardiac arrhythmias, and others had elevations in the concentrations of
serum gamma-glutamyltransferase. None of the patients had significant
muscle atrophy. Muscle biopsy specimens showed mild myopathic changes. All
patients had normal trinucleotide (cytosine, thymine, and guanine) repeat
size of the DM gene in leukocyte DNA. Muscle DNA probes from three patients
showed findings identical to those of their leukocyte DNA probes.
CONCLUSIONS: Proximal myotonic myopathy is a new genetic disorder similar
to, but distinct from, DM. Patients suspected of having DM but with
negative DNA studies may have PROMM. The gene defect for PROMM awaits
discovery. Because of the similarities between PROMM and DM, this discovery
will not only shed light on the pathomechanism of PROMM, but it may also
increase our understanding of DM.