title: Truncating CLCN1 mutations in myotonia congenita: variable patterns of inheritance.
abstract: BACKGROUND
  Myotonia congenita due to protein truncating CLCN1 mutations is associated with variable patterns of inheritance.
  
  
  METHODS
  Three family kindreds are described, all of whom possess protein truncating mutations (Y33X, fs503X, R894X). One lineage also has coexistent R894X, A313T, and A320V mutations.
  
  
  RESULTS
  The Y33X mutation kinship has autosomal recessive inheritance and a severe phenotype when homozygous. The fs503X family has autosomal dominant inheritance and a moderate-to-severe phenotype. The A313T mutation kindred also has autosomal dominant inheritance but expresses a mild phenotype, except for the more severely affected compound heterozygotes.
  
  
  CONCLUSIONS
  Early truncating mutations precluding dimerization are expected to be autosomal recessive and express a severe phenotype, while later mutations may be variable. The pedigrees presented here demonstrate that intrafamilial phenotypic variability may result from a dosage effect of an additional mutation, not necessarily variable expressivity. Mutations that have unexpected patterns of inheritance may represent allelic variability.
authors.affiliation: Division of Pediatric Neurology, Departments of Neurology and Pediatrics, University of Washington, and Seattle Children's Hospital, 4800 Sand Point Way NE, Neurology, MB.7.420, Seattle, Washington, USA, 98105.
authors.forename: Randal C
authors.initials: RC
authors.lastname: Richardson
authors.forename: Jack C
authors.initials: JC
authors.lastname: Tarleton
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Bird
authors.forename: Sidney M
authors.initials: SM
authors.lastname: Gospe
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D018118:Chloride Channels / Q000235:genetics*; D005260:Female; D006801:Humans; D040582:Inheritance Patterns / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics*; D009224:Myotonia Congenita / Q000175:diagnosis* / Q000235:genetics*; D010375:Pedigree; D055503:Protein Multimerization / Q000235:genetics
chemical_list: C086321:CLC-1 channel; D018118:Chloride Channels
keywords: CLC-1; CLCN1; allelic variability; myotonia; myotonia congenita