Introduction

Cleidocranial dysplasia (CCD) is an autosomal dominant skeletal disorder associated with features including hypoplasia/aplasia of the clavicles, patent fontanelles, supernumary teeth, and short stature. In one family the mutation was characterized as a duplication of a part of a polyalanine tract which normally comprises 17 residues to 27 alanines. This tract comprises GCG repeats with GCT interruptions. Autosomal dominant oculopharangeal muscular dystophy is an adult-onset disease which typically presents in the sixth decade with progressive swallowing difficulties, ptosis and proximal limb weakness. The presence of typical oculopharangeal muscular dystrophy in an individual homozygous for GCG7 suggests that this allele can cause recessive OPMD. The long alleles are associated with higher levels of insulin mRNA and protein in the thymus, compared with the short alleles. The greater levels of insulin associated with the long alleles are believed to facilitate deletion of insulin-specific T-lymphocytes, which play an important role in the immune response leading to type 1 diabetes.