Overview of repeats
Mutations in the COMP gene can lead to two diseases: pseudoachondroplasia (PSACH) and a type of multiple epiphyseal dysplasia (MED), both of which are skeletal disorders (Lin et al., 2018). Repeat mutations in COMP gene can cause both diseases, as shown in two patients described by Délot et al. (1999). One affected individual who was diagnosed with a typical PSACH phenotype had 7 repeats of GAC in the allele. The other, patient with a mild MED was carrying an allele with 6 repeats in the same locus (Délot et al., 1999).
Moreover, PSACH patients with a deletion of one GAC repeat has been described, demonstrating the pathogenic effect of contraction of a repeat (Hecht et al., 1995).