Novel KLK4 and MMP20 Mutations Discovered by Whole-exome Sequencing

Non-syndromic amelogenesis imperfecta (AI) is a collection of isolated inherited enamel malformations that follow X-linked, autosomal-dominant, or autosomal-recessive patterns of inheritance. The AI phenotype is also found in syndromes. We hypothesized that whole-exome sequencing of AI probands showing simplex or recessive patterns of inheritance would identify causative mutations among the known candidate genes for AI. DNA samples obtained from 12 unrelated probands with AI were analyzed. Disease-causing mutations were identified in three of the probands: a novel single-nucleotide deletion in both KLK4 alleles (g.6930delG; c.245delG; p.Gly82Alafs*87) that shifted the reading frame, a novel missense transition mutation in both MMP20 alleles (g.15390A>G; c.611A>G; p.His204Arg) that substituted arginine for an invariant histidine known to coordinate a structural zinc ion, and a previously described nonsense transition mutation in a single allele of FAM83H (c.1379G>A; g.5663G>A; p.W460*). Erupted molars and cross-sections from unerupted parts of the mandibular incisors of Mmp20 null mice were characterized by scanning electron microscopy. Their enamel malformations closely correlated with the enamel defects displayed by the proband with the MMP20 mutation. We conclude that whole-exome sequencing is an effective means of identifying disease-causing mutations in kindreds with AI, and this technique should prove clinically useful for this purpose.