Amelogenesis imperfecta phenotype-genotype correlations with two amelogenin gene mutations

Area of Science:

• Genetics
• Biochemistry
• Developmental Biology

Background:

• Amelogenin is the primary matrix protein in developing dental enamel, crucial for its formation.
• Mutations in the AMELX gene encoding amelogenin cause X-linked amelogenesis imperfecta (AI), presenting as hypoplastic and/or poorly mineralized enamel.
• Eight AMELX mutations have been previously identified.

Purpose of the Study:

• To investigate the genotype and phenotype correlations in two families with X-linked AI.
• To identify novel mutations in the AMELX gene and their effects on enamel formation.

Main Methods:

• DNA analysis of affected individuals and family members.
• Amplification and sequencing of exons 1-7 of the AMELX gene.
• Genotype-phenotype correlation analysis.

Main Results:

• Family 1: A single-base-pair substitution (A-->T at nucleotide 256) in AMELX resulted in a His-->Leu amino acid change, leading to yellowish-brown, poorly mineralized enamel.
• Family 2: A single-nucleotide deletion (C-nucleotide in codon 119) caused a frameshift and premature stop codon, truncating the amelogenin protein by 18 amino acids, resulting in thin, hypoplastic enamel.
• Heterozygous females in both families exhibited vertical hypoplastic grooves.

Conclusions:

• The C-terminus of amelogenin is critical for regulating enamel thickness; mutations affecting this region lead to hypoplastic enamel.
• Mutations elsewhere in AMELX may primarily cause enamel mineralization defects.
• Genotype-phenotype variability in X-linked AI is influenced by the specific location and type of AMELX mutation.