AMELX Mutations and Genotype–Phenotype Correlation in X-Linked Amelogenesis Imperfecta
International Journal of Molecular Sciences, vol.25, no.11, 2024 (SCI-Expanded, Scopus)
- Publication Type: Article / Article
- Volume: 25 Issue: 11
- Publication Date: 2024
- Doi Number: 10.3390/ijms25116132
- Journal Name: International Journal of Molecular Sciences
- Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Academic Search Premier, CAB Abstracts, EMBASE, Food Science & Technology Abstracts, MEDLINE, Veterinary Science Database, Directory of Open Access Journals
- Keywords: ameloblast, amelogenin, apoptosis, biomineralization, dental enamel, ER stress, lyonization, protein secretion, signal peptide, unfolded protein response
- Open Archive Collection: AVESIS Open Access Collection
- Istanbul University Affiliated: Yes
Abstract
AMELX mutations cause X-linked amelogenesis imperfecta (AI), known as AI types IE, IIB, and IIC in Witkop’s classification, characterized by hypoplastic (reduced thickness) and/or hypomaturation (reduced hardness) enamel defects. In this study, we conducted whole exome analyses to unravel the disease-causing mutations for six AI families. Splicing assays, immunoblotting, and quantitative RT-PCR were conducted to investigate the molecular and cellular effects of the mutations. Four AMELX pathogenic variants (NM_182680.1:c.2T>C; c.29T>C; c.77del; c.145-1G>A) and a whole gene deletion (NG_012494.2:g.307534_403773del) were identified. The affected individuals exhibited enamel malformations, ranging from thin, poorly mineralized enamel with a “snow-capped” appearance to severe hypoplastic defects with minimal enamel. The c.145-1G>A mutation caused a -1 frameshift (NP_001133.1:p.Val35Cysfs*5). Overexpression of c.2T>C and c.29T>C AMELX demonstrated that mutant amelogenin proteins failed to be secreted, causing elevated endoplasmic reticulum stress and potential cell apoptosis. This study reveals a genotype–phenotype relationship for AMELX-associated AI: While amorphic mutations, including large deletions and 5′ truncations, of AMELX cause hypoplastic-hypomaturation enamel with snow-capped teeth (AI types IIB and IIC) due to a complete loss of gene function, neomorphic variants, including signal peptide defects and 3′ truncations, lead to severe hypoplastic/aplastic enamel (AI type IE) probably caused by “toxic” cellular effects of the mutant proteins.