Defective Msx1 Nuclear Translocation Underlies Severe Oligodontia

This study aimed to elucidate the mechanism by which MSX1 variants contribute to nonsyndromic tooth agenesis (NSTA) and determine how variant domains correlate with tooth loss severity. Two families with NSTA were analyzed using whole-exome and Sanger sequencing. Ethical approval was obtained from the institutional review board. Identified MSX1 variants (p.P247S and p.155fs*) were functionally characterized via bioinformatics analysis and in vitro experiments (Approval Number: 202203062). 293T cells transfected with variant plasmids were assessed for protein localization (immunofluorescence) and expression of tooth development markers (PAX9, BMP4) using quantitative methods. Statistical significance was evaluated using Student’s t-test. Two novel MSX1 variants were identified: p.P247S (9 missing teeth) and p.155fs* (13 missing teeth). The p.155fs* variant disrupted the homeodomain, impaired nuclear entry, and reduced PAX9/BMP4 expression. Severity of tooth loss correlated with variant location, with homeodomain disruption causing the most severe phenotype. MSX1 variants in the homeodomain impair nuclear localization and downregulate key tooth development regulators, leading to severe NSTA. These findings expand the NSTA variant spectrum and provide insights for genetic counseling.