Hypodontia as an extended phenotype in families with nonsyndromic oral clefts: findings from a 39-family clinical cohort.

INTRODUCTION: Hypodontia is frequent in individuals with nonsyndromic oral clefts (NSOC) and has been proposed as a potential extended phenotype reflecting increased genetic susceptibility. However, hypodontia within the cleft area likely results from local anatomical disruption rather than a shared genetic etiology, limiting its usefulness in recurrence-risk assessment. Hypodontia outside the cleft area, though less prevalent, is more likely to reflect a genetically driven disturbance in odontogenesis and a more meaningful marker of familial susceptibility. OBJECTIVE: In this observational cohort study, we investigated whether parents with NSOC and hypodontia outside the cleft area have a higher rate of cleft recurrence in their offspring compared with parents without hypodontia. METHODOLOGY: From a longitudinal cohort of 358 individuals with NSOC followed at the Hospital for Rehabilitation of Craniofacial Anomalies, Bauru, Brazil, from 2020 to 2022, participants who had biological children were interviewed regarding cleft recurrence and family history. Eligibility criteria included confirmed NSOC, at least one biological child, and availability of panoramic radiographs for hypodontia assessment. RESULTS: Individuals were categorized as NSOC with hypodontia outside the cleft area (CH group) or isolated NSOC without hypodontia (IC group). Thirty-nine families met the inclusion criteria (9 CH; 30 IC). Cleft recurrence proportions were 22.2% in the CH group and 13.3% in the IC group. Descriptive and inferential analyses were performed; Fisher's exact test was employed for comparisons. The estimated relative risk was 1.67 (95% confidence interval [CI]: 0.36-7.66; p=0.607). Although this difference was not statistically significant, the observed phenotypic pattern raises the hypothesis that hypodontia outside the cleft region may represent a potential marker of developmental susceptibility and etiological heterogeneity in NSOC. CONCLUSION: These findings support the value of comprehensive dental phenotyping in craniofacial research and warrant further investigation in larger family-based cohorts integrating phenotypic and genetic approaches.