Development and Validation of a Prediction Model for Severe Male Pattern Baldness in Turkish Male Population Aged 50 Years and Older

Background/Objectives: Male pattern baldness (MPB) is a complex polygenic trait influenced by genetic and non-genetic factors, with susceptibility loci on both autosomal and X chromosomes. This study aimed to develop an exploratory genetic model for distinguishing no baldness (Hamilton–Norwood [HN] grade 1) from severe baldness (HN grades 5–7) in Turkish men aged 50 years and older. Methods: Buccal-swab samples from 144 unrelated male volunteers (30 HN grade 1 and 114 HN grades 5–7) were genotyped using a multiplex SNaPshot assay containing 23 SNPs selected from previously reported MPB-associated loci. Participants were divided into a training group (n = 86; 18 HN grade 1 and 68 HN grades 5–7) and a held-out test group derived from the same cohort (n = 58; 12 HN grade 1 and 46 HN grades 5–7). Binary logistic regression was used for model development. The held-out test group was not used for SNP selection or model choice. Discrimination was assessed using receiver operating characteristic analysis and fivefold cross-validation; calibration of the final model was additionally evaluated using the Brier score and calibration intercept and slope. Results: The final 9-SNP model yielded AUCs of 0.879 and 0.777 in the training and held-out test groups, respectively. Fivefold cross-validation produced an overall AUC of 0.786 (bootstrap 95% CI, 0.696–0.868). At the conventional threshold of 0.50, test sensitivity and specificity were 0.935 and 0.250, whereas the optimized threshold of 0.843 yielded 0.717 sensitivity and 0.750 specificity. In the held-out test group, the Brier score was 0.159, the calibration intercept was 0.568, and the calibration slope was 0.492, indicating residual overfitting despite close agreement between mean predicted and observed event frequency. Among the retained markers, rs7349332 in WNT10A was the only statistically significant predictor in the multivariable model. Conclusions: The 9-SNP model showed moderate discriminatory performance for severe MPB in this Turkish cohort but should be considered a candidate, proof-of-concept model. The limited and imbalanced sample, extreme-phenotype design, internal rather than external validation, and exclusion of intermediate HN grades restrict generalizability; external validation in larger independent cohorts is required before forensic implementation.