Camurdan et al., observed higher rates of vitamin D deficiency (25(OH)D level < 37.5 nmol/L; 73.1% vs. 17.6%; p < 0.0001) and lower 25(OH)D levels (31.2 vs. 57.9 nmol/L; p < 0.001) in 78 children with recently diagnosed HT compared with 74 controls, and an inverse correlation between 25(OH)D and anti-TPO levels (r = −0.30; p = 0.007) [32]. The gene discussed is TPO; the disease is hematocrit.