MTHFR and hematocrit: Results: Children and adolescents with HT presented approximately 2.5 times more frequently the T allele sequences (CT and TT variants) and the T alleles in total for the 677C>T polymorphism of the MTHFR gene compared to the healthy population (OR: 2.56, CI: 1.53–4.21 and OR: 2.57, CI: 1.59–4.16, respectively).