Comparison of 2D:4D digit ratios in patients with Hashimoto's and Graves' diseases: A systematic review

This systematic review includes three descriptive studies that investigated the relationship between biological markers such as the 2D:4D digit ratio and morphological femininity and thyroid diseases. Two of the studies involved only female participants, while one included both males and females. Participants ranged in age from 20 to 80, and all studies applied inclusion criteria such as being of the same ethnic origin and having no history of hand or finger injuries. The studies suggest that autoimmune thyroid disorders like Hashimotos thyroiditis and Graves' disease may be associated with prenatal exposure to sex hormones. A higher 2D:4D ratio is considered indicative of greater prenatal estrogen exposure, whereas a lower ratio reflects higher testosterone exposure. Individuals with Hashimoto's thyroiditis were found to have significantly higher 2D:4D ratios compared to healthy controls, while those with Graves' disease had lower ratios. Differences in the right-hand 2D:4D ratio were more pronounced than those in the left hand. One study also found a positive correlation between morphological femininity and the severity of Hashimoto's disease, as measured by TPOAb levels. These findings indicate that hormonal influences during prenatal and adolescent periods may have lasting effects on the immune system and thyroid function. However, all studies included in this review are descriptive in nature, and thus, the results are correlational rather than causal. Further prospective studies and systematic reviews are needed to better understand these associations.