Gongjie Zhang,1 Xinlyu Huang,1 Hanlin Li,1 Huizi Gong,1 Yabin Zhou,2 Fang Liu1 

1Department of Dermatology, Venereology and Cosmetology, Beijing Chaoyang Hospital, Capital Medical University, Beijing, 100020, People’s Republic of China; 2Department of Dermatology, Beijing Children’s Hospital, Capital Medical University, National Centre for Children’s Health, Beijing, 100045, People’s Republic of China

Correspondence: Yabin Zhou, Department of Dermatology, Beijing Children’s Hospital, Capital Medical University, National Centre for Children’s Health, No. 56 Nan Lishi Road, Xicheng District, Beijing, 100045, People’s Republic of China, Tel +86 10 59616884, Email chouyabin@163.com Fang Liu, Department of Dermatology, Venereology and Cosmetology, Beijing Chaoyang Hospital, Capital Medical University, No. 8 Gongti Nan Road, Chaoyang District, Beijing, 100020, People’s Republic of China, Tel +86 18611369216, Email roseliufang@qq.com

Background: Hair loss is common in hypothyroidism patients. However, the link with alopecia areata (AA) and androgenetic alopecia (AGA) is unclear. Previous observational studies have presented completely opposite results. This study aims to causally link hypothyroidism with AA and AGA.
Methods: A two-sample Mendelian Randomization (MR) study, utilizing data from FinnGen Consortium, investigated the causal link between hypothyroidism and AA and AGA. We employed Inverse Variance Weighted (IVW), MR-Egger, Weighted Median, Simple Mode, and Weighted Mode to assess the risk association.
Results: The discovery samples included 13,429 hypothyroidism cases (94,436 controls), 767 alopecia areata cases (394,105 controls), and 220 androgenetic alopecia cases (219,249 controls). MR analysis showed a causal link between hypothyroidism and AA, with significant results from IVW (OR, 1.34; CI, 1.16– 1.56; P = 0.0001), MR-Egger (OR, 1.56; CI, 1.09– 2.23; P = 0.0240), and weighted median (OR, 1.34; CI, 1.06– 1.69; P = 0.0140). However, no clear causal relationship was found between genetically predicted hypothyroidism and AGA risk (p > 0.05).
Conclusion: The results show hypothyroidism causally associated with AA onset, but not AGA. These findings address contentious issues in observational studies. Comprehensive thyroid function assessments are crucial for AA patients, emphasizing thorough clinical examinations’ importance.

Keywords: hypothyroidism, alopecia areata, androgenetic alopecia, Mendelian randomization study, causality