The great apes include, in addition to Homo, the genera Pongo (orangutans), Gorilla (gorillas), and Pan, the latter comprising two species, P. troglodytes (chimpanzees) and P. paniscus (bonobos). Adult-onset
hypothyroidism was previously reported in 4 individual nonhuman great apes. However, there is scarce information on normal serum
thyroid hormone levels and virtually no data for thyroid
autoantibodies in these animals. Therefore, we examined
thyroid hormone levels and TSH in all nonhuman great ape genera including adults, adolescents, and infants. Because
hypothyroidism in humans is commonly the end result of thyroid autoimmunity, we also tested healthy and hypothyroid nonhuman great apes for
antibodies to
thyroglobulin (Tg),
thyroid peroxidase (TPO), and the
TSH receptor (TSHR). We established a
thyroid hormone and TSH database in orangutans, gorillas, chimpanzees, and bonobos (447 individuals). The most striking differences are the greatly reduced free-T4 and free-T3 levels in orangutans and gorillas vs chimpanzees and bonobos, and conversely, elevated TSH levels in gorillas vs Pan species.
Antibodies to Tg and TPO were detected in only 2.6% of adult animals vs approximately 10% in humans. No animals with Tg, TPO, or TSHR
antibodies exhibited thyroid dysfunction. Conversely, hypothyroid nonhuman great apes lacked thyroid
autoantibodies. Moreover, thyroid histology in necropsy tissues was similar in euthyroid and hypothyroid individuals, and lymphocytic infiltration was absent in 2 hypothyroid animals. In conclusion, free T4 and free T3 are lower in orangutans and gorillas vs chimpanzees and bonobos, the closest living human relatives. Moreover, thyroid
autoantibodies are rare and
hypothyroidism is unrelated to thyroid autoimmunity in nonhuman great apes.