TTR (transthyretin)

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Human Uniqueness Compared to "Great Apes": 
Likely Difference
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Transthyretin (TTR) is a protein made in the liver and the choroid plexus of the brain, resulting in its presence in the blood plasma and cerebrospinal blood respectively. It the principal thyroid hormone transport protein in cerebrospinal fluid and is responsible for delivering the hormone to the brain. Expression levels in humans compared with "great apes" appear to be increased both in circulating blood and in cerebrospinal blood, and this is presumed to be due to increased gene expression at the sites of synthesis mentioned. There may be some connection to apparent differences in thyroid hormone metabolism between humans and chimpanzees. The biological significance of this event is unknown. One comparative study between humans and chimpanzees suggested that TTR has has undergone recent positive selection in humans. Notably transthyretin is also the carrier for retinol binding protein, which keeps retinol in the circulation.

Type of Human-Specific Changes in TTR
Tissue Expression Pattern Change



Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Definite Appearance: 
100 thousand years ago
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Topic Certainty
Thyroid Hormone Metabolism Likely
Genetics Topic Attributes
Gene symbols follow the HUGO Gene Nomenclature Committee standard.
Gene Symbol Type of Human-Specific Changes
TTR Expression Pattern Change


  1. Interspecies subtractive hybridization of cDNA from human and chimpanzee brains., Nadezhdin, E V., Vinogradova T V., and Sverdlov E D. , Dokl Biochem Biophys, 2001 Nov-Dec, Volume 381, p.415-8, (2001)
  2. Proteomic comparison of human and great ape blood plasma reveals conserved glycosylation and differences in thyroid hormone metabolism., Gagneux, P, Amess B, Diaz S, Moore S, Patel T, Dillmann W, Parekh R, and Varki Ajit , Am J Phys Anthropol, 2001 Jun, Volume 115, Issue 2, p.99-109, (2001)