I have a very basic biology question. I am reading the description of gene FAM166A here, and I have no idea what "sequence similarity 166" means. What does 166 stand for, what is this gene's sequence "similar to"? And what does member A mean?

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    $\begingroup$ Family membership is probably referring to something similar to this: ebi.ac.uk/training/online/course/…. I'm not sure how the sequence similarity is scored, though. $\endgroup$
    – CKM
    Jul 25, 2018 at 19:02
  • $\begingroup$ Oh okay, then this gene named FAM166A is member A of the protein family with ID 166 where each family is determined based on sequence similarity. Thanks! $\endgroup$
    – user5054
    Jul 25, 2018 at 19:10

1 Answer 1


The FAM symbols are defined in the HUGO Gene Nomenclature Committee guidelines.

The FAM symbol is an anonymous and temporary identifier that is given to groups of poorly characterised genes which share more than 40% amino acid sequence identity (see Section 4.1).

There are two human genes/proteins in the sequence similarity 166 group; FAM166A and FAM166B. These have some sequence similarity (more than 40%) but function of this similar sequence is currently unknown. Once further characterisation has been performed for any FAM group they will likely receive more meaningful names.


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