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Monday 17 October 2005

locus; loci; genetic locus


Definition: A locus is the position of a gene on a chromosome or other chromosome markers; also, the DNA at that position.

Originally, locus symbols (e.g., DYT1 ) were introduced to specify chromosomal regions that had been linked to a familial disorder with a yet unknown gene.

Symbols were systematically assigned in a numerical series to designate mapped loci for a specific phenotype or group of phenotypes.

Since the system of designating and using locus symbols was originally established, both our knowledge and our techniques of gene discovery have evolved substantially.

The current system has problems that are sources of confusion, perpetuate misinformation, and misrepresent the system as a useful reference tool for a list of inherited disorders of a particular phenotypic class.

These include erroneously assigned loci, duplicated loci, missing symbols, missing loci, unconfirmed loci in a consecutively numbered system, combining causative genes and risk factor genes in the same list, and discordance between phenotype and list assignment.

The system could be significantly improved by creating distinct lists for clinical and research purposes, creating more informative locus symbols, distinguishing disease-causing mutations from risk factors, raising the threshold of evidence prior to assigning a locus symbol, paying strict attention to the predominant phenotype when assigning symbols lists, and having a formal system for reviewing and continually revising the list that includes input from both clinical and genetics experts.

See also

- morbid locus

Open references

- Fixing the broken system of genetic locus symbols: Parkinson disease and dystonia as examples. Marras C, Lohmann K, Lang A, Klein C. Neurology. 2012 Mar 27;78(13):1016-24. doi : 10.1212/WNL.0b013e31824d58ab PMID: 22454269 Free