Table 1The OMIM numbering system

MIM number rangeaExplanation
100000-199999Autosomal loci or phenotypes (entries created before May 15, 1994)
200000-299999Autosomal loci or phenotypes (entries created before May 15, 1994)
300000-399999X-linked loci or phenotypes
400000-499999Y-linked loci or phenotypes
500000-599999Mitochondrial loci or phenotypes
600000-Autosomal loci or phenotypes (entries created after May 15, 1994)

MIM numbers are frequently preceded by a symbol. An asterisk (*) before a MIM number indicates that the entry describes a distinct gene or phenotype and that the mode of inheritance of the phenotype has been proved (in the judgment of the authors and editors) and that the phenotype described is not known to be determined by a gene represented by other asterisked entries in MIM.

A number sign (#) before a MIM number describing a phenotype indicates that the phenotype is caused by mutation in a gene represented by another entry and usually in any of two or more genes represented by other entries. The number sign is also used for phenotypes that result from specific chromosomal aberrations, such as Down syndrome, and for contiguous gene syndromes, such as Langer-Giedion syndrome. Whenever a number sign is used, the reason is stated at the outset of the entry.

The absence of an asterisk (or other sign) preceding the number indicates that the distinctness of the phenotype as a mendelizing entity or the characterization of the gene in the human is not established.

From: Chapter 7, Online Mendelian Inheritance in Man (OMIM): A Directory of Human Genes and Genetic Disorders

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