OMIM can be searched from its homepage or from any page in the NCBI Entrez suite of databases. Information in OMIM can be retrieved by queries on MIM number, disorder, gene name and/or symbol, or plain English (e.g. ‘cryptorchidism webbed neck’). The limits function may be used to perform a restricted search of parts of a MIM entry (number, titles, references, etc.) and/or type of MIM entry (gene or phenotype). Regardless of the method used, the search engine ranks the entries that match the query so that the entries that are most relevant to the question are generally in the top 10 retrievals.
Each OMIM entry is assigned a unique six-digit number whose first digit indicates whether its inheritance is autosomal, X-linked, Y-linked or mitochondrial: 1, autosomal loci or phenotypes (entries created before May 15, 1994); 2, autosomal loci or phenotypes (entries created before May 15, 1994); 3, X-linked loci or phenotypes; 4, Y-linked loci or phenotypes; 5, mitochondrial loci or phenotypes; and 6, autosomal loci or phenotypes (created after May 15, 1994).
In addition, MIM entries are categorized by whether they contain information on genes, phenotypes or both. This is denoted by the symbol that precedes a MIM number. An asterisk (*
) before an entry number indicates a gene of known sequence. A number symbol (#) before an entry number indicates that it is a descriptive entry, usually of a phenotype, and does not represent a unique locus. The reason for the use of the #-sign is given in the first paragraph of the entry. Discussion of any gene(s) related to the phenotype resides in appropriate entry(ies) as described in the first paragraph. A plus sign (+) before an entry number indicates that the entry contains the description of a gene of known sequence and a phenotype. A percentage sign (%) before an entry number indicates that the entry describes a confirmed Mendelian phenotype or phenotypic locus for which the underlying molecular basis is not known. No symbol before an entry number generally indicates a description of a phenotype for which the Mendelian basis, although suspected, has not been clearly established or that the distinctness of this phenotype from that in another entry is unclear. A caret symbol (^) before an entry number means the entry was removed from the database or moved to another entry as indicated. As of September 13, 2004, OMIM had 10
208 entries describing genes with known sequence and 5777 entries describing phenotypes (Table ).
Number of gene and phenotype entries in OMIM as on September 13, 2004