As referred to earlier, a numbering system has also come into extensive use in connection with disorders that are identical or nearly identical but that are due to mutations in separate genes. In the past decade or so, OMIM has made increasing use of numerical or alphabetic systems for phenotypic series (e.g., DFNB#- for the many [>68] forms of autosomal recessive nonsyndromic deafness, LQT#- for the many [>7] forms of long QT syndrome, and SPG#- for the many [gt;33] forms of spastic paraplegia). Historically, the precedent for numbering phenotypicwhi series was established with the glycogen-storage diseases, the mucopolysaccharidoses, and the Ehlers-Danlos syndromes. Confusion can arise when workers use different numbers for the same disorder (e.g., see the complementation groups of peroxisomal disorders [MIM +170993ff]) or if the phenotype was not fully characterized before being entered into the series.