Selection of particular mutations of a given gene for inclusion as AVs in OMIM has been based on general criteria, including the following: (1) the first or first few disease-related mutations to be identified in the given gene; (2) any mutation with a particularly high frequency, such as Phe508del in the CFTR gene (MIM *602421.0001) in cystic fibrosis (MIM #219700); (3) a mutation related to a distinct phenotype not previously represented in the list; (4) mutations of historical interest, such as the specific mutation in the family or population in which the phenotype was first described—for example, the mutation in the CLCN1 gene (MIM *118425.0006) in the family of Dr. Thomsen, who first described Thomsen disease (MIM #160800); (5) any mutation with a peculiar ethnic or geographic distribution; (6) any mutation arising through a distinctive mutagenic mechanism such as gene conversion (as in classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency [MIM *201910.0001]) or gene fusion (as in Hb Lepore [MIM +142000.0019ff]); (7) any mutation producing the phenotype through a distinctive pathogenetic mechanism; (8) mutations associated with autosomal dominant versus autosomal recessive inheritance with different mutations in the same gene, as in therecessive (MIM *139250.0005) and dominant (MIM *139250.0007) forms of isolated growth hormone deficiency due to allelic mutations in the growth hormone gene (GH1); and (9) polymorphisms demonstrating association with disease—for example, the Y402H polymorphism of complement factor H (CFH [MIM *134370.0008]) in age-related macular degeneration (MIM #603075). The last category represents so-called susceptibility genes, as discussed later. Most are part of the multifactorial basis of common disorders.