diseases are often thought of as the result of a single "disease"
allele, in contrast to a single "normal" allele. In
fact, most human gene loci are highly polymorphic, and there are
large numbers of variant alleles for medical conditions of
interest. An even greater range of variation remains
undetected, because most nucleotide substitutions (especially
third-position changes) do not noticeably affect gene activity.
Genetically-influenced traits in humans were first listed in
1966 in book form, Mendelian Inheritance in Man, which
grew from a slender single volume to a bulky two-volume 12th
edition in 1998 before it went entirely online as OMIM in 2004. Early
editions concerned phenotypically observable traits; the latest
editions make use of information in the Human Genome Project
and are strongly molecularly based.
In 2007, OMIM
allelic variants at the Phenylalanine Hydroxylase (PAH) locus
in the tables below.
base => premature termination
In the table below, XXX###YYY describes a mis-sense substitution of amino acid XXX to YYY at position ###;
XXX###TER describes a termination (nonsense) at position ###
IVS refers to an alteration at an intervening spacer (intron)