||common in clinvar
||Hyperlipoproteinemia, type III
rs121918394 represents a variant in the APOE gene on chromosome 19. There are two known alternative alleles, known as c.490A>C, p.Lys164Gln or K164Q, or as c.490A>G, p.Lys164Glu or K164E, using current reference numbering. However, in older publications, this position is historically described as being amino acid 146 (not 164), and so p.Lys146Gln and p.Lys146Glu can also be found as aliases in the literature.
The K164E/K146E variant has been designated ApoE1-Harrisburg according to OMIM, and is a dominant mutation leading to familial dysbetalipoproteinemia. This variant is called i6007512 by 23andMe.
The K164Q/K146Q variant is also a dominant mutation leading with high penetrance to type III hyperlipoproteinemia (i.e. familial dysbetalipoproteinemia), according to OMIM, but it is reportedly observed (electrophoretically) as an E2 phenotype.
Note that the first ApoE1 allele described derives from rs267606664, a variant at a different amino acid, known as c.434G>A, p.Gly145Asp or G145D, or in older numbering, p.Gly127Asp or G127D.