The genes surrounding APOE on chromosome 19 can amplify or moderate the risk your APOE status already confers.
Neighboring genes share regulatory regions with APOE and are often inherited together with it, which makes their effects hard to separate from APOE's own.
The Biology
Neighboring genes often share regulatory regions and are inherited together. The stretch of chromosome 19 around APOE contains variants studied for effects on Alzheimer's and cardiovascular risk. TOMM40 encodes a mitochondrial outer membrane translocase that imports proteins into mitochondria, a function with possible relevance to neurodegeneration.
What Varia Analyzes
TOMM40 (rs2075650) sits next to APOE and is in strong linkage disequilibrium with APOE e4: its G allele travels with e4. TOMM40 has been studied as an Alzheimer's age-of-onset modifier (Roses et al., 2010), but a replication study did not confirm the reported age-of-onset association (Cruchaga et al., 2011), and the catalog treats the rs2075650 association as largely reflecting APOE e4 rather than a separate TOMM40 effect. The APOC1 H2 haplotype, which works through a different mechanism, has its own page in Domain XII.
Why It Matters
Because TOMM40 and APOE are inherited together so often, a TOMM40 result mostly restates what the APOE result already shows. Varia reports it with that caveat rather than as an independent signal.