THCV is different from THC (and other well known cannabinoids, like CBD, CBC, CBN etc.) in the sense that it does not actually come from CBGA.
The cannabis plant combines geranyl pyrophosphate 

THCV is different from THC (and other well known cannabinoids, like CBD, CBC, CBN etc.) in the sense that it does not actually come from CBGA. 
The cannabis plant combines geranyl pyrophosphate with olivetolic acid to create CBGA, from there all the other cannabinoid acids/cannabinoids are created.

Enzymes in the plant convert CBGA to THCA, CBDA and CBCA, which then convert to their neutral counterparts THC, CBD or CBC (which can then degrade to other cannabinoids like CBN and CBL).
To create THCV the difference begins before the creation of any cannabinoids. Instead of combining geranyl pyrophosphate with olivetolic acid to create CBGA, THCV comes from a process which begins by combining geranyl pyrophosphate with divarinolic acid to create CBGVA. Like with CBGA, CBGVA converts through enzymes in the plant to create the "varin" versions of all the other cannabinoids.
In the case of THCV, CBGVA converts to THCVA by the THC synthase enzyme (like wise the CBD synthase will convert CBGVA to CBDVA). Decarboxylation then converts the THCVA to THCV (just as it would convert the CBDVA to CBDV).
THCV is generally more common among south and western African strains of cannabis, though Pakistan, India and China have all produced strains high in THCVA/THCV.
THCV is also psychoactive, though much less so than THC and requires higher doses for such effects than is required of THC. The psychoactive effects also dissipate much faster with THCV.
Though many of its effects are considered dose dependant, THCV can block the CB1 receptors while activating the CB2 receptors. This combination has led to interest in many applications, with the CB1 blocking effect considered significant for appetite suppression.

THCV is being investigated for its potential as a treatment for diabetes, and has also demonstrated anti epileptic and anti convulsive properties. One of the main areas of investigation is neuropathic pain and inflammation.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2931567/?tool=pubmed

GW Pharmaceuticals are currently conducting a phase 1 trial to investigate THCV for type 2 diabetes.
http://www.gwpharm.com/Metabolic%20Disorders.aspx