[The Lewis blood group is more frequently nonexpressed in psychiatry than in the general population]

The Lewis-negative blood group seems to occur more frequently in psychiatry than in the overall population. The Lewis group is not genetically determined at birth as Lewis-positive or negative; the latter occurs significantly more often among 219 "overall" psychiatric patients than in the overall population: 47% instead of 10%. As a first approximation, the absence of transition from its negativity to positivity seems to constitute a favoring factor for the subsequent clinical development of a psychiatric syndrome, without allowing to predict its nature or severity. For the other blood groups, the genetic determination of which is irreversible, the same sample shows the same repartition as in the overall population.