Difficulty in LW typing as revealed by a family study

A family is described in which two members of the second generation are of the phenotype LW3. In the course of the investigation the mother of the LW3 propositus was at first believed to be phenotypically LW3 as well. Eventually, it was shown that she is, in fact, phenotypically LW2 but that her R-1 (no D), LWlw, genotype had resulted in less LW being present on her red blood cells than is expected in LW2 persons. This reduced level of LW could not be detected with one example of anti-LW made by an LW3 individual.