Minus-minus blood group phenotypes are characterized by the absence of any detectable phenotypic representation of the alleles expected at the determining gene loci. Double minus phenotypes have been found in most blood group systems but all individuals thus far tested for the Lutheran factors have been Lu(a+b+), Lu(a+b+) or Lu(a−+). Six individuals with the hitherto undisclosed blood group Lu(a−b−) were found in three generations of a Caucasian family.

Unlike the other minus-minus phenotypes, to which recessive genetical backgrounds have been assigned, Lu(a−b−) appears to be a dominant character.

The Kidd groups of the family are also anomalous: The proposita and her two brothers are Lu(a−b−), Jk(a+b−) yet their father is Lu(a−b−), Jk(a−b+) and their mother is Lu(a−b+), Jk(a+b−). Possible genetical backgrounds are discussed.