Null allele in a human polymorphism restricted to the placenta: call for a search.

The identification of a null allele in a human genetic system restricted to the placenta is a great challenge for two reasons: the impossibility of carrying out family studies and the unviability of sample recollections because the placenta itself is a disposable universe. Thus, in addition to reporting the finding of a null phenotype of placental alkaline phosphatase in a dark mulatto newborn from a black mixed population of Bahia, Brazil, here we present other evidence for the presence of the ALPP*Q0 allele with considerably high frequency in this population.