Inv(4)(p16q21). A five-generation pedigree with 24 carriers and no recombinants.

A familial inv(4)(p16q21) ascertained through a woman who had a thanatophoric dwarf daughter and two abortions is presented. She and 23 other relatives were carriers, but no recombinants were found. The proportion of abortions and neonatal deaths in carriers' offspring was similar to that in non-carriers. A random segregation of the inverted chromosome was observed. The analysis of the present and previous familial chromosome 4 pericentric inversions indicates that: the breakpoint in q, with a limit between q21 and q25 determines the occurrence of inherited unbalances, and most recombinant chromosomes have duplication of the larger distal segment.