Permanent tooth sizes in 46,XX-males.

Measurements of permanent tooth sizes in four XX-males showed their teeth to be smaller than those of male controls and similar in size to those of female controls. The teeth of the XX-males were smaller than those of their first-degree male relatives and of the same size as those of three of their mothers. The teeth of three fathers of XX-males were similar in size to control males and the teeth of three mothers of XX-males were similar in size to control females. The detailed knowledge that exists regarding the sequence and timing of tooth crown development allows the following implications to be made from our results. Growth retardation in XX-males is of primary genetic origin and is due to the absence of the gene(s) normally located on the Y-chromosome. Growth retardation, compared to normal males, is apparent and final three years after birth, conceivably begins after 2--3 months of foetal life and persists during childhood. It is unlikely that XX-males have had a Y-chromosome at any stage. If maleness is caused by a recessively inherited translocation or a mutational acquisition of the testis-determining gene(s), the genes influencing growth are not involved in either mechanism.