MCA/MR syndrome in a female infant with tetraploidy mosaicism: review of the human polyploid phenotype.

We report on a 3-month-old girl with unusual facial appearance, short neck with low posterior hairline, wide chest, valvular pulmonic stenosis, abnormal fingernails, and diploid-tetraploid mosaicism (46,XX/92,XXXX in 7.2% of peripheral leucocytes and in 29% of skin fibroblasts). Comparison with 11 previously reported cases with mosaic or complete tetraploidy does not establish an easily recognizable syndrome. However, a malformation pattern is apparent when tetraploidy patients are compared with 14 cases of triploid mosaicism and 44 previously reported cases of nonmosaic triploidy. A history of sex hormone exposure was present in 5 of 11 pregnancies resulting in tetraploidy; this exposure may correlate with the occurrence of tetraploidy in polycystic ovary syndrome and in tumors of the female reproductive tract. The mechanism of dysmorphogenesis involved in polyploidy is considered, including hypotheses of altered nuclear/cytoplasmic ratio, of trophoblastic alteration, of delayed cell division, or of altered autosome/active X chromosome ratio.