RESUMO
The phenotypic spectrum of 46,XX/46,XY chimeric patients is variable. It ranges from normal male or female genitalia to different degrees of ambiguous genitalia. Chimerism results from the amalgamation of two different zygotes in a single embryo, whereas mosaicism results from a mitotic error in a single zygote. Several other mechanisms resulting in a chimera have been discussed in the literature. Here, we report on a new case of chimerism (46,XX/46,XY) diagnosed at 17 weeks' gestation on amniocentesis performed because of advanced maternal age. Ultrasound examination revealed normal female external genitalia, and a healthy baby girl was delivered at term. We used polymorphic markers spanning the X chromosome and several autosomes in order to identify the genetic mechanism involved. Mosaicism was excluded because of the presence of 3 alleles at 11 autosomal and 4 X chromosome loci. On autosomes, the origin of this third allele was maternal for two pericentromeric markers (located on 2p11.2 band and 8p11.2 band), paternal for six markers and paternal or maternal for the other three markers. On the X chromosome, the origin of the third allele was maternal for all four markers. Thus, two different paternal and maternal haploid sets were observed. These results are compatible with a tetragametic chimera.
Assuntos
Cromossomos Humanos X , Cromossomos Humanos Y , Diagnóstico Pré-Natal , Alelos , Amniocentese , Feminino , Genótipo , Haploidia , Humanos , Recém-Nascido , Cariotipagem , Idade Materna , Fenótipo , Polimorfismo Genético , Resultado do TratamentoRESUMO
We have analyzed 40 cases of human XX male or XX true hermaphrodites negative for Y DNA sequences including ZFY. Among these patients we were able to demonstrate the existence of at least 3 mechanisms. 1) In one case a mosaïscism 46XY/46XX is limited to the gonad and only detected by PCR. 2) Familial cases compatible with the mutation of an autosomal (or pseudo-autosomal) down stream sex determining gene. 3) We finally observed 5 cases lacking ZFY meanwhile carrying Y specific sequences near to the pseudo-autosomal boundary, redifining the region where TDF must lie.
