ABSTRACT: We present the case of a monozygotic twin pregnancy discordant for phenotype and karyotype. A chorionic villus sample was performed at the 11th week of gestation in a primigravida because of cystic hygroma detected by ultrasound in one twin of a monochorionic, biamniotic pregnancy. Rapid testing by means of quantitative fluorescence polymerase chain reaction and conventional karyotyping, obtained by both short- and long-term culture, revealed a homogeneous monosomy X (45,X). Amniocentesis was performed separately for both twins before termination and showed an homogeneous monosomy X in one sample and a 46,X,del(X)(p11.1) karyotype in the other one. Postmortem fetal tissues culture confirmed the discordant karyotype between the two embryos. Placental samples obtained after termination revealed the cell line which was not detected at chorionic villus sampling. Based on this and previous reports, we suggest that in cases of a phenotypic discordance detected at ultrasound in the first trimester, it is advisable to perform a karyotype analysis on amniocytes because it better reflects fetal constitution rather than chorionic villi or lymphocytes in case of heterokaryotipic monosomy X monochorionic twins.
Twin Research and Human Genetics 07/2008; 11(3):352-6. · 1.70 Impact Factor
Prenatal Diagnosis 01/2007; 26(12):1186-9. · 2.11 Impact Factor
ABSTRACT: We evaluated the experiences of 19 Italian laboratories concerning 241 small supernumerary marker chromosomes (sSMCs) with the aim of answering questions arising from their origin from any chromosome, their variable size and genetic content, and their impact on the carrier's phenotype.
Conventional protocols were used to set up the cultures and chromosome preparations. Both commercial and homemade probes were used for the fluorescent in situ hybridization analyses.
A total of 113 of the 241 sSMCs were detected antenatally, and 128 were detected postnatally. There were 52 inherited and 172 de novo cases. Abnormal phenotype was present in 137 cases (57%), 38 of which were antenatally diagnosed. A mosaic condition was observed in 87 cases (36%). In terms of morphology, monocentric and dicentric bisatellited marker chromosomes were the most common, followed by monocentric rings and short-arm isochromosomes. The chromosomes generating the sSMCs were acrocentric in 132 cases (69%) and non-acrocentric chromosomes in 60 cases (31%); a neocentromere was hypothesized in three cases involving chromosomes 6, 8, and 15.
The presented and published data still do not allow any definite conclusions to be drawn concerning karyotype-phenotype correlations. Only concerted efforts to characterize molecularly the sSMCs associated or not with a clinical phenotype can yield results suitable for addressing karyotype-phenotype correlations in support of genetic counseling.
Genetics in Medicine 03/2005; 7(9):620-5. · 4.76 Impact Factor