Document Detail

Prenatal diagnosis of minute supernumerary marker chromosomes.
MedLine Citation:
PMID:  15689640     Owner:  NLM     Status:  MEDLINE    
The identification of supernumerary marker chromosomes (SMC) at prenatal diagnosis is problematic, particularly for the prediction of phenotype. The assessment of phenotypic risk is based on the size, morphology and origin of the SMC. Fluorescence in situ hybridization (FISH) characterization and family studies are also employed to aid in determining the significance of a prenatally ascertained SMC. Generally, SMC containing euchromatin are more likely to be associated with abnormal phenotypes and SMC without euchromatin are more likely to result in normal phenotypes. The smallest of SMC, minute SMC (minSMC) appear as dot-like or centric fragments and are particularly difficult to identify and characterize. Previous empirical observations suggested that the risk of phenotypic abnormality in prenatally ascertained minSMC was < or = 5%. We identified minSMC in chorionic villus samples (CVS) or amniocytes from 11 unrelated pregnancies. The chromosomal origin of each minSMC was identified by sequential FISH analysis with chromosome-specific centromere probes. Further FISH analysis with whole chromosome paint probes was undertaken to assess each minSMC for the presence or absence of euchromatin, since the presence of euchromatin may be associated with a higher risk of abnormality. Two minSMC were shown to have euchromatin. The first, a minSMC(12) was found in CVS but not confirmed in amniocytes, indicating confined placental mosaicism. The second, a minSMC derived from chromosome 19, was associated with ultrasound abnormalities. Apart from a case with mild speech delay, the remaining minSMC cases without detectable euchromatin had a normal outcome at birth and/or on longer term follow-up. Additional FISH analyses with a telomeric repeat probe showed no signal on any of the minSMC tested, suggesting that they were ring chromosomes in structure. These data further support the concept that minSMC containing euchromatin are more likely to be associated with an abnormal phenotype, although as more data are collected, this may vary by chromosome of origin. The absence of detectable euchromatin, while not guaranteeing a normal result, is most likely to have a normal outcome. The present report and previous studies do not yet allow any significant adjustment of the empirical < or = 5% risk estimate for minSMC identified at prenatal diagnosis. However, reporting of additional cases with characterization of the minSMC and particularly with long-term follow-up will, in time, allow for more accurate risk estimates and provide prognostic information.
Philip D Cotter; Kathryn Drexler; Amy L Corley; Susan M Covert; Jessica S Moland; Inna J Govberg; Mary E Norton
Publication Detail:
Type:  Case Reports; Journal Article     Date:  2005-01-24
Journal Detail:
Title:  Gynecologic and obstetric investigation     Volume:  60     ISSN:  0378-7346     ISO Abbreviation:  Gynecol. Obstet. Invest.     Publication Date:  2005  
Date Detail:
Created Date:  2005-07-27     Completed Date:  2005-11-01     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  7900587     Medline TA:  Gynecol Obstet Invest     Country:  Switzerland    
Other Details:
Languages:  eng     Pagination:  27-38     Citation Subset:  IM    
Copyright Information:
Copyright 2005 S. Karger AG, Basel.
Department of Pathology and Division of Medical Genetics, Children's Hospital Oakland, Oakland, CA 94609, USA.
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MeSH Terms
Chorionic Villi Sampling*
Chromosome Aberrations*
Chromosome Disorders / diagnosis*,  genetics
Fetal Diseases / diagnosis*
In Situ Hybridization, Fluorescence
Middle Aged
Predictive Value of Tests

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