Prenatal identification of small mosaic markers of different chromosomal origins

Supernumerary minute ring chromosome 14 in a man with primary infertility and left varicocele

OBJECTIVE

To describe a case of supernumerary minute ring chromosome (SMRC) in an infertile man, with the concurrent finding of a left varicocele.

DESIGN

Case report.

SETTING

Urologic infertility clinic in a university hospital.

PATIENT(S)

Male patient presenting with primary infertility.

INTERVENTION(S)

Karyotyping, genetic counseling, and microsurgical left varicocelectomy.

MAIN OUTCOME MEASURE(S)

Sperm concentration and motility, chromosomal number and structure.

RESULT(S)

Fluorescence in situ hybridization revealing SMRC 14. Sperm concentration and motility improved after left varicocele repair.

CONCLUSION(S)

A karyotype should be included in the evaluation of severe oligospermia. Although SMRC 14 may be associated with fertility problems, repair of a coexisting varicocele should be considered in these patients.

Small supernumerary marker chromosomes – progress towards a genotype-phenotype correlation

Small supernumerary marker chromosomes (sSMC) are still a major problem in clinical cytogenetics as they are too small to be characterized for their chromosomal origin by traditional banding techniques, but require molecular cytogenetic techniques for their identification. Apart from the correlation of about one third of the sSMC cases with a specific clinical picture, i.e. the i(18p), der(22), i(12p) (Pallister Killian syndrome) and inv dup(22) (cat-eye) syndromes, most of the remaining sSMC have not yet been correlated with clinical syndromes. Recently, we reviewed the available >1600 sSMC cases (Liehr T, sSMC homepage: http://mti-n.mti.uni-jena.de/~huwww/MOL_ZYTO/sSMC.htm). A total of 387 cases (including the 45 new cases reported here) have been molecularly cytogenetically characterized with regard to their chromosomal origin, the presence of euchromatin, heterochromatin and satellite material. Based on analysis of these cases we present the first draft of a basic genotype-phenotype correlation for sSMC for all human chromosomes apart from the chromosomes Y, 10, 11 and 13.

The identification of small supernumerary marker chromosomes; the experiences of 15,792 fetal karyotyping from Turkey

Small supernumerary marker chromosomes (sSMCs) are often associated with developmental abnormalities and malformations are de novo in approximately 60% of the cases. Fluorescence in situ hybridization (FISH) techniques using various probes provided the possibility to analyze and characterize sSMCs, which is highly important for prenatal diagnosis and genetic counseling. We now present the establishment of a specific strategy to identify the origin and structure of the sSMCs using a combination of conventional banding and classical FISH techniques. Based on this strategy, in a series of 15,792 prenatal karyotypes, 20 cases with sSMCs (prevalence 1.26 per 1000) were diagnosed. Eighteen of these cases were completely analyzed by FISH using commercial probes and Chromoprobe Multiprobe-I System. Out of 20 sSMCs 12 were satellited (10 bisatellited and two monosatellited) (60%) and eight were non-satellited (six ring-like and two isochromosomes) (40%). sSMCs were mostly derived from chromosome 15 (10/20) (50%). Euchromatin material was found in 13 cases by various banding and FISH techniques, while in six of 20 sSMCs there was no evidence of euchromatin material. Parental karyotypes could be evaluated in 15 cases and familial inheritance was found in only three of them (20%). We conclude that the proposed strategy for the identification and characterization of sSMCs is accurate and represents a good alternative to novel FISH techniques for modestly equipped cytogenetic laboratories.

Molecular cytogenetic characterization of two small chromosome 8 derived supernumerary mosaic markers

Two small supernumerary mosaic marker chromosomes (SMC) were identified by conventional cytogenetics, one prenatally, the other postnatally. Fluorescence in situ hybridization (FISH) techniques, including 24-color FISH, were applied to identify both SMCs and better characterize their constitution. Patient 1: a 29 year-old man, whose wife had a spontaneous abortion, was found to have a small ring of the pericentromeric region of chromosome 8 (47,XY,+r(8)(p11q11)/46,XY). Patient 2: a 37 year-old woman had amniocentesis. The fetus was found to have a SMC; its presence was confirmed postnatally. Several FISH techniques (24-color, whole chromosome paints, centromeres, telomeres, band 8p22) led to the identification of a small analphoid marker. The marker was an inversion-duplication for part of the short arm of chromosome 8 (47,XY,+inv dup (8)(p23pter)/46,XY). The 24-color FISH allowed us to conclude that both markers originated exclusively from chromosome 8. However, the structure and content of the markers were elucidated using other molecular cytogenetic techniques, showing their complementarity.

Prenatal diagnosis of partial tetrasomy 14: a case study

Prenatal specimens were received from a fetus with abnormalities noted on ultrasound. A supernumerary marker chromosome (SMC) was detected: 47,XY,+mar. Fluorescence in situ hybridisation (FISH) further classified this to be partial tetrasomy for chromosome 14. We compare this finding with other cases of SMC (14) and further classify phenotype with karyotype.

Prenatal identification of de novo marker chromosomes using micro-FISH approach

Chromosome microdissection combined with polymerase chain reaction (PCR) and reverse chromosome painting ('micro-FISH') is a powerful technique for the unequivocal identification of complex or subtle chromosomal aberrations. We have applied this technique to the prenatal diagnosis of three fetuses with de novo marker chromosomes. One small supernumerary satellited marker chromosome was shown to have originated from the fusion of the centromeric heterochromatin of one or both of chromosomes 14 and 22. The second marker was identified as i(9)(p10) while the third marker chromosome was shown to have been derived from the 1p13.1-1q21.3 region. At birth, the clinical outcome correlated well with that expected from the prenatal cytogenetic findings. Our study highlights the importance of the application of 'micro-FISH' to prenatal diagnosis.

A molecular and FISH approach to determining karyotype and phenotype correlations in six patients with supernumerary marker(22) chromosomes

In a cytogenetic, molecular, and clinical study of patients with autosomal supernumerary marker chromosomes (SMC), 6 out of 72 (8.3%) were shown by fluorescence in situ hybridisation (FISH) to be derived from chromosome 22. PCR microsatellite analysis and FISH using primers and cosmids from proximal 22q showed 3 of the 6 to contain euchromatin. The first, a de novo nonmosaic bisatellited, dicentric SMC, was acsertained in a patient with cat eye syndrome and Duane anomaly. Microsatellite analysis showed the SMC was maternal in origin with euchromatin extending to D22S427, i.e., proximal to the DiGeorge syndrome critical region (DGSCR). The second, a nonmosaic bisatellited, dicentric marker, was found in a child with severe hypotonia and developmental delay and had been inherited from the patient's phenotypically normal father. FISH showed the SMC to contain euchromatin extending into the DGSCR. The third, a de novo SMC, was ascertained antenatally and was shown to contain 22q euchromatin extending distal to the DGSCR. The 19-week terminated fetus was phenotypically normal at autopsy. Two of the three SMC(22)s not containing detectable proximal 22q euchromatin were ascertained coincidentally in phenotypically normal individuals, whereas the third, the only mosaic with a minority euploid cell line, was found in a patient with mild developmental delay. These results suggest that SMC(22)s devoid of proximal 22q euchromatin are not associated with adverse phenotypic effects whereas SMC(22)s containing euchromatin may be found in individuals with phenotypes ranging from cat eye syndrome to normal.

Molecular cytogenetic study of supernumerary marker chromosomes in an unselected group of children

We report on an unselected group of 24 children with small supernumerary marker chromosomes, found in a large sample of 34,910 consecutive newborns karyotyped at birth. Sixteen of these were available for reexamination. With the use of in situ hybridization with alpha-satellite centromere probes and satellite III, ribosomal and beta-satellite DNA probes, we have characterized these markers. In 14 of the 16 cases we have been able to determine the chromosomal origin of the marker. Twelve of the markers are derived from the acrocentric chromosomes. Of these 12 markers, 4 are derived from chromosome 14, 4 from chromosome 22, 3 from chromosome 15 and one is from either chromosome 13 or 21. Ten of these markers were initially ascertained with the satellite III DNA probe, taking advantage of the fact that satellite III DNA is found in the centromeric region of the following chromosomes: 1, 5, 9, 13, 14, 15, 16, 20, 21, 22, and Y. Two markers were derived from chromosomes 4 and 8. The origin of the last 2 markers could not be determined with the techniques employed. Only one of these children is psychometrically retarded and has a peculiar appearance. Unfortunately we were not able to determine the origin of the marker in her case. All other children developed normally.

Involvement of chromosome 22 in ependymomas

We have karyotyped a total of twelve ependymomas using GTG-banding including seven for which preliminary results have already been published. One case showing hyperdiploid main line with two marker chromosomes was further analyzed by nonisotopic chromosome in situ suppression hybridization. It was shown that the marker chromosomes consisted of 1q, 14q and 1q, and 22q. The possible role of chromosome 22 in ependymomas and the usefulness of fluorescence in situ hybridization for cytogenetic analysis in tumor investigation are discussed.

Characterization of marker chromosomes by microdissection and fluorescence in situ hybridization

We characterized by microdissection and fluorescence in situ hybridization (FISH) two marker chromosomes: (1) a de novo, acrocentric marker chromosome detected in 88 per cent of the amniotic fluid cells of one of two physically and developmentally normal twins; and (2) a metacentric marker chromosome present in a phenotypically normal female. Analysis of FISH probes developed from the marker chromosomes indicated that the marker chromosomes in cases 1 and 2 were del(14)(q11) and a derivative chromosome from a Robertsonian translocation, respectively. Microdissection in combination with FISH may prove to be a valuable technique in determining the chromosomal origin of de novo marker chromosomes and unbalanced structural rearrangements detected during prenatal diagnosis.

Application of fluorescent in situ hybridization for 'de novo' anomalies in prenatal diagnosis

Fluorescent in situ Hybridization (FISH) was carried out for three cases of abnormal karyotypes in prenatal studies. Two concerned de novo structural anomalies and the third a marker chromosome. The origin of the extra material could be defined in all three cases, which gives a better insight into the relationship between genotype and phenotype and makes more adequate genetic counselling possible.

Molecular cytogenetic characterization of marker chromosomes found at prenatal diagnosis

The nature and origin of two de novo small marker chromosomes found at prenatal diagnosis were determined by fluorescence in situ hybridization using chromosome centromere-specific probes and chromosome-specific plasmid libraries. One marker was found in a mosaic state and was shown to be an i(18p). The second marker was characterized as an inv dup(22). We conclude that molecular cytogenetic analysis contributes to the identification of marker chromosomes and therefore facilitates genetic counselling and decision-making for the parents.