Subtelomeric familial translocation t(2;7)(q37;q35) leading to partial trisomy 7q35-->qter: molecular cytogenetic analysis and clinical phenotype in two generations.

Few patients with trisomy of the most distal region of chromosome 7q have been described. We report on a familial translocation t(2;7)(q37;q35) leading to trisomy 7q35-->7qter in a child and her paternal uncle and a minimal deletion of distal 2q as demonstrated by FISH with probes located in the chromosome 2q subtelomeric region. The clinical phenotype included macrocephaly and low-set ears, also found in other reported patients trisomic for the distal part of chromosome 7q. Phenotypic findings probably useful for the clinical diagnosis include normal size at birth, large head with frontal bossing, low-set ears of normal shape, small nose and low nasal bridge, feeding difficulties in infancy, and severe neurodevelopmental delay.

Application of fluorescence in situ hybridization to the identification of different marker chromosomes.

Chromosome studies performed on lymphocyte culture of a baby with specific dysmorphism and congenital anomalies suggestive of trisomy 21 revealed a mosaicism: 46,XY,rea(21q21q) [25]/47,XY,rea(21q21q),+mar1[25]. The karyotype of the mother is normal, but the father's karyotype presents an supernumerary chromosome greater and different from the marker of his son: 47,XY,+mar2 (100%). The identification of the two marker chromosomes by standard cytogenetic techniques followed by molecular techniques is essential for the identification of the origin of these two chromosomes. The unusual presence of two different markers one in the father and one in the son, as well as the clinical features of the child, are presented. The possible role of the paternal marker, in the de novo chromosomal rearrangement in his child will be discussed.

Fluorescent in-situ hybridization on human embryos showing cleavage arrest after freezing and thawing.

Our current freezing-thawing policy is to transfer only embryos that cleave further in the 24 h following thawing. The purpose of our study was to investigate the incidence of numerical abnormalities for chromosomes X, Y and 1 in blastomeres of human preimplantation embryos that survived cryopreservation but did not cleave further after thawing. A total of 63 embryos surviving a freezing-thawing cycle but not cleaving further within 24 h after thawing were screened. Of the 63 screened embryos that showed cleavage arrest 24 h after thawing, 56 embryos (88.9%) remained arrested 48 h after thawing and slightly more than half of these (29/56; 51.8%) showed further deterioration in morphological quality. Seven embryos (11.1%) showed signs of further cleavage; five embryos showed additional cleavage of one blastomere and two developed a blastocoelic cavity. Fluorescent in-situ hybridization (FISH) with three specific probes for simultaneous detection of chromosomes X, Y and 1 was performed and was successful in 60 out of 63 embryos. Of these successfully labelled embryos, 26 (43.3%) were in the diploid range: 12 (20%) were uniformly diploid for the chromosomes X, Y and 1; three embryos showed aneuploidy in all their blastomeres (two were XXY-karyotype and one was monosomy 1) and in 11 embryos nondisjunction was detected. Thirteen embryos were categorized as being either haploid, triploid, tetraploid or hexaploid. Nine embryos were classified as mosaic and 12 as being highly abnormal or chaotic. These preliminary results suggest that a large proportion of embryos that do not cleave further after freezing and thawing carry chromosomal aberrations. This finding supports our policy of not transferring cryopreserved embryos which do not cleave further 24 h following thawing.

Triple colour fluorescent in-situ hybridization for chromosomes X,Y and 1 on spare human embryos.

The potential for implantation of human embryos obtained by in-vitro fertilization is presumably determined to a large extent by their chromosomal constitution but cytogenetic analysis of preimplantation embryos has been hampered by a number of practical and technical problems. With the advent of fluorescent in-situ hybridization (FISH) a practical method for numerical chromosomal analysis has become available. A limited amount of data has been obtained with FISH on human embryos using probes binding to chromosomes X, Y, 16, 18 and 13/21 combined or for chromosomes X and Y or 1 and 17. It was our purpose to extend these data by the combined analysis of chromosomes X, Y and 1 in spare human embryos. A short fluorescent in-situ hybridization procedure involving the simultaneous use of three deoxyribonucleic acid probes detected with red, green, and a mixture of red and green was used to determine chromosomal abnormalities in 116 spare embryos with a poor morphological score and/or displaying one or more multinucleated blastomeres. The majority of the embryos was obtained by intracytoplasmic sperm injection. Less than half of the embryos (n = 54) were diploid and only 39 of them were uniformly XY11 or XX11; two embryos showed a non-disjunction and 13 embryos were aneuploid. Of the remainder, 22 were mosaic, nine were either haploid, triploid or tetraploid and 12 embryos were classified as chaotic. The latter pattern was particularly frequent in multinucleated blastomeres. Our data are comparable with those obtained with FISH using other chromosomal probes and confirm that the majority of preimplantation embryos carry a numerical chromosomal defect. Aneuploidy for chromosome 1 does not appear to be more common in preimplantation embryos than is reported for other chromosomes. Although the high incidence of chromosomal anomalies is presumably biased by the fact that only embryos with a poor morphological score were analysed, it nevertheless indicates that natural selection is the foremost reason for the low implantation rates of human preimplantation embryos in in-vitro fertilization (IVF) programmes.

Mosaic tetrasomy 15q25-->qter in a newborn infant with multiple anomalies.

We describe a premature boy with metopic craniosynostosis, facial anomalies, atrial-septal defect, hydronephrosis and flexion contractures of lower limbs, and mosaic tetrasomy 15q25-->qter. The extra chromosome material was present in the form of an acentric marker. A number of clinical manifestations observed in this child were also found in 3 previously reported patients who were trisomic for the same part of chromosome 15 and in 2 patients who were tetrasomic for a larger segment of 15q.

Proximal deletion of chromosome 21 confirmed by in situ hybridization and molecular studies.

Foetal blood sampling was performed at 35 weeks of gestation due to abnormal foetal ultrasound findings. There was apparent monosomy 21 (45,XX,-21) in all mitoses analyzed. The infant died at 37 weeks during delivery. Examination disclosed facial anomalies, clubfeet, hypoplasia of the left urogenital tract, agenesis of corpus callosum, ventricular dilatation, and heterotopias. Reevaluation of the karyotype showed an unbalanced translocation t(1;21) (q44;q22.11) which resulted from a maternal balanced translocation. These findings were confirmed by fluorescence in situ hybridization and molecular studies with chromosome 21 specific markers. The latter showed a proximal deletion of the maternally derived chromosome 21 including all loci from centromere down to the D21S210 locus. This case illustrates the need for complementary cytogenetic and molecular investigations in cases of apparent monosomy 21.

Tubal hydatidiform mole.

We report a tubal hydatidiform mole, most likely resulting from dispermic fertilization. Early hatching of the embryo, because of a defective zona pellucida, may have favored tubal implantation.

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.

Detection of subtle reciprocal translocations by fluorescence in situ hybridization.

Three different subtle reciprocal translocations were detected on long, well-banded chromosomes. The same translocations were examined using fluorescence in situ hybridization (FISH) with chromosome-specific libraries and unique DNA sequences. Our findings show that FISH allows rapid and unequivocal detection and characterization of this type of chromosome rearrangement. This approach is especially useful for prenatal diagnosis when one of the parents is a balanced carrier of such small fragment translocations.

Familial Turner syndrome.

A 28-year-old Turner female with secondary amenorrhea is described, who showed 45,X/46,X,del(Xp) mosaicism in her blood lymphocytes and a 46,X,del(Xp) karyotype only in her ovaries. 45,X/46,XX mosaicism was found in the patient's mother, who presented short stature, mild Turner dysmorphism and had a normal reproductive life-span. Phenotypic implications of the cytogenetic findings in the patients are discussed, and literature data on fertility in Turner syndrome are briefly reviewed.

Interstitial deletion and ring chromosome derived from 19q. Proximal 19q trisomy phenotype.

A small supernumerary ring chromosome has been found in a boy with overweight, dysmorphic facies and mental retardation. His mother had an interstitial deletion of the long arm of chromosome 19 and the same ring chromosome. By means of fluorescence in situ hybridization the ring chromosome was shown to be derived from the deleted chromosome, after the occurrence of two breaks: one in the centromere region, the other in the q-arm of chromosome 19.

Pallister-Killian syndrome: characterization of the isochromosome 12p by fluorescent in situ hybridization.

The isochromosome 12p (i(12p)) in fibroblasts of 3 patients with Pallister-Killian syndrome and one decreased prematurely born neonate, was characterized by fluorescent in situ hybridization (FISH) using chromosome 12-specific DNA probes. FISH is a useful technique for rapid and reliable detection and characterization of the i(12p) chromosome in Pallister-Killian patients. Detection was possible also in interphase cells. In addition, the in vitro selection against i(12p) cells at different passages in fibroblast cultures of two patients was monitored.

Chromosome analysis in human oocytes unfertilized in vitro: a mathematical model for the estimation of the first meiotic non-disjunction frequency.

The results of cytogenetic analysis of unfertilized human oocytes in an in-vitro fertilization programme are to a large extent influenced by the methodology used. Exact conclusions cannot be drawn due to technical and interpretational errors. A mathematical model was constructed, therefore, to estimate the weight of these errors and to calculate the exact frequency of first meiotic non-disjunction in IVF oocytes. Of 246 prepared oocytes only 105 could be karyotyped exactly. Using the classical method of calculation, an aneuploidy frequency of 39% was obtained. By applying the maximum likelihood method a correlation between the frequency of first meiotic non-disjunction and the interpretational error level was found. Loss of chromosomes by anaphase lagging seemed to be undetectable, but the probability of chromosome loss due to fixation and unhomogeneous spreading was found to be 20%. Accepting an error level of 10-20%, the true non-disjunction frequency expected should range between 20 and 40%. This model yields a standard curve which can offer a basis for comparison of results obtained in different studies.

Familial meningioma. Case report with cytogenetic study.

A family is presented of which two members were shown to have an intracranial meningioma. We performed a chromosome study in the affected living individual and several other relatives, with special attention for chromosome 22 anomalies. In neither of them a chromosomal abnormality could be detected. However, in view of the recent cytogenetic findings reported in meningioma, it is suggested that karyotyping should be performed in every family with two or more members affected by meningioma.

The significance of pericentric inversions of chromosome 2.

Thirteen new cases of a pericentric inversion 2 collected from different laboratories are reported. In addition 41 cases of a pericentric inversion 2 were reviewed from the literature. The pooled data were analysed using Weinberg's proband method to evaluate the risk of a carrier for either children with congenital anomalies or reproductive wastage. In the "corrected" sample of 166 lifeborn offspring of carriers of a pericentric inversion 2 there were five who showed phenotypic anomalies and two died a few hours after delivery. The reported anomalies are heterogeneous and probably reflect the basic risk of any couple for abnormal lifeborn offspring. There has been no observation of a lifeborn who inherited an unbalanced recombination of a parental pericentric inversion 2. A carrier of a pericentric inversion 2 obviously has an increased risk for reproductive wastage. This is indicated by (1) an increase of the rate of spontaneous abortions and (2) an increase of the rate of index patients ascertained because of previous miscarriages. The risk of a carrier of a pericentric inversion 2 for a spontaneous abortion or a stillbirth may be about twice the basic risk of the general population.