De novo balanced chromosome rearrangements in prenatal diagnosis

OBJECTIVE

We surveyed the datasheets of 29 laboratories concerning prenatal diagnosis of de novo apparently balanced chromosome rearrangements to assess the involvement of specific chromosomes, the breakpoints distribution and the impact on the pregnancy outcome.

METHOD

By means of a questionnaire, data on 269.371 analyses performed from 1983 to 2006 on amniotic fluid, chorionic villus and fetal blood samples were collected.

RESULTS

A total of 246 balanced anomalies were detected at frequencies of 72% for reciprocal translocations, 18% for Robertsonian translocations, 7% for inversions and 3% for complex chromosome rearrangements. The total frequencies of balanced rearrangements were 0.09%, 0.08% and 0.05% on amniotic fluid, chorionic villus and fetal blood samples.

CONCLUSION

A preferential involvement of chromosomes 22, 7, 21, 3, 9 and 11 and a less involvement of chromosomes X, 19, 12, 6 and 1 was observed. A nonrandom distribution of the breakpoints across chromosomes was noticed. Association in the location of recurrent breakpoints and fragile sites was observed for chromosomes 11, 7, 10 and 22, while it was not recorded for chromosome 3. The rate of pregnancy termination was about 20%, with frequencies decreasing from complex chromosomal rearrangements (33%), reciprocal translocations (24%) to inversions (11%) and Robertsonian translocations (3%).

Cytogenetic and molecular evaluation of 241 small supernumerary marker chromosomes: Cooperative study of 19 Italian laboratories

PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Unbalanced segregation of a complex four-break 5q23–31 insertion in the 5p13 band in a malformed child

A rec(5)dup(5)(q23.2q31.3) inherited from a maternal ins(5)(p13.1q23.2q31.3) was detected in a 4-month-old male child who showed hypotonia, microcephaly, cardiac defects, pulmonary hypoplasia and stenosis, bilateral hydronephrosis, hydrocele, testicular hypoplasia and phimosis. Dysmorphisms were also observed. We compare the clinical characteristics of our patient with those of the previously reported dup5q cases in an attempt to define the phenotype-karyotype correlation. The maternal insertion responsible for the duplicated 5q23.2-31.3 region in the child was characterized in detail by FISH analysis, which identified a complex rearrangement involving four breakpoints (bkp's): a 5q segment excised following breakage at 5q23.2 and 5q31.3 became inverted and inserted at 5p13.1, probably coincidentally with an internal breakage at 5q23.3 causing a 180 degrees rotation of the two subsegments. The mother's karyotype was consequently defined as 46,XX, ins(5)(pter --> p13.1 Colon, two colons q23.3 --> q23.2 Colon, two colons q31.3 --> q23.3 Colon, two colons p13.1 --> q23.2 Colon, two colons q31.3 --> qter). There are clusters of Alu sequences in the genomic clones spanning all the four bkp's, suggesting their possible involvement in the rearrangement. No clinical phenotype was associated with this balanced rearrangement in the mother and a number of other carriers in the same family.

Reproductive follow-up of carriers of familial reciprocal balanced translocations involving chromosome 9 and comparison with predicted outcome

Reproductive follow-up of carriers of familial reciprocal balanced translocations involving chromosome 9 and comparison with predicted outcome: Chromosome 9 is commonly implicated in reciprocal translocations (rcp). Twenty-seven families segregating rcp involving chromosome 9 were selected with the aim of comparing the theoretical risk of Mental Retardation with Congenital Anomalies (MCA/MR) calculated according to Human Cytogenetics Forum with the observed reproductive follow-up. The 27 families include 157 subjects. The reproductive follow-up showed that the majority of mothers underwent full-term pregnancies (88/130), and that there were 37 spontaneous and five voluntary abortions. Eighty-one subjects were karyotyped: 18 had a normal karyotype, 50 carried an rcp, ten had an unbalanced rcp-related karyotype and three an abnormal rcp-unrelated karyotype. Of the 88 live-born individuals, seven had an abnormal rcp-related karyotype with partial chromosome 9 trisomy (four cases) or partial 9p monosomy (three cases), and 48 were rcp carriers, two of whom also presented additional anomalies. The evaluation of reproductive outcomes in the 27 families studied revealed good concordance between the Human Cytogenetics Forum predictions and the observed follow-up in relation to the most probable mode of unbalance at birth, and the higher risk of MCA/MR in rcp carriers with unbalanced live-borns in comparison with those generating healthy progeny

Thyroid hemiagenesis and elevated thyrotropin levels in a child with Williams syndrome

A girl with Williams syndrome (WS) presented with elevated thyrotropin (TSH) levels (7.0 microU/ml), normal free thyroid hormone concentrations, and absent antithyroid autoantibodies. Thyroid ultrasonography and scintigraphy showed hemiagenesis of the left lobe and no evidence of ectopic tissue. TSH response to thyrotropin-releasing hormone (TRH) injection (200 microg/mq, i.v.) was exaggerated and prolonged, suggesting subclinical hypothyroidism. The biological activity of circulating TSH was slightly below the normal range [TSH bioactivity (B) to immunoreactivity (I) ratio (TSH B/I) = 0.4, normal: 0.6-2.2]. These abnormalities are similar to those seen in patients with hypothalamic hypothyroidism. Thyroid function is not a recognized manifestation of WS and is not routinely investigated. However, abnormalities of the hypothalamic-pituitary-thyroid (HPT) axis and thyroid dysgenesis have been found in other WS cases. Genes mapping at 7q11.23, contiguous to the chromosomal region deleted in most WS patients, may be involved in the development of the thyroid gland, contributing to the complex phenotype of WS.

A rare chromosome 5 heterochromatic variant derived from insertion of 9qh satellite 3 sequences

A rare chromosome 5 heterochromatic variant not linked to any clinical sign was identified in a three-generation family. After performing conventional cytogenetics characterization, fluorescence in situ hybridization of D9Z1 indicated that the unusually large qh region of chromosome 5 originated from 9qh, whereas the centromere of the variant chromosome was 5-specific as demonstrated by primed in situ DNA labelling. FISH of probes targeting satellite 3 and beta-satellite sequences of 9qh showed that only satellite 3 sequences were present in the variant 5qh region.

The predictive value of cytogenetic diagnosis after CVS based on 4860 cases with both direct and culture methods

Cytogenetic analysis was performed in 4860 chorionic villus samples by means of both direct preparation and long-term culture. The results of the analysis were compared with a classification including all theoretical types of combinations between the chromosomal constitution of the cytotrophoblast, extraembryonal mesoderm, and fetus, with the aim of evaluating the cytogenetic variability along the trophoblast-embryo axis. Eighteen of 29 possible combinations were found demonstrating a considerable heterogeneity. A mosaic conceptus was found in 1.5 per cent of cases, with generalized mosaicisms and confined mosaicisms in 0.2 and 1.3 per cent, respectively. Cytogenetic variability along the trophoblast-embryo axis was found in 1.42 per cent of cases. Results possibly leading to diagnostic errors (false-positive and false-negative results) were found in only 1.38 per cent. False-positive results of direct preparation were the most commonly observed discrepancy (0.8 per cent), while the incidence of false-positive results of the culture method and of both methods was 0.31 and 0.16 per cent respectively. The incidence of false-negative results was 0.1 per cent, with false-negative results of direct preparation 0.08 per cent and false-negative results of both methods 0.02 per cent. False-negative results of the culture method were not found. Our data confirm the high diagnostic accuracy of chorionic villus sampling and the utility of the combined use of the two methods in minimizing diagnostic errors and in reducing the need for follow-up amniocentesis.

'Late' chorionic villus sampling: cytogenetic aspects

Cytogenetic data about 145 chorionic villus samples obtained between the 13th and 35th week of gestation are reported. 'Late' chorionic villus sampling (CVS) was used to resolve different situations: failed amniotic fluid cell cultures (5 cases); confirmation of an abnormal karyotype, previously diagnosed as mosaic (14 cases); and ultrasound fetal malformation (23 cases). Most of the samples (103 cases) were analysed for the classical indications and in these cases, the principal aim was to obtain a rapid fetal karyotype. Excluding the cases used to check fetal karyotype, a chromosomal aberration was found in 11 out of 131 biopsies. In four cases of the group in which the fetal karyotype was checked (14 cases), the pathology observed at the first diagnosis was confirmed, while in the remaining ten cases the anomaly was not observed.

Technical aspects and diagnostic problems of direct chromosome analysis using chorionic villus sampling in the first trimester

This paper describes 18 months' experience of direct chromosome analysis applied to villi aspirated during the first trimester, using a catheter inserted trans-cervically. A total of 325 biopsy samples were analysed, and there was a diagnostic failure in 6 of these cases (1.8%). An abnormal karyotype was detected in 12 cases (3.8%); three of them were chromosome mosaics not confirmed on amniotic fluid cultures drawn between the 16th and 18th week of gestation. Cytogenetic control was performed on fetal tissues after voluntary abortion. There was a karyotype discrepancy between the placenta and the fetus in two cases out of the 12 mentioned above.

The use of amniotic FSH levels in resolving a discrepancy between fetal chromosomal and phenotypic sex

We report a case in which a discrepancy emerged between the prenatal diagnosis of female chromosomal sex and male sex at ultrasound examination. The FSH dosage performed on an amniotic fluid sample previously stored confirmed the male phenotype of the fetus. The effectiveness of the AF-FSH level dosage in prenatal diagnosis was taken into consideration.

Five cases of prenatally diagnosed sex chromosome mosaicism

Prenatal detection of chromosome mosaicism is a relatively rare phenomenon and always constitutes a diagnostic problem. The difficulties are much more when the mosaics involve the sex chromosomes, because of the large phenotypic variability in individuals with these abnormalities. We studied 5 cases of true mosaics, 4 of these were prenatally detected, while 1 case was revealed only in the fetal lymphocytes after induced abortion. The limits of amniotic fluid culture with regard to the diagnosis of true mosaics and the difficulties arising in genetic counselling are discussed.

SCE analysis in children exposed to lead emission from a smelting plant

The frequency and location of SCE were evaluated in lymphocytes from peripheral blood cultures of 19 children living in a widely contaminated area and showing an increased absorption of lead. In the comparison between the exposed children and a control group living in an uncontaminated area, no significant differences were found in the mean values of SCE frequencies. The distributions of the SCE between chromosomes were proportional to chromosome length in both groups.