Diploid/tetraploid/t(1;6) mosaicism in a 17-year-old female with hypomelanosis of Ito, multiple congenital anomalies, and body asymmetry.

Many types of chromosome mosaicism have been identified in cases of hypomelanosis of Ito, often in association with chromosome instability; however, there have been very few cases with diploid-tetraploid mosaicism described in the literature. We present a patient with a tetraploid mosaicism: a 17-year-old girl who has hypomelanosis of Ito in association with diploid/tetraploid/t(1;6) mosaicism. She had multiple congenital anomalies of omphalocele, exstrophy of bladder, duodenal web, and imperforate anus. These features have not been described previously in diploid-tetraploid mosaicism.

Prenatal diagnosis of holoprosencephaly (HPE) in a fetus with a recombinant (18)dup(18q)inv(18)(p11.31q11.2)mat.

Alobar holoprosencephaly (HPE) was identified by ultrasonography at 18 weeks' gestation in a fetus of a 29-year-old G2P0A1 woman. HPE has been described in association with various chromosomal anomalies. Amniocentesis was performed and a rearrangement of chromosome 18 resembling an isochromosome for the long arm of chromosome 18 was found. Subsequently, the mother was found to have a pericentric inversion of chromosome 18 with breakpoints at p11.31 and q11.2. The karyotype of the fetus was re-interpreted as 46,XX, rec(18)dup(18q)inv(18)(p11.31q11.2)mat. This is the first case of a parental inversion leading to a deficiency of 18p11.31 to 18pter associated with HPE.

Holoprosencephaly, sacral anomalies, and situs ambiguus in an infant with partial monosomy 7q/trisomy 2p and SHH and HLXB9 haploinsufficiency..

We report an infant with holoprosencephaly (HPE), sacral anomalies, and situs ambiguus with a 46,XY,der(7)t(2;7)(p23.2;q36.1) karyotype as a result of an adjacent-1 segregation of a t(2;7)pat. The chromosomal abnormality was diagnosed prenatally after sonographic detection of HPE in the fetus. The baby was born at 37 weeks gestation, and died in the newborn period; he had dysmorphic features consistent with HPE sequence. Postmortem internal evaluation showed semilobar HPE, abdominal situs ambiguus, multiple segments of bowel atresia, dilatation of the ureters, and bony sacral anomalies. Molecular analysis confirmed hemizygosity for the SHH and HLXB9 genes, which are likely to be responsible for the HPE and sacral phenotypes, respectively. Immunohistochemical studies showed intact dopaminergic pathways in the mesencephalon, suggesting that midbrain dopamine neuron induction appears to require only one functioning SHH allele.

Cytogenetic aspects of the Canadian early and mid-trimester amniotic fluid trial (CEMAT).

Cytogenetic results from a large multicentre randomized controlled study of 2108 amniotic fluids obtained at 11+0-12+6 weeks (EA) and 1999 fluids at 15+0-16+6 weeks (MA) were compared. There was no statistically significant difference in the rate of chromosome abnormalities (EA =1.9 per cent; MA=1.7 per cent) or level III mosaicism (EA=0.2 per cent; MA= 0.2 per cent) between the groups. Level I and Level II mosaicism occurred more frequently in MA. Maternal cell contamination was not significantly different between the groups, but maternal cells only were analysed from one bloody EA fluid. The number of repeat amniocenteses because of cytogenetic problems was 2.2 per cent in the EA group compared with only 0.3 per cent in the MA group. On average, culture of EA fluids required one day more than MA fluids. Although both culture success (97.7 per cent) and accuracy (99.8 per cent) were high for patients randomized to the EA group, routine amniocentesis prior to 13 weeks' gestation is not recommended for clinical reasons including an increased risk of fetal loss and talipes equinovarus.

De novo deletion 12q: report of a patient with 12q24.31q24.33 deletion.

We report on a patient with de novo interstitial deletion of the long arm of chromosome 12: 46,XY,del(12)(q24.31q24.33). To our knowledge this is the first patient with this chromosomal abnormality reported. He was born with minor anomalies, ambiguous genitalia, tracheomalacia, and he was developmentally delayed at age 9 months. The phenotype associated with this deletion may be characteristic. However, because of the absence of reported cases of other patients with loss of this chromosomal region, we cannot delineate the specific phenotype further. Ambiguous genitalia or hypogonadism has been reported in other patients with chromosomal rearrangements involving 12q24.

Development and characterization of immortalized fibroblastoid cell lines from an FA(C) mouse model.

Fanconi anemia (FA) is an autosomal recessive disorder, characterised by multiple congenital malformations, bone marrow failure and a predisposition to developing malignancies, especially leukemia. FA cells show increased levels of spontaneous chromosomal aberrations and a hypersensitivity to DNA cross-linking agents such as mitomycin C (MMC) and diepoxybutane (DEB). There are at least eight complementation groups involved in FA, and the genes for two of these groups, FA(A) and FA(C), have been isolated and cloned. Mouse models for FA(C) have been developed by replacing exon 8 or exon 9 of Fac with the neo gene. Mice homozygous for Fac mutations show reduced fertility and hypersensitivity to induction of chromosomal aberrations by MMC and DEB. To facilitate the study of cellular defects in vitro, transformed mouse fibroblast cell lines were established. Cell-killing experiments and cytogenetic analyses were performed on these cells following treatment with MMC and DEB. Fac-/- showed significant hypersensitivity to MMC and DEB as compared with Fac+/+ and +/- for both cellular phenotypes. This is consistent with results obtained from similar studies on human fibroblasts and lymphoblastoid cell lines. Therefore, these isogenic transformed mouse fibroblasts provide as in vitro model for further investigation of the hypersensitivity of Fanconi anemia cells to DNA cross-linking agents.

Multiple congenital anomalies in a fetus with 45,X/46,X,r(X)(p11.22q12) mosaicism.

Ring X chromosomes that do not undergo inactivation may cause malformations and mental retardation. We report on a fetus with anencephaly, total dorsal rachischisis, and diaphragmatic hernia that was found to have a mosaic 45,X/46,X,r(X)(p11.22q12) karyotype. Fluorescent in situ hybridization (FISH) confirmed that the ring chromosome was X-derived. This report expands the phenotypic spectrum of mosaic monosomy X and small ring X chromosomes.

Risk of congenital anomalies in children of parents occupationally exposed to low level ionising radiation.

OBJECTIVES: To evaluate the risk of having a child with a congenital anomaly in relation to occupational exposure to low level ionising radiation in the pre-conception period. METHODS: A case-control study based on the Canadian congenital anomalies registry used record linkage techniques to identify congenital anomalies among male and female workers in Canada's largest electric company. Cases were defined as parents of a child with a congenital anomaly born between April 1979 and December 1986 who had a congenital anomaly diagnosed within the first year of life. Controls were an individually matched sample of parents of a liveborn child without an anomaly. Risk of congenital anomaly was assessed in relation to parental exposure to ionising radiation acquired through work within a nuclear generating station of an electric power company. Exposure was assessed according to employment, whether or not the worker was monitored for radiation exposure, and quantitative estimates of radiation dose. RESULTS: Employment within the electric power industry was not associated with an increased risk of congenital anomalies in the offspring of mothers or fathers. Risk estimates for workers monitored (those who are likely to be exposed to ionising radiation) were 1.75 (95% confidence interval (95% CI) 0.86 to 3.55) for mothers and 0.84 (95% CI 0.68 to 1.05) for fathers. Exposure for fathers before conception, defined cumulatively and for six months before conception, was not associated with increased risk of anomalies in their offspring. There were no significant increases in risk found between type of anomaly and any measure of exposure, although the statistical power in these groups was limited. The study had insufficient numbers to evaluate the effects of ionising radiation in mothers as only three mothers had recorded doses > 0 mSv. CONCLUSIONS: Overall, workers in a nuclear power industry, and specifically those exposed before conception to low levels of ionising radiation, do not appear to be at an increased risk of having a liveborn child with a congenital anomaly.

Roberts syndrome fibroblasts showing cisplatin hypersensitivity have normal host cell reactivation of cisplatin-treated adenovirus and normal capacity of cisplatin-treated cells for adenovirus DNA synthesis.

Roberts syndrome (RS) is a rare, recessively inherited disorder characterized by growth retardation, limb reductions and craniofacial deformities. Cells from a subset of afflicted individuals, termed RS+, display unusual separation or puffing of the heterochromatic regions of their chromosomes and are hypersensitive to several DNA-damaging agents including mitomycin C (MMC) and cisplatin, both of which can induce interstrand crosslinks in DNA. For this reason, we have investigated the ability of RS+ fibroblasts to repair cisplatin-induced DNA lesions using adenoviris as a probe. Host cell reactivation of cisplatin-treated adenovirus (Ad) was significantly reduced in nucleotide excision repair (NER)-deficient xeroderma pigmentosum (XP) cells but was normal in the two RS+ fibroblast strains and the Fanconi's anemia (FA)fibroblast strain tested. The capacity of cisplatin-treated cells for Ad DNA synthesis was reduced in XP and FA cells compared to normal human cells, but was not reduced in RS+ cells. These results indicate that the hypersensitivity of RS+ cells to cisplatin is not due to a deficiency in NER nor due to a deficiency in the pathway which leads to cisplatin hypersensitivity in FA cells. It is possible that the abnormal heterochromatin organisation of RS+ cells selectively renders the heterochromatic regions of the genome more susceptible to mutagen damage and/or less available for repair.

Inactivation of Fac in mice produces inducible chromosomal instability and reduced fertility reminiscent of Fanconi anaemia.

Fanconi anaemia (FA) is an autosomal recessive disease characterized by bone marrow failure, variable congenital malformations and predisposition to malignancies. Cells derived from FA patients show elevated levels of chromosomal breakage and an increased sensitivity to bifunctional alkylating agents such as mitomycin C (MMC) and diepoxybutane (DEB). Five complementation groups have been identified by somatic cell methods, and we have cloned the gene defective in group C (FAC)(7). To understand the in vivo role of this gene, we have disrupted murine Fac and generated mice homozygous for the targeted allele. The -/- mice did not exhibit developmental abnormalities nor haematologic defects up to 9 months of age. However, their spleen cells had dramatically increased numbers of chromosomal aberrations in response to MMC and DEB. Homozygous male and female mice also had compromised gametogenesis, leading to markedly impaired fertility, a characteristic of FA patients. Thus, inactivation of Fac replicates some of the features of the human disease.

Maternal uniparental isodisomy of human chromosome 14 associated with a paternal t(13q14q) and precocious puberty.

Cytogenetic and molecular investigation of a boy with precocious puberty and motor developmental delay revealed a 45,XY,t(14q14q) or i(14q) karyotype with no paternal chromosome 14 contribution. VNTR analysis of loci on four other chromosomes excluded non-paternity with greater than 99% confidence. Results of VNTR and CA repeat analyses of ten loci along the entire length of chromosome 14 were consistent with homozygosity at all loci, suggesting that the chromosomal rearrangement was a maternal isochromosome for 14q. As the proband's father had a balanced Robertsonian translocation, t(13q14q), we suggest that the origin of the maternal uniparental disomy (UPD) was fertilization by a nullisomy 14 sperm with formation of the isochromosome in the early embryo. Also, the proband has several clinical features in common with six previously reported liveborn cases of maternal UPD 14: hypotonia and motor developmental delay, mild dysmorphic facial features, low birth weight and growth abnormalities, and, more specifically, precocious puberty among the four cases old enough to assess. The emergence of a syndrome associated with maternal UPD 14 suggests the possibility of genomic imprinting of regions of chromosome 14, especially a gene involved in the onset of puberty.

Correction of the spontaneous and DEB-induced chromosomal aberrations in Fanconi anemia cells of the FA(C) complementation group by the FACC gene.

Fanconi anemia (FA) cells are hypersensitive to the cytotoxic and clastogenic effects of DNA cross-linking agents. Four complementation groups have been identified to date. The gene (FACC) that corrects the hypersensitivity of one of them, FA(C), has been cloned. In the present study, both the increased spontaneous and diepoxybutane (DEB)-induced chromosomal instability in FA(C) lymphoblastoid cells were corrected by transfection of FACC.

Heterogeneity in Roberts syndrome.

Roberts syndrome (RS) is a rare, autosomal recessive condition characterized primarily by growth retardation, developmental delay, and limb anomalies. Some RS patients (RS+), but not others (RS-), have an abnormality of their constitutive heterochromatin (the "RS effect"). RS+ patients also show a cellular hypersensitivity to DNA damaging agents such as mitomycin C (MMC). Lymphoblastoid cell lines from 2 unrelated RS+ patients were fused and hybrid cells examined for correction of the RS effect and MMC hypersensitivity. Neither cellular defect was corrected in the 2 hybrid cell lines examined, suggesting that these 2 patients represent a single complementation group. Fusions were also performed between one RS+ cell line and 2 different RS- cell lines. In both fusions, the hybrids demonstrated correction of both the heterochromatin abnormality and MMC hypersensitivity. These observations suggest that RS+ and RS- patients belong to different complementation groups and do not arise from the same single gene mutation.

A study of sister chromatid exchange and somatic cell mutation in hospital workers exposed to ethylene oxide.

To investigate the risks of exposure to ethylene oxide (EO) at current permissible levels and at past higher levels, an inception cohort of sterilizer operators and supervisors from the Central Processing Department (CPD), respiratory therapists, and engineers exposed to EO were identified at the McMaster University Medical Centre. A comparison group from Nutrition Services (NUTR) were matched with the CPD workers on the basis of sex, age, and smoking habit. The present report is based on genetic test results for the 94 CPD and matched NUTR workers only. Statistical analysis based on the mean SCE frequency in the top 5, top 10, and all cells (50 cells scored per individual) and high frequency cells (HFC) based on the 95th percentile for nonsmoking control subjects showed a direct association with current smoking but not with EO exposure. Similarly, statistical analysis of the somatic cell mutation (SCMT) variant frequencies did not demonstrate an association with EO exposure, nor with smoking. Regression analysis indicated that sex was the only other covariate that significantly affected SCE. Age was weakly associated with SCMT. A statistically significant interaction between occupational exposure and smoking habits was observed only for the mean SCE frequency of the top 5 and top 10 cells when the 11 current CPD/NUTR pairs were not included. Thus, this interaction should be interpreted with caution.

Case-control study of congenital anomalies in children of cancer patients.

OBJECTIVES: To determine whether the offspring of cancer survivors are at an increased risk of congenital anomalies and whether cancer therapy before conception is associated with such an increase. DESIGN: Case-control study using computerised record linkage. SETTING: Ontario, Canada. SUBJECTS: Parents of children born during April 1979 to December 1986 who had a congenital anomaly diagnosed within the first year of life (45,200 mothers and 41,158 fathers) and a matched sample of parents whose children did not have a congenital anomaly (45,200 mothers and 41,158 fathers). MAIN OUTCOME MEASURES: Cancer diagnosed in either parent before conception and radiotherapy to the pelvis or abdomen or chemotherapy with an alkylating agent. RESULTS: Among the mothers, 54 cases and 52 controls were identified as having had cancer diagnosed in Ontario (relative risk = 1.04, 95% confidence interval 0.7 to 1.5) and among the fathers, 61 cases and 65 controls were identified (0.9, 0.7 to 1.4). No significant associations were found between congenital anomalies in the offspring and any type of cancer treatment in either the mothers or the fathers. CONCLUSIONS: The risk of congenital anomalies among liveborn offspring whose parents have had cancer or been treated for cancer is not higher than that in the general population.

Somatic cell hybridization of Roberts syndrome and normal lymphoblasts resulting in correction of both the cytogenetic and mutagen hypersensitivity cellular phenotypes.

Roberts syndrome (RS) is a rare recessive condition of limb deformities, growth retardation, and developmental delay. Cultured cells from approximately half of RS patients exhibit a "puffing" of the constitutive heterochromatin and a hypersensitivity to mitomycin C (MMC). Patients exhibiting these cellular phenomena are designated RS+. Somatic cell hybridization with normal cells has been shown to correct the heterochromatin abnormality in RS+ cells. To determine if the MMC hypersensitivity could also be corrected by hybridization to normal cells, we fused two different RS+ lymphoblastoid cell lines (LCLs) to a ouabain-resistant, HAT-sensitive, normal LCL. Cytogenetic analyses of hybrid cell lines (HCLs) revealed complete correction of the heterochromatin abnormality. MMC cell killing assays revealed correction of the mutagen hypersensitivity as well. Five of the six HCLs tested exhibited D10 values (the dose at which 10% of the cells survive) that were not significantly lower than that of the normal parent but that were 6- to 18-fold greater than those of the RS+ parents. Correction of both of these cellular phenotypes in RS+ cells by fusion with normal cells supports the hypothesis that both of these phenomena are caused by a common defect in the Roberts syndrome gene (RBS).

Hypersensitivity to mitomycin C cell-killing in Roberts syndrome fibroblasts with, but not without, the heterochromatin abnormality.

Roberts syndrome (RS) is a rare genetic disorder, characterized clinically by severe pre- and post-natal growth retardation and symmetric limb reduction deformities. Some patients with RS have a distinctive abnormality of the constitutive heterochromatin (the RS effect) which has been described as a premature separation of the paracentromeric and nucleolar organizing regions of the chromosomes and the distal portion of the long arm of the Y chromosome (German, 1979). These patients [denoted RS(+)] are clinically indistinguishable from the RS(-) patients who lack the cytogenetic marker for Roberts syndrome. Recently, a mutant in Drosophila has been described which has both heterochromatin undercondensation and hypersensitivity to mutagen treatment (Gatti et al., 1983). The authors suggested that the uncondensed heterochromatin may be more accessible to damage by mutagens. Thus, the present study was an investigation of the mutagen sensitivity in Roberts syndrome, to determine whether there is a similar relationship between abnormal heterochromatin structure and mutagen sensitivity. Plating efficiency experiments were performed with RS(+) fibroblasts, RS(-) fibroblasts, RS heterozygous fibroblasts and a large assortment of appropriate control cells. The RS fibroblasts with the heterochromatin abnormality were consistently more sensitive (based on D10 values) to mitomycin C treatment than were any of the other cell strains tested, including RS(-) cells. These results support the hypothesis that mitomycin C sensitivity and abnormal heterochromatin structure in Roberts syndrome are related.