SC phocomelia syndrome, premature centromere separation, and congenital cranial nerve paralysis in two sisters, one with malignant melanoma

Prenatal and Postnatal Diagnosis and Genetic Background of Corpus Callosum Malformations and Neonatal Follow-Up

INTRODUCTION

The corpus callosum is one of the five main cerebral commissures. It is key to combining sensory and motor functions. Its structure can be pathological (dysgenesis) or completely absent (agenesis). The corpus callosum dys- or agenesis is a rare disease (1:4000 live births), but it can have serious mental effects.

METHODS

In our study, we processed the data of 64 pregnant women. They attended a prenatal diagnostic center and genetic counseling from 2005 to 2019 at the Department of Obstetrics and Gynecology at Semmelweis University.

RESULTS

The pregnancies had the following outcomes: 52 ended in delivery, 1 in spontaneous abortion, and 11 in termination of pregnancy (TOP) cases (n = 64). The average time of detection with imaging tests was 25.24 gestational weeks. In 16 cases, prenatal magnetic resonance imaging (MRI) was performed. If the abnormality was detected before the 20th week, a genetic test was performed on an amniotic fluid sample obtained from a genetic amniocentesis. Karyotyping and cytogenetic tests were performed in 15 of the investigated cases. Karyotyping gave normal results in three cases (46,XX or XY). In one of these cases, postnatally chromosomal microarray (CMA) was later performed, which confirmed Aicardi syndrome (3q21.3-21.1 microdeletion). In one case, postnatally, the test found Wiedemann-Rautenstrauch syndrome. In other cases, it found X ring, Di George syndrome, 46,XY,del(13q)(q13q22) and 46,XX,del(5p)(p13) (Cri-du-chat syndrome). Edwards syndrome was diagnosed in six cases, and Patau syndrome in one case.

CONCLUSIONS

We found that corpus callosum abnormalities are often linked to chromosomal problems. We recommend that a cytogenetic test be performed in all cases to rule out inherited diseases. Also, the long-term outcome does not just depend on the disease's severity and the associated other conditions, and hence proper follow-up and early development are also key. For this reason, close teamwork between neonatology, developmental neurology, and pediatric surgery is vital.

Reduced sister chromatid cohesion acts as a tumor penetrance modifier

Sister chromatid cohesion (SCC) is an important process in chromosome segregation. ESCO2 is essential for establishment of SCC and is often deleted/altered in human cancers. We demonstrate that esco2 haploinsufficiency results in reduced SCC and accelerates the timing of tumor onset in both zebrafish and mouse p53 heterozygous null models, but not in p53 homozygous mutant or wild-type animals. These data indicate that esco2 haploinsufficiency accelerates tumor onset in a loss of heterozygosity (LOH) sensitive background. Analysis of The Cancer Genome Atlas (TCGA) confirmed ESCO2 deficient tumors have elevated number of LOH events throughout the genome. Further, we demonstrated heterozygous loss of sgo1, important in maintaining SCC, also results in reduced SCC and accelerated tumor formation in a p53 heterozygous background. Surprisingly, while we did observe elevated levels of chromosome missegregation and micronuclei formation in esco2 heterozygous mutant animals, this chromosomal instability did not contribute to the accelerated tumor onset in a p53 heterozygous background. Interestingly, SCC also plays a role in homologous recombination, and we did observe elevated levels of mitotic recombination derived p53 LOH in tumors from esco2 haploinsufficient animals; as well as elevated levels of mitotic recombination throughout the genome of human ESCO2 deficient tumors. Together these data suggest that reduced SCC contributes to accelerated tumor penetrance through elevated mitotic recombination.

Tumorigenesis often involves the inactivation of tumor suppressor genes. This often encompasses an inactivation mutation in one allele and loss of the other wild-type allele, referred to as loss of heterozygosity (LOH). The rate at which the cells lose the wild-type allele can influence the timing of tumor onset, and therefore an indicator of a patient’s risk of cancer. Factors that influence this process could be used as a predictive indicator of cancer risk, however these factors are still unclear. We demonstrate that partial impairment of sister chromatid cohesion (SCC), a fundamental component of the chromosome segregation in mitosis and homologous recombination repair, enhanced tumorigenesis. Our data suggest this is through elevated levels of mitotic recombination derived p53 LOH. This study emphasizes the importance of understanding how impaired SCC, mitotic recombination rates, and LOH rates influence cancer risk.

Melanoma and intellectual disability: do prognostic factors at diagnosis differ from general population?

BACKGROUND

Few melanoma cases are reported in individuals with intellectual disability (ID), and prognostic factors at diagnosis are unknown in this population. This work was designed to investigate whether prognostic factors at diagnostic are different in patients with ID compared with a general population.

METHODS

Melanoma cases retrieved from Hérault's Tumour Registry (HTR) from 1995 to 2015 were cross-referenced against a list of adult patients with ID, living in Hérault. Major prognostic factors were compared with those in non-ID melanoma patients included in HTR and in patients followed by Montpellier University Hospital and included in the Réseau pour la Recherche et l'Investigation Clinique sur le Mélanome (RIC-Mel) database.

RESULTS

Ten melanoma cases in individuals with ID were identified and compared with 3804 non-ID melanoma cases in HTR and 1024 non-ID melanoma cases included in RIC-Mel. Mean Breslow thickness at diagnosis was 4.6 mm in melanoma cases among those with ID versus 1.89 mm in HTR (P = 0.109) and 2.36 mm in RIC-Mel (P = 0.156). Stage at diagnosis was superior to stage IIB in 42.9% of ID cases versus 11.4% of non-ID cases in HTR (P < 0.05) and 8.5% in RIC-Mel (P < 0.05).

CONCLUSIONS

Melanomas in patients with ID had less favourable prognostic factors at diagnosis, including higher Breslow thickness and more advanced stage, than melanomas in non-ID patients. These adverse prognostic factors indicate a later diagnosis in this population, leading to a poorer prognosis. This work underlines the need to improve melanoma screening among individuals with ID.

Report of the Phenotype of a Patient with Roberts Syndrome and a Rare ESCO2 Variant

Roberts syndrome is a rare autosomal recessive genetic disease. In this report, we report a Brazilian patient with a rare ESCO2 variant. The patient manifested a broad range of clinical findings including the significant, bilateral shortening of the extremities. He deteriorated and passed away at 20 days of age. High-resolution GTG-banded karyotype showed lack of centromeric constriction in some chromosomes, premature centromere separation in others, and repulsion of the heterochromatin regions. Molecular analysis of the ESCO2 gene revealed a deletion of 4 bp involving exon 4 in homozygosity (NM_00107420.2:c.875_878delACAG), which causes loss of ESCO2 function. We describe the clinical presentation caused by a rare ESCO2 variant.

Long-term survival after corrective surgeries in two patients with severe deformities due to Roberts syndrome: A Case report and review of the literature

Roberts syndrome (RBS; OMIM 268300) is a rare autosomal recessive disease characterized by retardation before and after birth, cranial and maxillofacial deformities, limb anomalies and intellectual disability. Mutations in the establishment of cohesion 1 homologue 2 (ESCO2) gene on chromosome 8p21.1 have been found to be causative for RBS. We describe two patients with RBS with physical deformities and ll. One is an 8-year-old Yemeni male, and the other is his 13-year-old sister. These patients were diagnosed with RBS and underwent surgeries during their first to third years of life. Here, we present the cases for the two patients, focusing specifically on their surgical management and outcomes. Additionally, by reviewing the literature on RBS, we also summarize the proper surgical interventions for this rare disease. This paper describes the long-term follow-up of two patients with severe deformities who benefitted from corrective surgeries. The findings of this study indicate that patients who survive infancy and reach adulthood, even patients who present with severe disease symptoms, can benefit from corrective surgeries and lead better lives.

Expanding the mutation and clinical spectrum of Roberts syndrome

Roberts syndrome and SC phocomelia syndrome are rare autosomal recessive genetic disorders representing the extremes of the spectrum of severity of the same condition, caused by mutations in ESCO2 gene. We report three new patients with Roberts syndrome from three unrelated consanguineous Egyptian families. All patients presented with growth retardation, mesomelic shortening of the limbs more in the upper than in the lower limbs and microcephaly. Patients were subjected to clinical, cytogenetic and radiologic examinations. Cytogenetic analysis showed the characteristic premature separation of centromeres and puffing of heterochromatic regions. Further, sequencing of the ESCO2 gene identified a novel mutation c.244_245dupCT (p.T83Pfs*20) in one family besides two previously reported mutations c.760_761insA (p.T254Nfs*27) and c.764_765delTT (p.F255Cfs*25). All mutations were in homozygous state, in exon 3. The severity of the mesomelic shortening of the limbs and craniofacial anomalies showed variability among patients. Interestingly, patient 1 had abnormal skin hypopigmentation. Serial fetal ultrasound examinations and measurements of long bones diagnosed two affected fetuses in two of the studied families. A literature review and case comparison was performed. In conclusion, we report a novel ESCO2 mutation and expand the clinical spectrum of Roberts syndrome.

Genome stability: What we have learned from cohesinopathies

Cohesin is a multiprotein complex involved in many DNA-related processes such as proper chromosome segregation, replication, transcription, and repair. Mutations in cohesin gene pathways are responsible for human diseases, collectively referred to as cohesinopathies. In addition, both cohesin gene expression dysregulation and mutations have been identified in cancer. Cohesinopathy cells are characterized by genome instability (GIN) visualized by a constellation of markers such as chromosome aneuploidies, chromosome aberrations, precocious sister chromatid separation, premature centromere separation, micronuclei formation, and sensitivity to genotoxic drugs. The emerging picture suggests that GIN observed in cohesinopathies may result from the synergistic effects of the multiple cohesin dysfunctions. © 2016 Wiley Periodicals, Inc.

Can corruption of chromosome cohesion create a conduit to cancer?

Cohesin is a conserved multisubunit protein complex with diverse cellular roles, making key contributions to the coordination of chromosome segregation, the DNA damage response and chromatin regulation by epigenetic mechanisms. Much has been learned in recent years about the roles of cohesin in a physiological context, whereas its potential and emerging role in tumour initiation and/or progression has received relatively little attention. In this Opinion article we examine how cohesin deregulation could contribute to cancer development on the basis of its physiological roles.

The expanding universe of cohesin functions: a new genome stability caretaker involved in human disease and cancer

Cohesin is responsible for sister chromatid cohesion, ensuring the correct chromosome segregation. Beyond this role, cohesin and regulatory cohesin genes seem to play a role in preserving genome stability and gene transcription regulation. DNA damage is thought to be a major culprit for many human diseases, including cancer. Our present knowledge of the molecular basis underlying genome instability is extremely limited. Mutations in cohesin genes cause human diseases such as Cornelia de Lange syndrome and Roberts syndrome/SC phocomelia, and all the cell lines derived from affected patients show genome instability. Cohesin mutations have also been identified in colorectal cancer. Here, we will discuss the human disorders caused by alterations of cohesin function, with emphasis on the emerging role of cohesin as a genome stability caretaker.

Detection of premature segregation of centromeres in persons exposed to ionizing radiation

We have analyzed the frequency of premature centromeric division (PCD) in medical personnel professionally exposed to low doses of radiation. They had chromosome aberrations (CAs) involving dicentric chromosomes, ring chromosomes, acentric fragments, chromosome breaks, and chromatid breaks. The study included 30 exposed subjects and 23 controls who were each analyzed by a conventional cytogenetics procedure and subsequently by fluorescent in situ hybridization (FISH). The latter was applied particularly in order to verify PCD in a specific chromosome (chromosome 18) in both metaphases and interphase nuclei. The results revealed a significant difference (p < 0.001) in frequencies between the two groups (exposed and controls) for all the observed variables (CAs), metaphases with PCD (MPCD), total number of chromosomes with PCD (TPCD), number of PCD metaphases in acrocentric chromosomes (MAPCD), and the total number of acrocentric chromosomes with PCD (TAPCD). The doses of ionizing radiation absorbed by the subjects' bodies were measured with thermoluminescent dosimeters once a month during the duration of occupational exposure. They were expressed in mSv, as mean annual effective doses for the period of exposure. The Spearman rank test showed a high positive correlation between total life effective dose and frequency of CAs and PCD. Based on the results obtained in this study, we suggest that PCD, as a phenomenon manifesting chromosomal instability (CIN), should be considered as a suitable cytogenetic biomarker for individuals occupationally exposed to ionizing radiation.

Roberts-SC syndrome, a rare syndrome and cleft palate repair

Roberts SC syndrome is a rare syndrome with only 17 previously recognized patients reported in medical literature. The syndrome is characterized by multiple malformations, particularly, symmetrical limb reduction, craniofacial anomalies such as bilateral cleft lip and palate, micrognathia, and severe growth and mental retardation. Our patient, a young child of five years having Roberts-SC, was successfully operated for cleft palate under general anesthesia. The main features of the syndrome and the technical problems of anesthesia and surgery are discussed in this report.

The molecular mechanism underlying Roberts syndrome involves loss of ESCO2 acetyltransferase activity

Roberts syndrome/SC phocomelia (RBS) is an autosomal recessive disorder with growth retardation, craniofacial abnormalities and limb reduction. Cellular alterations in RBS include lack of cohesion at the heterochromatic regions around centromeres and the long arm of the Y chromosome, reduced growth capacity, and hypersensitivity to DNA damaging agents. RBS is caused by mutations in ESCO2, which encodes a protein belonging to the highly conserved Eco1/Ctf7 family of acetyltransferases that is involved in regulating sister chromatid cohesion. We identified 10 new mutations expanding the number to 26 known ESCO2 mutations. We observed that these mutations result in complete or partial loss of the acetyltransferase domain except for the only missense mutation that occurs in this domain (c.1615T>G, W539G). To investigate the mechanism underlying RBS, we analyzed ESCO2 mutations for their effect on enzymatic activity and cellular phenotype. We found that ESCO2 W539G results in loss of autoacetyltransferase activity. The cellular phenotype produced by this mutation causes cohesion defects, proliferation capacity reduction and mitomycin C sensitivity equivalent to those produced by frameshift and nonsense mutations associated with decreased levels of mRNA and absence of protein. We found decreased proliferation capacity in RBS cell lines associated with cell death, but not with increased cell cycle duration, which could be a factor in the development of phocomelia and cleft palate in RBS. In summary, we provide the first evidence that loss of acetyltransferase activity contributes to the pathogenesis of RBS, underscoring the essential role of the enzymatic activity of the Eco1p family of proteins.

Defective cohesin is associated with age-dependent misaligned chromosomes in oocytes

Aneuploidy often results from chromosome misalignment at metaphases. Oocytes from senescence-accelerated mice (SAM) exhibit increased chromosome misalignment with age, which originates from nuclear factors. This work sought to further characterize the underlying defects of chromosome misalignments. Using immunofluorescence microscopy with specific antibodies, several specific components associated with spindles or chromosomes, including centrosomes, centromeres and cohesin complex were examined. No obvious differences were found in the distribution of centrosome focus at the spindle pole of oocytes from young and aged SAM, regardless of chromosome alignments, although cytoplasmic centrosome foci were significantly reduced in aged SAM (P < 0.0001). Oocytes from both young and aged SAM exhibited centromere-associated protein-E (CENP-E) at centromeres of all chromosomes, including misaligned chromosomes from aged SAM, demonstrating that CENP-E did not contribute to chromosome misalignments. Notably, both meiotic cohesin proteins located between sister chromatids, REC8 (recombinant 8), STAG3 (stromal antigen 3) and SMC1beta, were remarkably reduced in oocytes from aged SAM. Further, degradation of the cohesin was even more obvious in SAM than in hybrid F1 mice with age, which may explain why SAM are vulnerable to aneuploidy. This natural ageing mouse model shows that defective cohesin coincides with increased incidence of chromosome misalignment and precocious separations of sister chromatids.

Inactivating mutations in ESCO2 cause SC phocomelia and Roberts syndrome: no phenotype-genotype correlation

The rare, autosomal recessive Roberts syndrome (RBS) is characterized by tetraphocomelia, profound growth deficiency of prenatal onset, craniofacial anomalies, microcephaly, and mental deficiency. SC phocomelia (SC) has a milder phenotype, with a lesser degree of limb reduction and with survival to adulthood. Since heterochromatin repulsion (HR) is characteristic for both disorders and is not complemented in somatic-cell hybrids, it has been hypothesized that the disorders are allelic. Recently, mutations in ESCO2 (establishment of cohesion 1 homolog 2) on 8p21.1 have been reported in RBS. To determine whether ESCO2 mutations are also responsible for SC, we studied three families with SC and two families in which variable degrees of limb and craniofacial abnormalities, detected by fetal ultrasound, led to pregnancy terminations. All cases were positive for HR. We identified seven novel mutations in exons 3-8 of ESCO2. In two families, affected individuals were homozygous--for a 5-nucleotide deletion in one family and a splice-site mutation in the other. In three nonconsanguineous families, probands were compound heterozygous for a single-nucleotide insertion or deletion, a nonsense mutation, or a splice-site mutation. Abnormal splice products were characterized at the RNA level. Since only protein-truncating mutations were identified, regardless of clinical severity, we conclude that genotype does not predict phenotype. Having established that RBS and SC are caused by mutations in the same gene, we delineated the clinical phenotype of the tetraphocomelia spectrum that is associated with HR and ESCO2 mutations and differentiated it from other types of phocomelia that are negative for HR.

Rothmund-Thomson syndrome and RECQL4 defect: splitting and lumping

Rothmund-Thomson Syndrome (RTS) is a rare autosomal recessive genodermatosis with a heterogeneous clinical profile. Mutations in RECQL4, encoding a RecQ DNA helicase, are present in a large fraction, but not all clinically diagnosed patients, allowing to classify RTS among the RecQ helicase chromosomal instability defects including Bloom's and Werner's syndromes. Results of RECQL4 test coupled to the variable clinical presentation favored the splitting of RTS clinical phenotype into nosological entities under distinct genetic control. In parallel, lumping of the RECQL4 gene to two other diseases, RAPADILINO and Baller-Gerold has paved the way to unravel through allelic heterogeneity complex genotype-phenotype correlations. Recql4 knockout mice provided crucial insights into the comprehension of the functional role of RECQL4 helicase, which have been corroborated by the initial biochemical characterization of RECQL4 protein and its acting pathway and by studies on RECQL4 homologs in yeast and Xenopus. A role for RECQL4 in initiation of DNA replication and in sister chromatid cohesion has been proposed, which currently fits the pieces of evidence achieved by different approaches. Further work is needed to define the specific and shared functions of RECQL4 in relation to other RecQ helicases and to connect RECQL4 diseases to other genomic instability syndromes with birth defects and cancer predisposition.

Recapitulation of the Roberts syndrome cellular phenotype by inhibition of INCENP, ZWINT-1 and ZW10 genes

Roberts syndrome is an autosomal recessive disorder characterised primarily by symmetric reduction of all limbs and growth retardation. Patients have been reported to have premature separation of heterochromatin regions of many chromosomes and abnormalities in cell cycle. Given the rarity of the syndrome, the linkage analysis approach is not suitable to identify the responsible gene. In this work, a cell line derived from a patient affected by Roberts syndrome was characterized by cell biology and molecular cytogenetics, including comparative genomic hybridization and spectral karyotype. No recurrent chromosomal rearrangements were identified. Thereafter, based on the fact that premature chromatide separation is a reliable marker of the disease, we used antisense oligonucleotide technologies to inhibit six genes involved in various steps of the correct chromosome segregation, such as chromosome cohesion, kinetochore assembling, spindle checkpoint and spindle formation. We found that the inhibition of INCENP, ZWINT-1, ZW10 genes results in the appearance of mitotic cells characterised by centromere separation, chromosome aneuploidy and micronuclei formation. In addition, INCENP, ZWINT-1, ZW10 antisense-treated chromosome morphology was very similar to that of Roberts chromosome when analysed by atomic force microscopy. We concluded that INCENP, ZWINT-1, ZW10 gene inhibition results in cellular phenocopies of Roberts syndrome. Taken together, these findings support a possible role of these genes in the pathogenesis of Roberts syndrome.

Multiple congenital contractures (congenital multiple arthrogryposis)

Arthrogryposis, is the occurrence of joint contractures of variable etiology that start prenatally. Arthrogryposis may result from neurologic deficit, neuromuscular disorders, connective tissue abnormalities, amniotic bands, [figure: see text] or fetal crowding. Arthrogryposis may result from no apparent hereditary causes (neuropathic, for example) or may be the result of hereditary factors (myopathic form, for example). Ultrasound diagnosis depends on observation of scant or absent motion of fetal extremities. Prognosis depends on the specific etiology of the contractures.

Novel assay for Roberts syndrome assigns variable phenotypes to one complementation group

Roberts syndrome (RS) is a rare autosomal recessive disorder characterized by heterogeneous clinical features, the most notable being tetraphocomelia, cleft lip, and cleft palate. Cells derived from most RS patients exhibit abnormal cytogenetic and cellular phenotypes that include the premature separation of para- and pericentromeric heterochromatin visible on C-banded metaphase chromosomes, a phenomenon referred to as heterochromatic splaying. Previously, it was shown that these abnormal phenotypes can be complemented following somatic cell hybridization between RS cells and control cells. In the current study, a permanent cell line was established from a new RS patient with a more severe phenotype than represented by previously established cells in culture. With a newly developed assay designed to facilitate rapid evaluation of in vitro complementation, we assigned this new patient to the same genetic complementation group defined by other, less severely affected patients. The results demonstrate that a single complementation group defines RS patients with heterochromatic splaying regardless of clinical severity.

Cell proliferation rate and nuclear morphometry in Roberts syndrome

Roberts syndrome (RS) is a rare autosomal recessive disorder characterized primarily by symmetric reduction anomalies of all limbs, growth retardation and craniofacial abnormalities. Most RS patients are reported to present a typical abnormality of their constitutive heterochromatin, accompanied by abnormal cytological growth characteristics. We present an extremely severe case of an RS fetus, karyotypically documented, with a clinical presentation including growth deficiency, tetraphocomelia, frontal meningocele, craniofacial abnormalities and penile enlargement with hypospadias. Nuclear morphometrical analysis in tissues of various organs revealed a reduced nuclear size in RS as compared to normal controls, and statistically significant differences in morphometric parameters related to the nuclear shape. Immunohistochemical study of the same organs showed a reduced expression of proliferating cell nuclear antigen in the presented case, thus indicating a decreased cell proliferation rate in RS. Our results reconfirm previously reported findings in cultured fibroblasts of RS cases, thereby reinforcing on a histologic level, the hypothesis that reduced cell proliferation may be involved in the growth retardation and the reduction abnormalities observed in RS.

Prenatal diagnosis of Roberts syndrome: two new cases

We report two fetuses with typical anomalies of Roberts syndrome. Prenatal diagnosis was confirmed by the characteristic disjunction of centromeres in amniocytes. We compare these cases with a child who presented with severe Roberts syndrome. We attempted to evaluate quantitatively the centromeric abnormality and the chromosome separation in the different cultures and with different methods. The variability of the clinical manifestations and cytogenetic investigations of this syndrome are reviewed.

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.

Roberts syndrome: a review of 100 cases and a new rating system for severity

Roberts syndrome (RS) is a rare genetic disorder characterized by pre- and postnatal growth retardation, limb defects, and craniofacial anomalies. Affected persons have varying degrees of malformations involving symmetric reduction in the number of digits, and length or presence of bones in the arms and legs. Craniofacial malformations involve hypertelorism, hypoplastic nasal alae, and a high incidence of cleft lip and palate. Familial and sporadic cases have been reported consistent with an autosomal recessive mode of inheritance. Mitotic cells from many individuals with RS display a characteristic cytogenetic phenomenon consisting of repulsion of heterochromatic regions near centromeres, particularly of chromosomes 1, 9, 16, and splaying of the short arms of the acrocentrics and of the distal Yq. Mitosis in RS cells is abnormal in metaphase duration and anaphase progression. Specifically, anaphase figures show a higher degree of chromosomes that are outlying, lagging, or prematurely advancing toward the poles compared to normal controls. RS cells have abnormal nuclear morphology and also show a higher frequency of micronucleation than normal cells, presumably as a result of the abnormal mitotic events during anaphase. Therefore, RS has been interpreted as a human mitotic mutation syndrome which leads to secondary developmental defects. This report reviews 100 cases of RS, summarizes the phenotypic, genetic, cytogenetic, and cell biology findings in Roberts syndrome, and introduces the RS Rating for quantitating severity.

Studies of mitotic and centromeric abnormalities in Roberts syndrome: implications for a defect in the mitotic mechanism

Roberts syndrome is an inherited human condition that is of particular interest because separation of centromeres and constitutive heterochromatin is observed in metaphase chromosomes. In this study we investigated the frequency of other cytological abnormalities in three Roberts syndrome patients. Our findings when taken with previous cytological reports emphasize that there are other features that are equally characteristic of Roberts syndrome: (1) aneuploidy with random chromosome loss and (2) micronuclei and/or nuclear lobulations of 8%-24% of interphase cells. We observed abnormal chromosome movement involving one or all the chromosomes during anaphase. Evidence is presented suggesting that aneuploidy, micronuclei and abnormal nuclear morphology are a direct result of lagging chromosomes. The cytological features documented for Roberts syndrome indicate that this is a human mitotic mutant.

A sibship with Roberts/SC phocomelia syndrome

We report on a family in which 3 sibs have Roberts/SC phocomelia syndrome. One child has survived to age 9 years. The clinical manifestations and the natural history of this syndrome are reviewed.

The Baller-Gerold syndrome: phenotypic and cytogenetic overlap with Roberts syndrome

A case is reported where the major clinical features of craniostenosis and radial aplasia led to an initial diagnosis of Baller-Gerold syndrome. Mild fibular hypoplasia on skeletal survey led to review of the diagnosis and the similarity of the facial phenotype to that of Roberts syndrome was noted. Chromosome analysis showed the premature centromere separation characteristic of this condition. This case raises the question as to whether the Baller-Gerold syndrome can be considered as a distinct entity. It is suggested that cases diagnosed as having Baller-Gerold syndrome should have cytogenetic analysis and that known Roberts syndrome survivors are reviewed for signs of craniostenosis.

Mitotic disturbance associated with mosaic aneuploidies

The association of various unsystematic aneuploidies with premature centromere division (PCD) was observed in a patient with conspicuous clinical features and combined immunodeficiency. Trisomies and monosomies of almost all autosomes and gonosomal aberrations were found separately or in combination in a majority of the proband's lymphocytes and fibroblasts. The chromosome number varied from 44 to 50. A high proportion of the metaphases showed PCD or had the appearance of C-anaphases. These findings probably represent a new mutant affecting mitosis and causing mosaic aneuploidies.

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.

Prenatal detection of Roberts-SC phocomelia syndrome: report of 2 sibs with characteristic manifestations

We describe 2 sibs with Roberts-SC phocomelia syndrome. Although an ultrasound scan performed at 13 weeks of gestation failed to identify specific abnormalities, repeat scan at 17 weeks detected tetraphocomelia. Ultrasonography can reliably detect Roberts-SC phocomelia prenatally; however, serial scans may be needed. Postmortem examination of the proposita confirmed the sonographic findings and also disclosed dysplastic kidneys and ovarian dysgenesis. The degree of phenotypic variation observed between the sibs supports the hypothesis that Roberts syndrome and SC phocomelia represent a single genetic entity.

A case of interstitial deletion of 10q25.2----q26.1

A de novo interstitial deletion of chromosome 10, del(10)(pter----q25.2::q26.1----qter), was detected in a newborn female with facial anomalies, failure to thrive, and subsequent developmental delay. This case is compared with 10 previous reports of monosomy 10q within the q25----qter region.

Further delineation of the Yunis-Varon syndrome

A boy with intrauterine growth retardation, microcephaly, dysostosis of the skull, hypoplastic facial bones, labiogingival retraction, agenesis of the clavicles, distal aphalangia, and severely hypoplastic thumbs and halluces is described. The features are consistent with the Yunis-Varon syndrome. Review of published reports shows this to be a generalised disorder with variable manifestations in the skeletal, ectodermal, and cardiovascular systems. The consanguinity of the parents of the present case is in agreement with autosomal recessive inheritance.

Incidental detection of premature centromere separation in amniocytes associated with a mild form of Roberts syndrome

Premature centromere separation (PCS) was detected in amniocytes after an amniocentesis was done because of markedly elevated maternal serum alpha-fetoprotein values in a healthy primiparous young woman. PCS has been associated with the Roberts-SC phocomelia syndrome (RS). By 23 weeks' gestation, ultrasonic evaluations did not reveal abnormal fetal development. The pregnancy continued and a male infant was born with mild manifestations of RS. PCS was confirmed in cord blood lymphocytes. This case illustrates that PCS, when detected in amniotic fluid cell cultures, requires a thorough evaluation.

Rhabdomyosarcoma in Roberts syndrome

A 23-month-old child diagnosed as having Roberts syndrome, born to consanguineous parents, developed a sarcoma botryoides. Cytogenetic evaluation of peripheral blood lymphocytes and tumor cells showed premature centromere separation, which is characteristic of Roberts syndrome.

C-anaphases in lymphocyte cultures versus premature centromere division syndromes

Different cases in which chromosomes obtained from short-term lymphocyte cultures appear with separated centromeres are reviewed. These include: (1) C-anaphases in the colchicine-resistance mutation, (2) C-anaphases as a common variant, (3) premature centromere division (PCD) in elderly women, (4) PCD in Alzheimer's disease, (5) early splitting and puffing of centromeres in Roberts' syndrome.