Chromosomes in the Cornelia de Lange syndrome

Summary This paper summarizes previous chromosomal studies in patients with the Cornelia de Lange syndrome showing abnormal karyotypes. We report on 45 cases of the Cornelia de Lange syndrome clinically examined by one of us (B. B.) and chromosomally studied using several different methods. Two abnormal karyotypes were found: a girl with a 45,X karyotype and a boy with a (13q14q) translocation which was also found in his phenotypically normal mother and maternal grandmother. Because of recent reports of the duplication 3q syndrome and Comelia de Lange-like phenotypes, prometaphase chromosomes were studied in 31 patients. All karyotypes were normal. As there was an excess of boys among the younger patients, special examination for the fragile site on X(q28) was carried out. This abnormality was not found. Even though no patients with the dup(3q) syndrome were found among the Cornelia de Lange patients, chromosome studies are recommended especially in connection with genetic counselling. A recurrence rate of 2–5% must still be considered for the Cornelia de Lange syndrome.     

Multiple de novo mutations in the MECP2 gene

Rett syndrome is an X-linked dominant disorder that usually arises following a single de novo mutation in the MECP2 gene. Point mutation testing and gene dosage analysis of a cohort of British Rett syndrome patients in our laboratory revealed four females who each had two different de novo causative mutations, presumed to be in cis because the patients showed no deviation from the classical Rett syndrome phenotype. Two of these cases had a point mutation and a small intraexonic deletion, a third had a whole exon deletion and a separate small intraexonic deletion, and a fourth case had a small intraexonic deletion and a large duplication. These findings highlight the necessity to perform both point mutation analysis and exon dosage analysis in such cases, particularly because of the possibility of undetected parental mosaicism and the implications for prenatal diagnosis in future pregnancies. These cases also suggest that the MECP2 gene may be particularly prone to multiple mutation events.     

X0 Karyotype in a phenotypic male

Summary A 24-year-old male with ambiguous genitalia was found to have a predominantly 45,X chromosomal constitution. The clinical and cytological findings in this patient are presented in the report. The possible mode of origin of this aberrant phenotype due to chromosome mosaicism of 45,X/46,XY type during early embryogenesis and subsequent elimination of 46,XY cell line is discussed.     

Macrocephaly-cutis marmorata telangiectatica congenita: report of a patient with a translocation

Cutis marmorata telangiectatica congenita (CMTC) is a rare cutaneous disorder. More than one half of the patients with CMTC have additional extra-cutaneous associated congenital anomalies. A subset of patients with CMTC have macrocephaly, the M-CMTC syndrome. This is a report on a patient with the M-CMTC syndrome and a de novo translocation t(2;17)(p11;p13). The etiology and pathology of the M-CMTC syndrome is unknown. Suggestions for the cause for M-CMTC include the occurrence of a new dominant mutation in a single gene, deletion of multiple contiguous genes at a level beyond the resolution of conventional karyotyping and chromosomal mosaicism. This patient did not have chromosomal mosaicism, however he had a translocation. It can be postulated that in the present patient the translocation breakpoints disrupted one or more genes entailing skin lesions but also other features: mental retardation, macrocephaly and facial dysmorphia.     

Chromosome banding study of the Cornelia de Lange syndrome

Summary Chromosome studies were performed on 13 patients with the Cornelia de Lange syndrome. With the technique of chromosome banding analysis, no chromosomal abnormalities were found.     

A de novo t (X;8)(p11.2;q24.3) demonstrating Cornelia de Lange syndrome phenotype

Cornelia de Lange syndrome is a rare syndrome of hitherto unknown etiology. We present a 9-months old female patient with de novo t (X;8) (p11.2;q24.3) and Cornelia de Lange Syndrome phenotype. De novo t (X;8)(p11.2;q24.3) was not reported so far in Cornelia de Lange syndrome.     

Localized chromosomal mosaicism as a cause of dysmorphic development

Regional chromosomal mosaicism has been found in tissue from the clitoral mass of an infant presenting with ambiguous genitalia. Chromosome analysis of skin from the clitoral mass was interpreted as 46,XX/52,XX, +2, +7, +8, +12, +13, +20, whereas study of ovarian tissue and peripheral lymphocytes found each to have normal 46,XX karyotypes with no indication of mosaicism. We believe that somatic cell mutation led to a hyperdiploid clonal cell line resulting in maldevelopment of this patient's external genitalia. This observation, which to our knowledge has not been previously reported, indicates that localized chromosomal abnormalities in some cases may be etiologic of isolated congenital malformations.     

Cytogenetic instability of dental pulp stem cell lines

Human adult stem cells (hASCs) offer a potentially renewable source of cell types that are easily isolated and rapidly expanded for use in regenerative medicine and cell therapies without the complicating ethical problems that are associated with embryonic stem cells. However, the eventual therapeutic use of hASCs requires that these cells and their derivatives maintain their genomic stability. There is currently a lack of systematic studies that are aimed at characterising aberrant chromosomal changes in cultured ASCs over time. However, the presence of mosaicism and accumulation of karyotypic abnormalities within cultured cell subpopulations have been reported. To investigate cytogenetic integrity of cultured human dental stem cell (hDSC) lines, we analysed four expanded hDSC cultures using classical G banding and fluorescent in situ hybridisation (FISH) with X chromosome specific probe. Our preliminary results revealed that about 70% of the cells exhibited karyotypic abnormalities including polyploidy, aneuploidy and ring chromosomes. The heterogeneous spectrum of abnormalities indicates a high frequency of chromosomal mutations that continuously arise upon extended culture. These findings emphasise the need for the careful analysis of the cytogenetic stability of cultured hDSCs before they can be used in clinical therapies.     

Partial trisomy 3q in a child with sacrococcygeal teratoma and Cornelia de Lange syndrome phenotype

Partial duplication of 3q is a rare chromosomal disorder that leads to multiple congenital abnormalities such as growth retardation, microcephaly and characteristic facial features. Although the phenotype of the patient has similarities with Cornelia de Lange Syndrome they are etiologically different. We report here a 9 months old baby boy with partial duplication of 3q and features similar with Cornelia De Lange syndrome. Conventional cytogenetic analysis revealed a derivative chromosome 21. In order to determine the origin of this chromosome region we used subtelomeric FISH technique. Based on the results of all these cytogenetic studies and the physical examinations, the diagnosis is partial 3q duplication.     

Somatic mosaicism in cases with small supernumerary marker chromosomes

Somatic mosaicism is something that is observed in everyday lives of cytogeneticists. Chromosome instability is one of the leading causes of large-scale genome variation analyzable since the correct human chromosome number was established in 1956. Somatic mosaicism is also a well-known fact to be present in cases with small supernumerary marker chromosomes (sSMC), i.e. karyotypes of 47,+mar/46. In this study, the data available in the literature were collected concerning the frequency mosaicism in different subgroups of patients with sSMC. Of 3124 cases with sSMC 1626 (52%) present with somatic mosaicism. Some groups like patients with Emanuel-, cat-eye- or i(18p)- syndrome only tend rarely to develop mosaicism, while in Pallister-Killian syndrome every patient is mosaic. In general, acrocentric and non-acrocentric derived sSMCs are differently susceptible to mosaicism; non-acrocentric derived ones are hereby the less stable ones. Even though, in the overwhelming majority of the cases, somatic mosaicism does not have any detectable clinical effects, there are rare cases with altered clinical outcomes due to mosaicism. This is extremely important for prenatal genetic counseling. Overall, as mosaicism is something to be considered in at least every second sSMC case, array-CGH studies cannot be offered as a screening test to reliably detect this kind of chromosomal aberration, as low level mosaic cases and cryptic mosaics are missed by that.     

Mechanisms leading to uniparental disomy and their clinical consequences

Uniparental disomy (UPD) refers to the situation in which both copies of a chromosome pair have originated from one parent. In humans, it can result in clinical conditions by producing either homozygosity for recessive mutations or aberrant patterns of imprinting. Furthermore, UPD is frequently found in conjunction with mosaicism for a chromosomally abnormal cell line, which can also contribute to phenotypic abnormalities. Investigations into the mechanisms by which UPD may arise have helped to expand our general awareness of the impact of chromosomal abnormalities and chromosomal mosaicism in normal human development. Specifically, it appears that errors in the transmission of a chromosome from parent to gamete and during early somatic cell divisions are remarkably common but that embryo and cell selection during early embryogenesis help to ensure the presence of a numerically balanced chromosome complement in the developing fetus. UPD is also likely to occur within a portion of cells in all individuals simply as a consequence of somatic recombination occurring during mitotic cell divisions. This can be an important step in cancer development as well as a contributing factor to other late onset diseases. This review summarizes mechanisms by which UPD may arise and their associated clinical consequences.     

Mosaicism in 45,X Turner syndrome: does survival in early pregnancy depend on the presence of two sex chromosomes?

Summary Cytogenetic and molecular genetic findings in 91 patients with Turner syndrome are reported. In 87 patients, chromosome studies were carried out both in lymphocyte and fibroblast cultures. Mosaicism was demonstrated in 58 of these patients (66.7%), whereas only 18 (20.7%) were apparent non-mosaic 45,X, and 11 patients (12.6%) showed non-mosaic structural aberrations of the X chromosome. Among the mosaic cases 16 (18.4% of all patients) displayed a second cell line containing small marker chromosomes. The association of Y-specific chromosomal material with the presence of marker chromosomes was demonstrated in 6 out of 7 mixoploid fibroblast cell lines by polymerase chain reaction amplification and by Southern-blot analysis. The observation of ring formation and morphological variability in vivo and in vitro, and the continous reduction in the percentage of cells containing marker chromosomes in longterm cultivation experiments indicated an increased instability of marker chromosomes. The findings suggest that in vivo selection of structurally altered sex chromosomes exists. Thus, the observation of apparent non-mosaic 45,X chromosomal complements in liveborn individuals with Turner syndrome does not contradict the hypothesis that some degree of mosaicism is necessary for survival in early pregnancy.     

Evidence for high frequency of chromosomal mosaicism in spontaneous abortions revealed by interphase FISH analysis.

Numerical chromosomal imbalances are a common feature of spontaneous abortions. However, the incidence of mosaic forms of chromosomal abnormalities has not been evaluated. We have applied interphase multicolor fluorescence in situ hybridization using original DNA probes for chromosomes 1, 9, 13, 14, 15, 16, 18, 21, 22, X, and Y to study chromosomal abnormalities in 148 specimens of spontaneous abortions. We have detected chromosomal abnormalities in 89/148 (60.1%) of specimens. Among them, aneuploidy was detected in 74 samples (83.1%). In the remaining samples, polyploidy was detected. The mosaic forms of chromosome abnormality, including autosomal and sex chromosomal aneuploidies and polyploidy (31 and 12 cases, respectively), were observed in 43/89 (48.3%) of specimens. The most frequent mosaic form of aneuploidy was related to chromosome X (19 cases). The frequency of mosaic forms of chromosomal abnormalities in samples with male chromosomal complement was 50% (16/32 chromosomally abnormal), and in samples with female chromosomal complement, it was 47.4% (27/57 chromosomally abnormal). The present study demonstrates that the postzygotic or mitotic errors leading to chromosomal mosaicism in spontaneous abortions are more frequent than previously suspected. Chromosomal mosaicism may contribute significantly to both pregnancy complications and spontaneous fetal loss.     

A possible clinical implication of homozygous inversions of 9qh regions with Cornelia de Lange syndrome (CLS)

Several investigators have attempted to correlate chromosomal abnormalities with Cornelia de Lange Syndrome (CLS), but none of them have been conclusive. The homozygous inversion of 9qh found in the present case has not been found previously. It remains to be clarified whether the presence of this finding in CLS was simply a coincidence or whether homozygosity for such inversions may result in CLS.     

De Lange Syndrome: Report of 20 Cases

Typus Degenerativus Amstelodamensis or Amsterdam dwarfism, a syndrome of unknown etiology characterized by mental retardation, a distinctive face, characteristic hands and feet, defective growth and other minor malformations, was first described by Cornelia de Lange in 1933. Approximately 69 cases, including nine autopsies, have been reported in the literature. In this paper we present a further 20, with illustrations of the syndrome from infancy to puberty (including de Lange''s original three cases). The historical, physical, laboratory and radiographic findings of de Lange''s three patients and our 20 are tabulated. Autopsy findings in one of our patients are reported and the literature is briefly reviewed.Although some observers have recently reported chromosome abnormalities in de Lange''s syndrome, we feel that the diagnosis is made from the history and physical examination and that there are no definitive laboratory aids which can confirm the diagnosis. Chromosome studies in all 20 of our patients were normal and the genetic implications are discussed.     

A Euploid Line of Human Embryonic Stem Cells Derived from a 43,XX,dup(9q),+12,-14,-15,-18,-21 Embryo

Aneuploid embryos diagnosed by FISH-based preimplantation genetic screening (PGS) have been shown to yield euploid lines of human embryonic stem cells (hESCs) with a relatively high frequency. Given that the diagnostic procedure is usually based on the analysis of 1–2 blastomeres of 5 to 10-cell cleavage-stage embryos, mosaicism has been a likely explanation for the phenomena. However, FISH-based PGS can have a significant rate of misdiagnosis, and therefore some of those lines may have been derived from euploid embryos misdiagnosed as aneuploid. More recently, coupling of trophectoderm (TE) biopsy at the blastocyst stage and array-CGH lead to a more informative form of PGS. Here we describe the establishment of a new line of hESCs from an embryo with a 43,XX,dup(9q),+12,-14,-15,-18,-21 chromosomal content based on array-CGH of TE biopsy. We show that, despite the complex chromosomal abnormality, the corresponding hESC line BR-6 is euploid (46,XX). Single nucleotide polymorphism analysis showed that the embryo´s missing chromosomes were not duplicated in BR-6, suggesting the existence of extensive mosaicism in the TE lineage.     

Maternal de novo triple mosaicism for two single <Emphasis Type="Italic">OCRL</Emphasis> nucleotide substitutions (c.1736A>T,c.1736A>G) in a Lowe syndrome family

Since the identification of the Lowe’s oculocerebrorenal syndrome gene, more than 100 distinct OCRL mutations have been observed. Germline mosaicism has rarely been detected in Lowe families; however, the presence of mosaic mutations, in particular triple mosaicism, may often remain undiagnosed. In the course of OCRL analysis in a Polish family, the index case showed a hemizygous nucleotide transition (c.1736A>G, p.His507Arg). Gene analysis in the patient’s mother not only provided evidence that she is a carrier of the mutant allele transmitted to her son but also showed an additional c.1736A>T (p.His507Leu) transversion affecting the same base position. DNA from a mouthwash sample from the mother showed a similar fluorescence intensity pattern at the affected nucleotide. These data, together with the findings that maternal grandparents solely showed wildtype sequence, implied a de novo mosaicism in the mother. Triple X syndrome was ruled out by karyotype analysis and a partial or complete gene duplication could be excluded. Allele-specific amplification confirmed the results of three alleles being present in the mother. The amount of wildtype allele detected in qPCR implied the presence of cells solely harboring c.1736A and single-cell PCR experiments confirmed the presence of non-mutant cells in the mother’s blood. These data suggest that the mutations observed are the result of two de novo events in early embryogenesis of the mother. To the best of our knowledge, this is the first observation of triple mosaicism at a single nucleotide.     

Familial ring (20) chromosomal mosaicism

Summary Ring (20) chromosomal mosaicism defined by two cell lines (one normal and the other with the ring) has been demonstrated in lymphocyte and fibroblast cultures from three members of a family through two generations. Two carriers of the ring chromosome were affected and showed the typical signs of r(20) syndrome including mental retardation, microcephaly, behavioral disorders, and epilepsy. The epilepsy is characterized by complex partial seizures sometimes evolving secondarily into generalized tonic-clonic seizures and is poorly controlled by or resistant to medical treatment. The mother of the two patients, also a carrier of ring (20) chromosomal mosaicism, was clinically and phenotypically normal and did not exhibit any signs of epilepsy. Lymphocyte and fibroblast cultures from the most severely affected sib, the proband, contained the highest percentage of cells with ring (20) chromosome and revealed the greatest instability of the ring. Though it is assumed that the ring (20) chromosome arose from terminal breakage and reunion in both arms, no loss of genetic material could be documented cytogenetically. Yet the question arises of how ring chromosomal mosaicism can be passed on. One explanation might be that a chromosome 20 predisposed to terminal lesions or breaks is transmitted from the mother to her offspring. Inherited instability of this type might lead to de novo formation of the ring.     

Clinical outcome and follow-up of the first reported case of Russell-Silver syndrome with the unique combination of maternal uniparental heterodisomy 7 and mosaic trisomy 7

BACKGROUND: Russell-Silver syndrome (RSS) has been associated with maternal uniparental disomy (UPD) for chromosome 7 although the etiology of the syndrome is still unknown. Cases of RSS associated with maternal UPD7 have involved isodisomies, heterodisomies, and mixed isodisomy with heterodisomy simultaneously. This publication is a follow-up report of the postnatal clinical outcome of the first prenatally suspected case of combined mosaic trisomy 7 with maternal uniparental disomy of chromosome 7 (UPD7). CASE: The diagnosis of RSS in the proband was suspected prenatally because trisomy 7 mosaicism (47,XX,+7[13]/46,XX[19]) and maternal uniparental heterodisomy 7 were both found in amniotic fluid cells. Cord blood karyotype analysis showed only disomic cells (46,XX[50]), whereas postpartum chorionic villus analysis was completely trisomic for chromosome 7 (47,XX,+7[19]). Postnatally, the diagnosis of RSS was confirmed by physical findings, her trisomy 7 mosaicism was confirmed by cytogenetic analysis of her skin biopsy (47,XX,+7[9]/46,XX[20]) and her UPD7 was confirmed on both peripheral blood and skin biopsy using microsatellite markers. During infancy, the proband experienced growth deficiency, persistent hypoglycemia, and psychomotor developmental delay. CONCLUSIONS: Trisomic rescue as a life-saving mechanism, with subsequent chromosomal mosaicism in combination with UPD may occur more frequently in RSS than has been reported. Systematic testing of cases suspected prenatally or postnatally would be informative regarding the individual contribution of each factor. Imprinting, loss of heterozygosity for recessive genes, and mosaicism may explain the short stature, asymmetry, and the variable expression of the phenotype. The contribution of these mechanisms to the syndrome should be evaluated in these cases.     

Tetrasomy 9p mosaicism associated with a normal phenotype in two cases

Tetrasomy 9p is a rare chromosomal syndrome and about 30% of known cases exhibit mosaicism. Approximately 50 of the reported cases with tetrasomy 9p mosaicism show a characteristic facial appearance, growth failure, and developmental delay. However, 3 patients with mosaicism for isochromosome 9p and a normal phenotype have also been reported. We report 2 additional cases of clinically normal young females with tetrasomy 9p mosaicism, one of whom also exhibited X chromosome aneuploidy mosaicism leading to an overall of 6 different cell lines. STR analysis performed on this complex mosaic case indicated that the extra isochromosome was of maternal origin while the X chromosome aneuploidy was of paternal origin, indicating a postzygotic event.