New p57KIP2 mutations in Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is characterized by numerous growth abnormalities and an increased risk of childhood tumors. The gene for BWS is localized in the 11p15.5 region, as determined by linkage analysis of autosomal dominant pedigrees. The increased maternal transmission pattern seen in the autosomal dominant-type pedigrees and the findings of paternal uniparental disomy reported for a subgroup of patients indicate that the gene for BWS is imprinted. Previously, we found p57 ^KIP2 , which is a Cdk-kinase inhibitor located at 11p15, is mutated in two BWS patients. Here, we screened for the mutation of the gene in 15 BWS patients. Received: 25 March 1997 / Accepted: 22 May 1997     

Low frequency of p57KIP2 mutation in Beckwith-Wiedemann syndrome.

Beckwith-Wiedemann syndrome (BWS) is an autosomal dominant disorder of increased prenatal growth and predisposition to embryonal cancers such as Wilms tumor. BWS is thought to involve one or more imprinted genes, since some patients show paternal uniparental disomy, and others show balanced germ-line chromosomal rearrangements involving the maternal chromosome. We previously mapped BWS, by genetic linkage analysis, to 11p15.5, which we and others also found to contain several imprinted genes; these include the gene for insulin-like growth factor II (IGF2) and H19, which show abnormal imprint-specific expression and/or methylation in 20% of BWS patients, and p57KIP2, a cyclin-dependent kinase inhibitor, which we found showed biallelic expression in one of nine BWS patients studied. In addition, p57KIP2 was recently reported to show mutations in two of nine BWS patients. We have now analyzed the entire coding sequence and intron-exon boundaries of p57KIP2 in 40 unrelated BWS patients. Of these patients, only two (5%) showed mutations, both involving frameshifts in the second exon. In one case, the mutation was transmitted to the proband's mother, who was also affected, from the maternal grandfather, suggesting that p57KIP2 is not imprinted in at least some affected tissues at a critical stage of development and that haploinsufficiency due to mutation of either parental allele may cause at least some features of BWS. The low frequency of p57KIP2 mutations, as well as our recent discovery of disruption of the K(v)LQT1 gene in patients with chromosomal rearrangements, suggest that BWS can involve disruption of multiple independent 11p15.5 genes.     

Functional analysis of the p57 KIP2 gene mutation in Beckwith-Wiedemann syndrome

p57 ^KIP2 is a potent tight-binding inhibitor of several G₁ cyclin/cyclin-dependent kinase (Cdk) complexes, and is a negative regulator of cell proliferation. The gene encoding p57 ^KIP2 is located at 11p15.5, a region implicated in both sporadic cancers and Beckwith-Wiedemann syndrome (BWS). Previously we demonstrated that p57 ^KIP2 is imprinted and only the maternal allele is expressed in both mice and humans. We also showed mutations found in p57 ^KIP2 in patients with BWS that were transmitted from the patients’ carrier mothers, indicating that the expressed maternal allele was mutant and that the repressed paternal allele was normal. In the study reported here, we performed functional analysis of the two mutated p57 ^KIP2 genes. We showed that the nonsense mutation found in the Cdk inhibitory domain in a BWS patient rendered the protein inactive with consequent complete loss of its role as a cell cycle inhibitor and of its nuclear localization. We also showed that the mutation in the QT domain, although completely retaining its cell cycle regulatory activity, lacked nuclear localization and was thus prevented from performing its role as an active cell cycle inhibitor. Consequently, no active p57 ^KIP2 would have existed, which might have caused the disorders in BWS patients. Received: 7 November 1998 / Accepted: 19 December 1998     

Assessment of p57(KIP2) gene mutation in Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is an overgrowth disorder involving developmental anomalies, tissue and organ hyperplasia and an increased risk of embryonic tumours (most commonly Wilms' tumour). This multigenic disorder is caused by dysregulation of the expression of imprinted genes in the 11p15 chromosomal region. It may involve paternal uniparental disomy (UPD), loss of imprinting of the IGF2 gene, maternal inherited translocations and trisomy with paternal duplication. Recently, a small proportion of BWS patients has been shown to have a mutation in the paternal imprinted p57(KIP2) gene, which encodes a cyclin-dependent kinase inhibitor and negatively regulates cell proliferation. We screened for p57(KIP2) gene mutations in 21 BWS patients with no 11p15 UPD in leucocyte DNA. All patients had a phenotype typical of BWS. We analysed the entire coding sequence of p57(KIP2), including intron-exon boundaries, by direct sequencing of five PCR-amplified fragments. No mutation was found in the p57(KIP2) gene. Our results are consistent with those of previous studies showing that mutation of p57(KIP2) is infrequent in BWS. Thus, other mechanisms of p57(KIP2) silencing (imprinting errors) and/or other 11p15 genes are probably involved in the pathogenesis of BWS.     

NSD1 mutations are the major cause of Sotos syndrome and occur in some cases of Weaver syndrome but are rare in other overgrowth phenotypes

Sotos syndrome is a childhood overgrowth syndrome characterized by a distinctive facial appearance, height and head circumference >97th percentile, advanced bone age, and developmental delay. Weaver syndrome is characterized by the same criteria but has its own distinctive facial gestalt. Recently, a 2.2-Mb chromosome 5q35 microdeletion, encompassing NSD1, was reported as the major cause of Sotos syndrome, with intragenic NSD1 mutations identified in a minority of cases. We evaluated 75 patients with childhood overgrowth, for intragenic mutations and large deletions of NSD1. The series was phenotypically scored into four groups, prior to the molecular analyses: the phenotype in group 1 (n=37) was typical of Sotos syndrome; the phenotype in group 2 (n=13) was Sotos-like but with some atypical features; patients in group 3 (n=7) had Weaver syndrome, and patients in group 4 (n=18) had an overgrowth condition that was neither Sotos nor Weaver syndrome. We detected three deletions and 32 mutations (13 frameshift, 8 nonsense, 2 splice-site, and 9 missense) that are likely to impair NSD1 functions. The truncating mutations were spread throughout NSD1, but there was evidence of clustering of missense mutations in highly conserved functional domains between exons 13 and 23. There was a strong correlation between presence of an NSD1 alteration and clinical phenotype, in that 28 of 37 (76%) patients in group 1 had NSD1 mutations or deletions, whereas none of the patients in group 4 had abnormalities of NSD1. Three patients with Weaver syndrome had NSD1 mutations, all between amino acids 2142 and 2184. We conclude that intragenic mutations of NSD1 are the major cause of Sotos syndrome and account for some Weaver syndrome cases but rarely occur in other childhood overgrowth phenotypes.     

Trisomy 11p15 and Beckwith-Wiedemann syndrome. Report of two new cases

An association between trisomy 11p15 and Beckwith-Wiedemann syndrome is described in two brothers. The first presented at birth with gigantism and macroglossia, umbilical hernia and abdominal distention, hypoglycemia and atresia of the pulmonary artery, leading to the diagnosis of Beckwith-Wiedemann syndrome. Facial dysmorphism also included: a hypoplastic midface, hypertelorism, and a short nose with a flattened bridge. The karyotype showed a trisomy 11p15 with a monosomy 18p11, due to a t(11;18)(p154;p111)pat. His brother, born a year later, showed the same signs. The association between trisomy 11p15 and Beckwith-Wiedemann syndrome is in certain cases well established.     

Trisomy 11p15 and Beckwith-Wiedemann syndrome. A report of two cases

Summary Two patients with trisomy 11p15 and features of Beckwith-Wiedemann syndrome are reported. The first is a female infant with gigantism, macroglossia, abdominal hypotonia with umbilical hernia, moderate mental retardation, malformative uropathy, and atrial septal defect. Trisomy 11p15 was due to de novo duplication. The second patient was a stillborn (32–33 weeks pregnancy) with an abnormal tongue, posterior diaphragmatic eventration, inner organ congestion mainly of the adrenals. Trisomy 11p15 was due to a t(4;11)(q33;p14)pat. The association of trisomy 11p15 and Beckwith-Wiedemann syndrome is discussed with regard to cytogenetic data and the gene content of 11p, notably the genes coding for insulin and predisposition to Wilms tumour.     

Imprinting status of 11p15 genes in Beckwith-Wiedemann syndrome patients with CDKN1C mutations.

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder characterized by somatic overgrowth, congenital malformations, and predisposition to childhood tumors. Aberrant expression of multiple imprinted genes, including H19, IGF2, KCNQ1OT1, and CDKN1C, has been observed in BWS patients. It has been estimated that mutations in CDKN1C occur in 12-17% of BWS patients. We have screened 10 autosomal dominant pedigrees and 65 sporadic BWS cases by PCR/heteroduplex analysis and DNA sequencing and have identified four mutations, two of which were associated with biallelic IGF2 expression and normal H19 and KCNQ1OT1 imprinting. One patient demonstrated phenotypic expression of paternally transmitted mutation in this maternally expressed gene, a second proband is the child of one of a pair of monozygotic twin females who carry the mutation de novo, and a third patient exhibited unusual skeletal changes more commonly found in other overgrowth syndromes. When considered with other studies published to date, this work reveals the frequency of CDKN1C mutations in BWS to be only 4.9%. This is the first report of an analysis of the imprinting status of genes in the 11p15 region where CDKN1C mutations were associated with loss of IGF2 imprinting and maintenance of H19 and KCNQ1OT1 imprinting.     

Heterozygous germline mutations in the p53 homolog p63 are the cause of EEC syndrome.

EEC syndrome is an autosomal dominant disorder characterized by ectrodactyly, ectodermal dysplasia, and facial clefts. We have mapped the genetic defect in several EEC syndrome families to a region of chromosome 3q27 previously implicated in the EEC-like disorder, limb mammary syndrome (LMS). Analysis of the p63 gene, a homolog of p53 located in the critical LMS/EEC interval, revealed heterozygous mutations in nine unrelated EEC families. Eight mutations result in amino acid substitutions that are predicted to abolish the DNA binding capacity of p63. The ninth is a frameshift mutation that affects the p63alpha, but not p63beta and p63gamma isotypes. Transactivation studies with these mutant p63 isotypes provide a molecular explanation for the dominant character of p63 mutations in EEC syndrome.     

Expression of p57<Superscript>KIP2</Superscript> in infantile hemangioma

Summary Aim: To compare the expression of p57 as indirect marker of genomic imprinting of CDKN1C in a series of infantile hemangiomas (IH) of patients with and without Beckwith–Wiedemann syndrome. Materials and methods: Cases of mammary, salivary gland, liver (one each), and placental (2 cases) capillary hemangiomas all with histological features akin to IH as well as typical examples of cutaneous (8 cases) IH were analyzed by immunohistochemistry with antibody against p57^KIP2. This protein is the product of CDKN1C an imprinted, maternally expressed gene. The liver hemangioma and both chorioangiomas were from patients with Beckwith–Wiedemann syndrome. Positive and negative controls included normal placental tissue and complete hydatidiform mole, respectively. Positive staining was localized to nuclei. Results: Endothelial cells from the skin, breast and salivary gland hemangiomas were p57^KIP2 positive while chorioangiomas and liver IH presenting in patients with Beckwith–Wiedemann syndrome were negative. Controls reacted appropriately. Conclusions: Endothelial cells of IH not associated with BWS normally express p57^KIP2 while chorioangiomas and IH of the liver associated with BWS do not. These results suggest that the BWS IH may result from dysregulation of the cell cycle.     

MECP2 mutations in sporadic cases of Rett syndrome are almost exclusively of paternal origin

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder that apparently is lethal in male embryos. RTT almost exclusively affects female offspring and, in 99.5% of all cases, is sporadic and due to de novo mutations in the MECP2 gene. Familial cases of RTT are rare and are due to X-chromosomal inheritance from a carrier mother. We analyzed the parental origin of MECP2 mutations in sporadic cases of RTT, by analysis of linkage between the mutation in the MECP2 gene and intronic polymorphisms in 27 families with 15 different mutations, and we found a high predominance of mutations of paternal origin in 26 of 27 cases (P<.001). The paternal origin was independent of type of mutation and was found for single-base exchanges as well as for deletions. Parents were not of especially advanced age. We conclude that de novo mutations in RTT occur almost exclusively on the paternally derived X chromosome and that this is most probably the cause for the high female:male ratio observed in patients with RTT. Affected males recently have been described in a few cases of familial inheritance. Identification of the parental origin may be useful to distinguish between the sporadic form of RTT and a potentially familial form. This distinction will allow geneticists to offer more-specific counseling and discriminate between higher (maternal origin) and lower (paternal origin) recurrence risk.     

Alterations of H19 imprinting and IGF2 replication timing are infrequent in Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is an overgrowth disorder resulting from dysregulation of multiple imprinted genes through a variety of distinct mechanisms. A frequent alteration in BWS involves changes in the imprinting status of the coordinately regulated IGF2 and H19 genes on 11p15. Patients have been categorized according to alterations in the imprinted expression, allele-specific methylation, and regional replication timing of these genes. In this work, IGF2/H19 expression, H19 DNA methylation, and IGF2 regional replication timing were studied in nine karyotypically normal BWS fibroblasts and two BWS patients with maternally inherited 11p15 chromosomal rearrangements. Informative patients (9/9) maintained normal monoallelic H19 expression/methylation, despite biallelic IGF2 expression in 6/9. Replication timing studies revealed no changes in the pattern of asynchronous replication timing for both a patient with biallelic IGF2 expression and a patient carrying an 11p15 inversion. In contrast, a patient with a chromosome 11;22 translocation and normal H19 expression/methylation exhibited partial loss of asynchrony and a shift toward earlier replication times. These results indicate that in BWS, (1) H19 imprinting alterations are less frequent than previously estimated, (2) IGF2 imprinting and H19 imprinting are not necessarily coordinated, and (3) alterations in regional replication timing are generally not correlated with either chromosomal rearrangements or the imprinting status of IGF2 and H19.     

p53 mutations are not selected for in simian virus 40 T-antigen-induced tumors from transgenic mice.

Many diverse tumors contain cells that select for mutations at the p53 gene locus. This appears to be the case because the p53 gene product can act as a negative regulator of cell division or a tumor suppressor. These mutations then eliminate this activity of the p53 gene product. The simian virus 40 (SV40) large T antigen binds to p53 and acts as an oncogene to promote cellular transformation and initiate tumors. If the binding of T antigen to the p53 protein inactivated its tumor suppressor activity, there would be no selection pressure for p53 mutants to appear in tumors. To test this idea, transgenic mice that carried and expressed the SV40 large T-antigen gene were created. Expression of the T antigen was directed to the liver, using the albumin promoter, and the choroid plexus, using the SV40 enhancer-promoter. A large number of papillomas (indicated in parentheses) of the choroid plexus (14), hepatocellular carcinomas (5), liver adenomas (10), and tumors of clear-cell foci (5) were examined for mutant and wild-type p53 genes and gene products. In all cases, the tumor extracts contained readily detectable T-antigen-p53 protein complexes. A monoclonal antibody specifically recognizing the wild-type p53 protein (PAb246) reacted with p53 in every tumor extract. A monoclonal antibody specifically recognizing mutant forms of the p53 protein (PAb240) failed to detect p53 antigens in these extracts. Finally, p53 partial cDNAs were sequenced across the regions of common mutations in this gene, and in every case only the wild-type sequence was detected. These results strongly support the hypothesis that T antigen inactivates the wild-type p53 tumor-suppressing activity and there is no need to select for mutations at the p53 locus.     

The multiple roles of the cyclin-dependent kinase inhibitory protein p57(KIP2) in cerebral cortical neurogenesis

The members of the CIP/KIP family of cyclin-dependent kinase (CDK) inhibitory proteins (CKIs), including p57(KIP2), p27(KIP1), and p21(CIP1), block the progression of the cell cycle by binding and inhibiting cyclin/CDK complexes of the G1 phase. In addition to this well-characterized function, p57(KIP2) and p27(KIP1) have been shown to participate in an increasing number of other important cellular processes including cell fate and differentiation, cell motility and migration, and cell death/survival, both in peripheral and central nervous systems. Increasing evidence over the past few years has characterized the functions of the newest CIP/KIP member p57(KIP2) in orchestrating cell proliferation, differentiation, and migration during neurogenesis. Here, we focus our discussion on the multiple roles played by p57(KIP2) during cortical development, making comparisons to p27(KIP1) as well as the INK4 family of CKIs.     

Activating FGFR3 mutations cause mild hyperplasia in human skin,but are insufficient to drive benign or malignant skin tumors

Fibroblast growth factor receptor 3 (FGFR3) activating mutations are drivers of malignancy in several human tissues, including bladder, lung, cervix, and blood. However, in skin, these mutations are associated predominantly with benign, common epidermal growths called seborrheic keratoses (SKs). How epidermis resists FGFR3 mediated transformation is unclear, but previous studies have suggested that FGFR3 activation in skin keratinocytes may serve a tumor-suppressive role by driving differentiation and antagonizing Ras signaling. To define the role of FGFR3 in human normal and neoplastic epidermis, and to directly test the hypothesis that FGFR3 antagonizes Ras, we engineered human skin grafts in vivo with mutant active FGFR3 or shRNA FGFR3 knockdown. We show that FGFR3 active mutants drive mild hyperproliferation, but are insufficient to support benign or malignant tumorigenesis, either alone, or in combination with G₁–S checkpoint release. This suggests that additional cell-intrinsic or stromal cues are required for formation of benign SKs with FGFR3 mutations. Further, FGFR3 activation does not alter the growth kinetics or differentiation status of engineered human epidermal SCCs driven by Ras, and FGFR3 protein itself is dispensable for Ras-driven SCC. To extend these findings to patients, we examined a uniquely informative human tumor in which SCC developed in continuity with a SK, raising the hypothesis that one of the tumors evolved from the other. However, mutational analysis from each tumor indicates that the overlapping SK and SCC evolved independently and supports our conclusion that FGFR3 activation is insufficient to drive SCC.     

IDH1 and IDH2 mutations are frequent in Chinese patients with acute myeloid leukemia but rare in other types of hematological disorders

Frequent mutations in the isocitrate dehydrogenase 1 and 2 genes (IDH1 and IDH2) have been identified in gliomas and acute myeloid leukemia (AML). Our aim is to assess whether IDH mutations were presented in Chinese patients with various hematological disorders. In this study, we screened the IDH1 and IDH2 mutations in a cohort of 456 Chinese patients with various hematological malignancies and disorders. We found three missense (p.R132C, p.R132G, and p.I99M; occurred in five patients) and one silent mutation (c.315C>T; occurred in two patients) in the IDH1 gene and two missense mutations (p.R140Q and p.R172K; occurred in four AML patients) and one silent mutation (c.435G>A) in the IDH2 gene. Except for one non-Hodgkin lymphoma (NHL) patient harboring IDH1 mutation p.R132C, all IDH1 and IDH2 missense mutations were observed in patients with AML. Intriguingly, the IDH2 mutation p.R140Q and novel IDH1 mutation p.I99M co-occurred in a 75-year-old patient with AML developed from myelodysplastic syndromes (MDS). The frequency of IDH1 and IDH2 missense mutations in Chinese AML patients reached 5.9% and 8.3%, respectively. Our results supported the recent findings that IDH gene mutations were common in AML. Conversely, IDH mutations were rather rare in Chinese patients with other types of hematological disorders.     

Identification and analysis of genes present in Leptospira interrogans serovar lai but absent in L. biflexa serovar monvalerio

Genes present in virulent bacterial strains but absent in avirulent close relatives can be of great biologic and clinical interest. This project aimed to identify strain specific DNA sequences of Leptospira interrogens serovar lai, which is absent in the saprophytic L. biflexa serovar monvalerio, via suppression subtractive hybridization with the former as the tester while the latter as the driver. The mixture of PCR amplified DNA fragments from two subtractive hybridization experiments were cloned into pMD 18-T vector and the positive clones were identified by dot blotting against the chromosome DNA of the two strains individually. After DNA sequencing and analysis, the distribution of these genomic fragment sequences in a panel of pathogenic and nonpathogenic leptospires was investigated employing dot blot analysis. Among the 188 positive clones randomly chosen, 24 contained the tester strain specific genomic regions, of which, 5 were non-coding fragments while the others contained 23 distinct protein coding sequences. Besides 9 genes encoding functional proteins, 12 genes encode unknown proteins and the rest two genes encode proteins with recognizable domain structures, one for a putative leucine-rich repeats (LRR) family protein while the other as an outer-membrane protein. Our experiment results indicated that suppression subtractive hybridization is effective for screening specific DNA sequences between two leptospiral strains, and some of these sequences might be responsible for virulence determination. Further analysis of these DNA sequences will provide important information on the pathogenesis of Leptospira.