Effects of dietary active soybean trypsin inhibitors on pancreatic weights, histology and expression of STAT3 and receptors for androgen and estrogen in different tissues of rats

Our previous study showed that soy milks could contain high levels of active soybean trypsin inhibitors (SBTI) if they were not properly processed. This study investigated the effects of consuming active SBTI on pancreatic weights, histology, trypsinogen production and expression of STAT3, receptors for androgen (AR) and estrogen (ER) in pancreas, liver and uterus of rats. Weanling Sprague-Dawley rats were randomly divided into 3 groups (8 females and 8 males/group) and fed diets containing either 20% casein protein (Casein) or 20% soy protein (SP) in the presence of high (1.42 BAEE unit/µg, SP + SBTI) or low (0.2 BAEE unit/µg, SP-SBTI) levels of active SBTI for 8 weeks. Ingestion of SP + SBTI diet markedly increased pancreatic weights and trypsinogen content (p < 0.01), and caused acinar cell hypertrophy, and reduced pancreatic STAT3, p-STAT3, AR and ERβ content, and increased uterine ERα and ERβ compared to the Casein or SP-SBTI diets (p < 0.05). The two SP-containing diets lowered hepatic STAT3, p-STAT3, and pancreatic ERα, and increased hepatic ERα and ERβ content in the female rats compared to the Casein diet (p < 0.05). This study demonstrated for the first time that consumption of high level of active SBTI not only increased pancreatic weights and acinar cell secretions, but also attenuated the expression of pancreatic STAT3, p-STAT3, AR, and ERβ proteins in both sexes and increased uterine ERα and ERβ content, and that dietary soy protein affected hepatic STAT3, p-STAT3, ERα and ERβ in a gender-dependent manner.

Near edge X-ray absorption mass spectrometry of gas phase proteins: the influence of protein size

The response of gas-phase proteins upon soft X-ray absorption depends strongly on the proteins size.

Flow cytometry and FISH to investigate allele-specific replication timing and homologous association of imprinted chromosomes

Chromosome replication banding studies show that homologous regions on a pair of autosomes generally replicate at the same time in S phase (1). Izumikawa et al. first observed that this was not the case for the imprinted chromosomal region 15q11-q13 (2). This observation has been confirmed in other replication banding studies (3) as well by the fluorescence in situ hybridization (FISH) replication assay (4-9). The latter technique has also been used to observe DNA replication asynchrony in association with allelic inactivation of genes such as those encoding olfactory receptors and the cytokine, interleukin 2 (10,11). The latter genes are not imprinted but display random silencing of an allele in individual cells. In imprinted regions, DNA replication was generally observed to occur earlier on the paternal homologue (5,6,9,12,13). The patterns of allele-specific replication in the cells of Prader- Willi (PWS) and Angelman syndrome (AS) patients, however, have generally been synchronous (5,6,14). Furthermore, an investigation of the kinetics of allele-specific replication timing in the GABRB3/A5 cluster on 15q11-13 revealed that cells from PWS and AS have lost the strict replication timing observed on the parental chromosomes of normal cells (12). These results suggested the requirement of a biparental contribution for the regulation of replication asynchrony and lead to the hypothesis that allelic cross-talk, perhaps via pairing of homologous chromosomes, might play a role in the imprinting process.

[Structured treatment interruption in HIV-infected adolescents]

Structured treatment interruption in HIV is now being debated. There are 2 cases in which it may be discussed: when the initial treatment was started early and when there is no compliance to treatment [Yeni P, et al. Les nouvelles recommandations de prise en charge des personnes infectées par le VIH 2006. Paris: Flammarion médecine-sciences; 2006]. Noncompliant behavior is one of the characteristics of chronic illness during adolescence. In HIV infection, however, the prognosis is negatively influenced because the resulting resistance to the antiretroviral therapy can further reduce therapeutic options. Therefore, it is important in such a critical period to consider both what is consciously and unconsciously at stake and what responsible action could be taken when a specialist is faced with spontaneous (unplanned) treatment interruption. We report here examples of follow-up care, interruption, and resumption of treatment in 4 female adolescents.

[Turicella otitidis infection: otitis media complicated by mastoiditis]

Turicella otitidis is a nonfermentative, Gram-positive bacillus, which is almost exclusively isolated from the ear. Few cases of infection caused by T. otitidis have been reported in the literature, but the pathogenic potential of this little-known bacterium remains controversial, particularly in acute and chronic otitis media.

CLINICAL OBSERVATIONS

A retrospective study of T. otitidis isolated in the University Hospital of Montpellier in 2004 found T. otitidis in 13 patients. Among them, a 3-year-old girl had presented with acute and perforated otitis media and mastoiditis caused by T. otitidis, thereby confirming the pathogenic effect of this bacterium.

CONCLUSION

T. otitidis is relatively frequently isolated from middle ear samples in healthy patients. However, T. otitidis has been implicated in serious cases of infection and should be considered an opportunistic pathogen. Its clinical significance can be difficult to establish and each case should be carefully interpreted. From a bacteriological point of view, T. otitidis should be precisely identified to obtain more information regarding its role in clinical pathology.

Molecular epigenetics of Angelman syndrome

Angelman syndrome (AS) is a neurogenetic disorder characterized by severe mental retardation, ataxia, seizures, EEG abnormalities and bouts of inappropriate laughter. AS individuals fail to inherit a normal active maternal copy of ubiquitin protein ligase E3A (UBE3A). UBE3A is subject to genomic imprinting, with predominant transcription of the maternal allele in brain. The known genetic causes of AS are maternal deletion of chromosome 15q11-q13, paternal chromosome 15 uniparental disomy, UBE3A mutation and an abnormality of the imprinting process, termed imprinting defect. There remain major questions concerning the molecular pathogenesis of AS, including: 1) the mechanisms underlying the imprinting defect class of AS, 2) the identity of proteins targeted by UBE3A, 3) the role of a noncoding antisense transcript in regulating UBE3A imprinting and 4) the contribution of other genes such as methyl-binding CpG-binding protein 2 and gamma-aminobutyric acid A receptor, subunit beta3 to the AS phenotype.

[Eruptive pseudoangiomatosis in infant and newborns]

INTRODUCTION

Eruptive pseudoangiomatosis was first described in children in the form of an acute non-pruritic macular or papular rash that fades on application of a glass test and resolves within several days. Viral aetiology is suspected but has never been demonstrated to date.

OBSERVATIONS

We discuss seven cases of infants presenting this disease: 5 boys and 2 girls aged 8 days to 16 months. The rash presented typical clinical features in all cases and affected the face and limbs in 6 of the 7 subjects. In one child, involvement of the face and back was observed with sparing of the limbs. The rash occurred after an episode of rhinolaryngeal infection in 3 cases and after gastrointestinal infection in 1 case. Spontaneous resolution was seen within 3 to 10 days in 6 patients although a longer course lasting over 9 months was observed in one infant. In another patient, the rash appeared after surgery for mesoblastic nephroma. In one child, a similar rash was seen in both parents. Screening for infectious agents was negative for the two children from whom samples were obtained.

DISCUSSION

This series of paediatric cases of eruptive pseudoangiomatosis is characterised by the very young age of one of the children, coexistence of the condition with a renal tumour in another child, the familial nature of the rash in a third child and unusually long disease duration in the final child. However, this series did not allow identification of the causative infectious agent or agents. Probably, as with other syndromes such as Giannotti-Crosti syndrome or "gloves and socks" syndrome, eruptive pseudoangiomatosis forms a clinical picture common to a non-specific viral infection.

[Quality of life in HIV-infected children and adolescents under highly active antiretroviral therapy: change over time, effects of age and familial context]

OBJECTIVE

To evaluate Quality of life (QoL) of HIV-infected children under highly active antiretroviral therapies, and its change over 18 months.

MATERIALS AND METHODS

QoL was evaluated by self-administred questionnaires (french versions of AUQUEI, OK-ado, and compilation of both) in 23 young living with HIV/AIDS (6-15 yrs), under antiretroviral multitherapies, and re-evaluated 18 months later in 19 of them.

RESULTS

At baseline, QoL in HIV-infected children-adolescents was relatively good. The answers given to each items and the mean score from infected children were similar to those obtained in uninfected healthy children. Moreover, infected adolescents distinguished definitly from healthy adolescents, describing higher QoL. The mean satisfaction score from the whole group decreased between M0 and M18 (mainly in the youngests), and mainly concerned 3 fields (self-esteem, health and school) while their somatic health remained stable or improved. An effect of the familial context was also observed for these 3 fields.

CONCLUSION

The progressive decline of QoL in HIV-infected children, and the surprising high and steady level of satisfaction over-time provided by the adolescents, underlined the frailty of this population and the need for a psychologic management associated to the medical follow-up. Such a multidisciplinary approach should take into account the preoccupations and difficulties of each age-class, those linked to the diagnosis itself, and to the familial or scolar contexts, in order to preserve QoL of this pediatric population, as far as possible, in a long term.

Les pleurésies purulentes de l'enfant: Expérience montpelliéraine

OBJECTIVES AND METHOD

To assess the management of pleural empyema in pediatric from a medical and surgical experience and a review of the literature.

STUDY

Fifty-eight cases were reviewed from January 98 to December 2003. 62.6% have already received antibiotherapy. Forty-three percent of cases were less than three years old. Initial cultures identified Streptococcus pneumoniae in 39%, Streptococcus pyogenes in 5.6%, Mycoplasma pneumoniae and Staphylococcus aureus in only one case and were negative in 47%. A primitive or second-line thoracoscopy were used for drainage in two-third of the cases and mainly 6.95 days after admission. Located pleural empyema and major collected volume were the main indications for thoracoscopy. Three cases have been converted into open thoracotomy. One death occurred in an immunocompromised child. All patients were well at last follow-up.

DISCUSSION

The frequency of parapneumonic empyema has increased since ten years. Progress of echography and endoscopy changed their management. Antibiotics have to be effective against pneumococcal infection. Chest tube drainage is necessary to assure the lung reexpansion in case of fibropurulent collection. The difficulty is to optimise the time of video-assisted thoracoscopy (VAT) using predictive criteria as loculations and pneumatoceles. VAT allowed the aspiration of pleural fluid and removing of fibrinous loculations. Moreover VAT achieved optimal adhesiolysis and the irrigation or decortication of the pleural cavity. VAT minimized duration of stay, of chest tube drainage and the indications of thoracotomy.

[Group B streptococcal infection with 2 recurrences in a newborn]

Group B III streptococcus (GBS) is a predominant pathogen in neonates in France. Relapse is rare and two successive relapses are exceptional: only three cases have been yet reported.

CASE REPORT

A newborn infant of 18 days of age presented a first episode of invasive group B III streptococcal infection with meningitis and ventriculitis. At 53 days of age, a second episode with bacteriemia and parotidis appeared. At 63 days of age, she presented a third episode with meningitis. Genome analysis of the three bacterial strains isolated during the three episodes showed the same clonal origin.

COMMENTS

We discuss the incidence of the treatment, the eventual presence of a penicillin-tolerant GBS, the possible relapse or recurrence of the pathogen and the role of the relative immunodeficiency in infant.

Identification and characterization of three members of a novel subclass of protocadherins

Protocadherins are members of a nonclassic subfamily of calcium-dependent cell-cell adhesion molecules in the cadherin superfamily. Although the extracellular domains have several common structural features, there is no extensive homology between the cytoplasmic domains of protocadherin subfamily members. We have identified a new subclass of protocadherins based on a shared and highly conserved 17-amino-acid cytoplasmic motif. The subclass currently consists of 18 protocadherin members. Two of these, PCDH18 and PCDH19, are novel protocadherins and a third is the human orthologue of mouse Pcdh10. All three genes encode six ectodomain repeats with cadherin-like attributes and, consistent with the structural characteristics of protocadherins, a large first exon encodes the extracellular domain of each gene.

Identification of brain-specific and imprinted small nucleolar RNA genes exhibiting an unusual genomic organization

We have identified three C/D-box small nucleolar RNAs (snoRNAs) and one H/ACA-box snoRNA in mouse and human. In mice, all four snoRNAs (MBII-13, MBII-52, MBII-85, and MBI-36) are exclusively expressed in the brain, unlike all other known snoRNAs. Two of the human RNA orthologues (HBII-52 and HBI-36) share this expression pattern, and the remainder, HBII-13 and HBII-85, are prevalently expressed in that tissue. In mice and humans, the brain-specific H/ACA box snoRNA (MBI-36 and HBI-36, respectively) is intron-encoded in the brain-specific serotonin 2C receptor gene. The three human C/D box snoRNAs map to chromosome 15q11-q13, within a region implicated in the Prader-Willi syndrome (PWS), which is a neurogenetic disease resulting from a deficiency of paternal gene expression. Unlike other C/D box snoRNAs, two snoRNAs, HBII-52 and HBII-85, are encoded in a tandemly repeated array of 47 or 24 units, respectively. In mouse the homologue of HBII-52 is processed from intronic portions of the tandem repeats. Interestingly, these snoRNAs were absent from the cortex of a patient with PWS and from a PWS mouse model, demonstrating their paternal imprinting status and pointing to their potential role in the etiology of PWS. Despite displaying hallmarks of the two families of ubiquitous snoRNAs that guide 2'-O-ribose methylation and pseudouridylation of rRNA, respectively, they lack any telltale rRNA complementarity. Instead, brain-specific C/D box snoRNA HBII-52 has an 18-nt phylogenetically conserved complementarity to a critical segment of serotonin 2C receptor mRNA, pointing to a potential role in the processing of this mRNA.

The human MAGEL2 gene and its mouse homologue are paternally expressed and mapped to the Prader-Willi region

Prader-Willi syndrome (PWS) is a complex neurogenetic disorder. The phenotype is likely to be a contiguous gene syndrome involving genes which are paternally expressed only, located in the human 15q11-q13 region. Four mouse models of PWS have been reported but these do not definitively allow the delineation of the critical region and the associated genes involved in the aetiology of PWS. Moreover, targeted mutagenesis of mouse homologues of the human candidate PWS genes does not appear to result in any of the features of PWS. Therefore, the isolation of new genes in this region remains crucial for a better understanding of the molecular basis of PWS. In this manuscript, we report the characterization of MAGEL2 and its mouse homologue Magel2. These are located in the human 15q11-q13 and mouse 7C regions, in close proximity to NDN / Ndn. By northern blot analysis we did not detect any expression of MAGEL2 / Magel2 but by RT-PCR analysis, specific expression was detected in fetal and adult brain and in placenta. Both genes are intronless with tandem direct repeat sequences contained within a CpG island in the 5'-untranscribed region. The transcripts encode putative proteins that are homologous to the MAGE proteins and NDN. Moreover, MAGEL2 / Magel2 are expressed only from the paternal allele in brain, suggesting a potential role in the aetiology of PWS and its mouse model, respectively.

Replication timing of CD4 and CD8 in single-positive peripheral blood lymphocytes

The regulatory events leading to the mutually exclusive expression of CD4 and CD8 on peripheral lymphocytes are not fully understood. In particular, the association between DNA replication timing and transcriptional activity of these genes has not been previously investigated. Here, the replication kinetics of the CD4 and CD8 loci in mature single-positive T-cell populations have been examined using a novel approach to the separation of CD4(+) or CD8(+) lymphocytes into discrete cell cycle fractions and a competitive PCR replication timing assay. While the timing of replication of each of these loci is independent of their expression in mature CD4 or CD8 single positive T-cells, the replication of CD8, but not of CD4, shifts to a later time in S phase in transcriptionally silent HS68 fibroblast cells. These findings suggest that changes in DNA replication timing are associated with the developmentally regulated but not with the tissue-specific expression of CD4 and CD8.

Parental imprinting and Angelman syndrome

Angelman syndrome is an inherited disorder that includes severe mental retardation and epilepsy. Patients have no speech, puppet-like gait with jerky movements, hyperactivity, disturbed sleep, bouts of inappropriate laughter, a pronounced jaw, and widely spaced teeth. The syndrome results from deletion or mutation within maternal chromosome 15q11-q13. Considerable evidence suggests that the gene or genes responsible for Angelman syndrome are expressed only from the maternal chromosome 15, a situation known as parental imprinting. This epigenetic marking of certain regions of the parental genomes is characterized by parent-of-origin-specific allelic DNA methylation, allele-specific DNA replication timing, and physical pairing of the two chromosome 15 homologues. Imprinting is important for normal development, and its disregulation causes several human disorders. The epilepsy of Angelman syndrome has been studied and indicates a rather typical electroencephalographic abnormality with slowing and notched wave and spikes. Various types of seizures occur, usually including myoclonus and atypical absence. Variable severity among patients suggests potential molecular diversity in the genetic mechanism, possibly the involvement of more than one gene. Angelman syndrome can arise from the following molecular genetic defects: a deletion in 15q11-q13 that covers the Angelman gene or genes, mutations that alter imprinting, and paternal uni-parental disomy for the region. Another 20% or so of patients with clinical symptoms of Angelman syndrome have none of these three defects but are believed to have mutations in one or more genes in the region, and this may be familial. The UBE3A gene, which codes for the enzyme ubiquitin protein ligase involved in protein degradation and processing, has been found to be mutated in many but not all of patients with Angelman syndrome and can be considered a major Angelman candidate gene. Other potential candidate genes in the region include a cluster of three GABAA receptor subunits, which are involved in inhibitory synaptic transmission in the brain. The GABRB3 gene, which codes for the beta 3 subunit, is deleted in most persons with Angelman syndrome. The absence of this gene in mice causes craniofacial abnormalities and neurologic impairment with seizures. The exact role of UBE3A and GABRB3 in the syndrome and their imprinting status are under investigation.

Phenotype-genotype correlation in 20 deletion and 20 non-deletion Angelman syndrome patients

Angelman syndrome (AS) is a neurodevelopmental disorder caused by the absence of a maternal contribution to chromosome 15q11-q13. There are four classes of AS according to molecular or cytogenetic status: maternal microdeletion of 15q11-q13 (approximately 70% of AS patients); uniparental disomy (UPD); defects in a putative imprinting centre (IM); the fourth includes 20-30% of AS individuals with biparental inheritance and a normal pattern of allelic methylation in 15q11-q13. Mutations of UBE3A have recently been identified as causing AS in the latter group. Few studies have investigated the phenotypic differences between these classes. We compared 20 non-deletion to 20 age-matched deletion patients and found significant phenotypic differences between the two groups. The more severe phenotype in the deletion group may suggest a contiguous gene syndrome.

An 18q- syndrome breakpoint resides between the duplicated serpins SCCA1 and SCCA2 and arises via a cryptic rearrangement with satellite III DNA

The 18q-syndrome is representative of a group of terminal deficiency or macrodeletion syndromes characterized by mental retardation and congenital malformations. To gain insight into the mechanism of chromosomal loss and stabilization in these disorders, we cloned a putative terminal deletion breakpoint from an 18q-syndrome patient. The 18q21.3 breakpoint occurred between two nearly identical serine protease inhibitor (serpin) genes, SCCA1 and SCCA2. Although cytogenetic studies suggested that this chromosomal aberration was formed by a simple terminal deletion, DNA sequence analysis, pulsed-field gel electrophoresis and fluorescence in situ hybridization showed that the breakpoint was contiguous with a 35 bp filler sequence followed by a satellite III DNA-containing telomeric fragment of 475-1000 kb. This type of satellite III DNA sequence was not detected on the normal chromosome 18, but was highly homologous with types of satellite III DNA sequences normally located on the short arms (p11) of the acrocentric chromosomes and other heterochromatic regions. This DNA sequence analysis suggested that the terminal deficiency in this 18q-syndrome patient arose via illegitimate (non-homologous) recombination. Moreover, these data raise the possibility that a subset of chromosomal aberrations appearing cytogenetically and molecularly as simple terminal truncations or deletions are caused by small (<1000 kb) cryptic rearrangements.

Complications of abortion performed under local anesthesia

OBJECTIVE

To assess the incidence of complications of abortion performed under local anesthesia.

DESIGN

Prospective study.

SETTING

A family planning center in the Paris area.

POPULATION

Eight hundred and fifty-eight women admitted for abortion under local anesthesia.

MAIN OUTCOME MEASURES

Incidence of immediate (the day of vacuum aspiration) and delayed complications (at the follow-up visit 2 weeks after the procedure).

RESULTS

Among the 858 women who underwent vacuum aspiration, 683 (80%) attended the follow-up visit 2 weeks after the procedure. Fifty-nine percent of the 858 women had not had a previous abortion, 25% had had one, and 16% had had two or more. The average duration of amenorrhea was 8.6 weeks (19% at 6 or 7 weeks, 67% between 8 and 10 weeks, and 14% after 10 weeks). The overall complication rate was 3.4% (23/683) (95% CI=2.0-4.8%). The incidence of immediate complications was 1.7% (15/858) (0.8-2.6%) and that of delayed complications 1.2% (8/683) (0.4-2.0%).

CONCLUSION

This study confirms the safety and efficacy of abortion by vacuum aspiration under local anesthesia.

Characterization of two novel protocadherins (PCDH8 and PCDH9) localized on human chromosome 13 and mouse chromosome 14

The protocadherins are a subfamily of the calcium-dependent cell-cell adhesion and recognition proteins of the cadherin superfamily. In this study we describe the isolation and characterization of two novel protocadherins, PCDH8 and PCDH9, that constitute a new linkage group on human chromosome 13 and mouse chromosome 14. Like other protocadherins both genes are predominantly expressed in brain, but PCDH9 is also expressed in a broader variety of tissues, and the expression patterns appear to be developmentally regulated. We have determined the genomic organization of PCDH8, which differs significantly from that of the other cadherin subfamilies. In contrast to the classical and desmosomal cadherins, which in general consist of 15-17 exons and share a remarkable degree of conservation in intron position, PCDH8 consists of only three exons and lacks introns in the extracellular domain. The first exon encodes the extracellular domain, the transmembrane region, and part of the cytoplasmic tail. The second exon encodes the remainder of the cytoplasmic region and is partially untranslated. The differences in the genomic structure of cadherin subfamilies will be discussed in the context of the evolution of the cadherin superfamily.

Angelman syndrome: how many genes to remain silent?

The clinical features of Angelman syndrome (AS) include microcephaly, severe mental retardation, "puppet-like" ataxic gait with jerky arm movements, hyperactivity, bouts of inappropriate laughter, EEG abnormalities, and seizures. The frequency of occurrence of AS is in the range of 1/10,000 to 1/20,000 births. The AS locus maps to the imprinted chromosome 15q11-q13 region and the disease is caused by the absence of a normal maternal contribution to this region. The genetic complexity of AS is revealed by the existence of at least four molecular classes. A candidate AS gene, ubiquitin protein ligase 3A (UBE3A/E6-AP), has been identified, and mutations of this gene have been detected in several cases of AS. Moreover, UBE3A is expressed predominantly from the maternal allele in brain, strongly supporting its causative role in AS. However, there is evidence to suggest that, in addition to UBE3A, another gene(s) may be involved either directly in AS and/or indirectly by regulating UBE3A expression.

A large polymorphic repeat in the pericentromeric region of human chromosome 15q contains three partial gene duplications

We report the identification of a partial duplication of GABRA5 , a gene within the imprinted 15q11-q13 region. The duplicated locus maps to the pericentromeric region of 15q, proximal to the large deletions associated with Angelman and Prader-Willi syndromes. We also observed variation in the number of copies of this locus in different individuals, indicating that the duplication is part of a variable repeat. Investigation of the duplication in individuals with a normal karyotype revealed between one and four copies of the repeat on each chromosome 15, whereas from eight to 20 copies were found in individuals possessing a cytogenetically detectable elongation of the 15q region. The variable region is roughly 1 Mb in size and contains two other non-processed duplications, the immunoglobulin heavy chain (IgH) D segment gene and the neurofibromatosis type 1 (NF1) gene. One unit of the pericentromeric repeat is thus composed of duplications of genes from different chromosomal regions. Moreover, we have found replication asynchrony across the GABRA5 duplication, suggesting for the first time that the imprinted part of chromosome 15q extends proximal of the region commonly deleted in Angelman and Prader-Willi syndromes.

Sporadic imprinting defects in Prader-Willi syndrome and Angelman syndrome: implications for imprint-switch models, genetic counseling, and prenatal diagnosis

The Prader-Willi syndrome (PWS) and the Angelman syndrome (AS) are caused by the loss of function of imprinted genes in proximal 15q. In approximately 2%-4% of patients, this loss of function is due to an imprinting defect. In some cases, the imprinting defect is the result of a parental imprint-switch failure caused by a microdeletion of the imprinting center (IC). Here we describe the molecular analysis of 13 PWS patients and 17 AS patients who have an imprinting defect but no IC deletion. Heteroduplex and partial sequence analysis did not reveal any point mutations of the known IC elements, either. Interestingly, all of these patients represent sporadic cases, and some share the paternal (PWS) or the maternal (AS) 15q11-q13 haplotype with an unaffected sib. In each of five PWS patients informative for the grandparental origin of the incorrectly imprinted chromosome region and four cases described elsewhere, the maternally imprinted paternal chromosome region was inherited from the paternal grandmother. This suggests that the grandmaternal imprint was not erased in the father's germ line. In seven informative AS patients reported here and in three previously reported patients, the paternally imprinted maternal chromosome region was inherited from either the maternal grandfather or the maternal grandmother. The latter finding is not compatible with an imprint-switch failure, but it suggests that a paternal imprint developed either in the maternal germ line or postzygotically. We conclude (1) that the incorrect imprint in non-IC-deletion cases is the result of a spontaneous prezygotic or postzygotic error, (2) that these cases have a low recurrence risk, and (3) that the paternal imprint may be the default imprint.

Clonal heterogeneity at allelic methylation sites diagnostic for Prader-Willi and Angelman syndromes

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are developmental disorders resulting from the absence of the paternal or maternal contribution to the 15q11-13 region, respectively. Allele-specific methylation at D15S63 (PW71) has routinely been used as a diagnostic indicator of PWS and AS in DNA samples derived from peripheral blood. Extensive variation in allele-specific methylation patterns, however, has been observed at this site in different tissues, but the frequency or mechanism of this variation has remained uncharacterized. Herein, we have investigated the cellular basis of variation in methylation patterns at four sites of allelic methylation near SNRPN by using DNA samples derived from a panel of primary T lymphocyte clones. Interclonal variability was observed at three of these sites, including the diagnostic PW71 site. Changes in allele-specific methylation patterns occurred at a frequency of about one change in 50% of the cells every 22-25 doublings. In contrast, stable allele-specific methylation was observed in these clonal populations at exon 1 of SNRPN and the androgen receptor locus on the inactive X chromosome, suggesting that methylation at some CpG sites is more faithfully maintained than others. Clonal heterogeneity at PW71 was not an artifact of cell culture because the absence of allelic methylation was also observed in about 20% of the alleles in unstimulated peripheral blood. These results demonstrate that variation in allele-specific methylation at PW71 and other sites in the PWS/AS region appear to depend on the clonal complexity of the particular tissue and on the lack of strict maintenance of methylation within clones.

The human necdin gene, NDN, is maternally imprinted and located in the Prader-Willi syndrome chromosomal region

Prader-Willi syndrome (PWS) is a neurogenetic disorder that results from the absence of a normal paternal contribution to the 15q11-13 region. The clinical manifestations of PWS are a transient severe hypotonia in the newborn period, with mental retardation, hypogonadism and obesity observed later in development. Five transcripts with exclusive expression from the paternal allele have been isolated, but none of these has been shown to be involved in PWS. In this study, we report the isolation and characterization of NDN, a new human imprinted gene. NDN is exclusively expressed from the paternal allele in the tissues analysed and is located in the PWS region. It encodes a putative protein homologous to the mouse brain-specific NECDIN protein, NDN; as in mouse, expression in brain is restricted to post-mitotic neurons. NDN displays several characteristics of an imprinted locus, including allelic DNA methylation and asynchronous DNA replication. A complete lack of NDN expression in PWS brain and fibroblasts indicates that the gene is expressed exclusively from the paternal allele in these tissues and suggests a possible role of this new gene in PWS.

High-resolution analysis of DNA replication domain organization across an R/G-band boundary

Establishing how mammalian chromosome replication is regulated and how groups of replication origins are organized into replication bands will significantly increase our understanding of chromosome organization. Replication time bands in mammalian chromosomes show overall congruency with structural R- and G-banding patterns as revealed by different chromosome banding techniques. Thus, chromosome bands reflect variations in the longitudinal structure and function of the chromosome, but little is known about the structural basis of the metaphase chromosome banding pattern. At the microscopic level, both structural R and G bands and replication bands occupy discrete domains along chromosomes, suggesting separation by distinct boundaries. The purpose of this study was to determine replication timing differences encompassing a boundary between differentially replicating chromosomal bands. Using competitive PCR on replicated DNA from flow-sorted cell cycle fractions, we have analyzed the replication timing of markers spanning roughly 5 Mb of human chromosome 13q14.3/q21.1. This is only the second report of high-resolution analysis of replication timing differences across an R/G-band boundary. In contrast to previous work, however, we find that band boundaries are defined by a gradient in replication timing rather than by a sharp boundary separating R and G bands into functionally distinct chromatin compartments. These findings indicate that topographical band boundaries are not defined by specific sequences or structures.