Maternal uniparental disomy 7--review and further delineation of the phenotype

Genetic variation in placental insufficiency: What have we learned over time?

Genetic variation shapes placental development and function, which has long been known to impact fetal growth and pregnancy outcomes such as miscarriage or maternal pre-eclampsia. Early epidemiology studies provided evidence of a strong heritable component to these conditions with both maternal and fetal-placental genetic factors contributing. Subsequently, cytogenetic studies of the placenta and the advent of prenatal diagnosis to detect chromosomal abnormalities provided direct evidence of the importance of spontaneously arising genetic variation in the placenta, such as trisomy and uniparental disomy, drawing inferences that remain relevant to this day. Candidate gene approaches highlighted the role of genetic variation in genes influencing immune interactions at the maternal-fetal interface and angiogenic factors. More recently, the emergence of molecular techniques and in particular high-throughput technologies such as Single-Nucleotide Polymorphism (SNP) arrays, has facilitated the discovery of copy number variation and study of SNP associations with conditions related to placental insufficiency. This review integrates past and more recent knowledge to provide important insights into the role of placental function on fetal and perinatal health, as well as into the mechanisms leading to genetic variation during development.

The Role of Epigenetic Mechanisms in Autoimmune, Neurodegenerative, Cardiovascular, and Imprinting Disorders

Epigenetic mutations like aberrant DNA methylation, histone modifications, or RNA silencing are found in a number of human diseases. This review article discusses the epigenetic mechanisms involved in neurodegenerative disorders, cardiovascular disorders, auto-immune disorder, and genomic imprinting disorders. In addition, emerging epigenetic therapeutic strategies for the treatment of such disorders are presented. Medicinal chemistry campaigns highlighting the efforts of the chemists invested towards the rational design of small molecule inhibitors have also been included. Pleasingly, several classes of epigenetic inhibitors, DNMT, HDAC, BET, HAT, and HMT inhibitors along with RNA based therapies have exhibited the potential to emerge as therapeutics in the longer run. It is quite hopeful that epigenetic modulator-based therapies will advance to clinical stage investigations by leaps and bounds.

Expression of imprinted genes in placenta is associated with infant neurobehavioral development

Genomic imprinting disorders often exhibit delayed neurobehavioral development, suggesting this unique mechanism of epigenetic regulation plays a role in mental and neurological health. While major errors in imprinting have been linked to adverse health outcomes, there has been little research conducted on how moderate variability in imprinted gene expression within a population contributes to differences in neurobehavioral outcomes, particularly at birth. Here, we profiled the expression of 108 known and putative imprinted genes in human placenta samples from 615 infants assessed by the Neonatal Intensive Care Unit (NICU) Network Neurobehavioral Scales (NNNS). Data reduction identified 10 genes (DLX5, DHCR24, VTRNA2-1, PHLDA2, NPAP1, FAM50B, GNAS-AS1, PAX8-AS1, SHANK2, and COPG2IT1) whose expression could distinguish between newborn neurobehavioral profiles derived from the NNNS. Clustering infants based on the expression pattern of these genes identified 2 groups of infants characterized by reduced quality of movement, increased signs of asymmetrical and non-optimal reflexes, and increased odds of demonstrating increased signs of physiologic stress and abstinence. Overall, these results suggest that common variation in placental imprinted gene expression is linked to suboptimal performance on scales of neurological functioning as well as with increased signs of physiologic stress, highlighting the central importance of the control of expression of these genes in the placenta for neurobehavioral development.

Spinal Deformity in Russell-Silver Syndrome

STUDY DESIGN

Cross-sectional analysis.

OBJECTIVES

To evaluate the prevalence of scoliosis and kyphosis in patients with Russell-Silver syndrome (RSS).

SUMMARY OF BACKGROUND DATA

Russell-Silver syndrome was described by Silver and Russell in the 1950s and 1960s and is characterized by body asymmetry and other growth abnormalities. To the authors' knowledge, this is the first study to evaluate the prevalence of scoliosis and kyphosis in patients with Russell Silver Syndrome.

METHODS

The authors performed a cross-sectional analysis of 163 persons, identified through a national RSS foundation, who consented to be included in the study and responded to a general survey questionnaire. Subjects who reported a diagnosis of scoliosis and/or kyphosis were subsequently asked to submit copies of prior spinal radiographs for evaluation at the authors' center. For evaluation of scoliosis and kyphosis on the radiographs, the researchers reviewed posteroanterior and lateral standing radiographs to measure coronal and sagittal Cobb angles.

RESULTS

Of 163 respondents, 24 (14%) reported scoliosis, 5 (3.1%) reported kyphosis, and 6 (3.8%) reported both kyphosis and scoliosis, with average age of diagnosis of 8 years (range, 1-43 years). Of these respondents, 6 reported a history of bracing for scoliosis and/or kyphosis and 3 braced respondents reported having had surgery for scoliosis and/or kyphosis. An additional 3 respondents reported that corrective spinal surgery was "planned for the future."

CONCLUSIONS

Persons with RSS have a high prevalence of spinal deformity (21%) and a significant number of these patients will undergo corrective surgery (6 of 34; 18%).

Uniparentale Disomien und Mosaike

Für die Entstehung von uniparentalen Disomien (UPD) sind verschiedene Mechanismen bekannt, von denen insbesondere der häufigste, der „trisomy rescue“, mit Mosaiken aus einer trisomen Zelllinie und einer disomen 46,XN-Zelllinie mit UPD einhergehen kann. Daher wird diskutiert, ob ein Großteil der UPD schwache oder nichterkannte Mosaike sein könnten. Inwieweit eine trisome Zelllinie den Phänotyp beeinflusst, hängt wahrscheinlich vom Chromosom und v. a. vom prozentualen Anteil im jeweiligen Gewebe ab. Möglicherweise haben die trisomen Zellen mancher UPD-Mosaike sogar einen Selektionsnachteil, sodass sie zumindest postnatal in der Routineanalytik aus Lymphozyten nicht darstellbar sind. Bei Beteiligung eines Chromosoms, für das „Imprinting“-Phänomene bekannt sind, muss die entsprechende Erkrankung berücksichtigt werden. Während die postnatale molekulare Abklärung einer UPD bei Vorliegen einer entsprechenden klinischen Symptomatik und/oder chromosomaler bzw. molekularer Vorbefunde indiziert ist, sind im Rahmen der pränatalen Testung auf UPD und Imprinting-Erkrankungen die Konsequenzen eines positiven Befunds vor der Diagnostik im Rahmen einer genetischen Beratung mit den Eltern zu diskutieren. Die Bedeutung von Mosaiken für die UPD-Diagnostik muss vor dem Hintergrund des beteiligten Chromosoms bzw. der assoziierten Erkrankung, des zugrunde liegenden Entstehungsmechanismus und der verwendeten Methode bewertet werden.

Neonatal Silver-Russell syndrome with maternal uniparental heterodisomy, trisomy 7 mosaicism, and dysplasia of the cerebellum

OBJECTIVES

We report here the unusual association of Silver-Russell syndrome (SRS) and cerebellar dysplasia with trisomy 7 mosaicism and maternal uniparental disomy of chromosome 7 [UPD(7)m].

METHODS

Low-level trisomy 7 mosaicism was diagnosed prenatally on amniocytes, and UPD(7)m was confirmed after birth.

RESULTS

Medical examination at birth showed dysmorphic facial features of SRS. Cytogenetic analysis on several tissues and cells confirmed mosaic trisomy 7. Unusual severe psychomotor retardation, hypotonia, and choreoathetoid movement were noted at 6 months. Brain magnetic resonance imaging showed both cerebellar hypoplasia and dysplasia.

CONCLUSIONS

This unusual association of SRS and dysplasia of the cerebellum might be related to the presence of the trisomy 7 mosaicism on the cerebellum. Our observation strengthens the hypothesis that the phenotype observed in patients with SRS with UPD(7)m might also result from an undetected low level of trisomy 7 mosaicism that could best be revealed by performing cytogenetic investigations.

Molecular and clinical studies in 138 Japanese patients with Silver-Russell syndrome

Background

Recent studies have revealed relative frequency and characteristic phenotype of two major causative factors for Silver-Russell syndrome (SRS), i.e. epimutation of the H19-differentially methylated region (DMR) and uniparental maternal disomy 7 (upd(7)mat), as well as multilocus methylation abnormalities and positive correlation between methylation index and body and placental sizes in H19-DMR epimutation. Furthermore, rare genomic alterations have been found in a few of patients with idiopathic SRS. Here, we performed molecular and clinical findings in 138 Japanese SRS patients, and examined these matters.

Methodology/Principal Findings

We identified H19-DMR epimutation in cases 1–43 (group 1), upd(7)mat in cases 44–52 (group 2), and neither H19-DMR epimutation nor upd(7)mat in cases 53–138 (group 3). Multilocus analysis revealed hyper- or hypomethylated DMRs in 2.4% of examined DMRs in group 1; in particular, an extremely hypomethylated ARHI-DMR was identified in case 13. Oligonucleotide array comparative genomic hybridization identified a ∼3.86 Mb deletion at chromosome 17q24 in case 73. Epigenotype-phenotype analysis revealed that group 1 had more reduced birth length and weight, more preserved birth occipitofrontal circumference (OFC), more frequent body asymmetry and brachydactyly, and less frequent speech delay than group 2. The degree of placental hypoplasia was similar between the two groups. In group 1, the methylation index for the H19-DMR was positively correlated with birth length and weight, present height and weight, and placental weight, but with neither birth nor present OFC.

Conclusions/Significance

The results are grossly consistent with the previously reported data, although the frequency of epimutations is lower in the Japanese SRS patients than in the Western European SRS patients. Furthermore, the results provide useful information regarding placental hypoplasia in SRS, clinical phenotypes of the hypomethylated ARHI-DMR, and underlying causative factors for idiopathic SRS.

IGF-I and IGF Binding Protein-3 Generation Tests and Response to Growth Hormone in Children with Silver-Russell Syndrome

Objectives. To evaluate, in children with Silver-Russell Syndrome, the response to the IGF-I and IGFBP-3 generation test and compare results to the growth response after 6 months of rhGH. Methods. Eight children (6 males), with a mean age of 5.71 ± 2.48 years and height SDS of -3.88 ± 1.28 received rhGH for 6 months. IGF-I and IGFBP-3 were analyzed before and after 4 doses of rhGH. Results. The mean growth velocity (GV) before treatment was 5.28 ± 1.9 cm/year. GV increased after rhGH in five children to a mean GV of 10.3 ± 3.64 cm/year. Six children had normal basal IGF-I levels and two low levels. After 4 doses of rhGH, the IGF-I levels were normal in seven. There was no correlation between the growth response and the IGF-I generation test. Conclusions. Children with SRS have normal IGF-I generation test. There is no correlation between the generation test and the growth velocity after 6 months of rhGH.

Atypical Silver-Russell phenotype resulting from maternal uniparental disomy of chromosome 7

We report on a patient with atypical Silver-Russell phenotype comprising severe growth retardation, unusual facies, bilateral Duane anomaly and infantile hypercalcemia caused by maternal uniparental iso/heterodisomy (mUPD) of chromosome 7. The development of myoclonus in this patient lends further support to the hypothesis that abnormal imprinting of the SGCE gene is responsible for some cases of myoclonus-dystonia syndrome. This case highlights the utility of SNP microarray technology as an accessible tool for the diagnosis of mUPD7 in atypical cases. We propose that depending on the balance of iso- and heterodisomic segments in a particular patient, mUPD7 may result in a range of phenotypes not confined to classic Silver-Russell syndrome.

CCMG guidelines: prenatal and postnatal diagnostic testing for uniparental disomy

The aim of this statement is to provide clinicians, cytogeneticists and molecular geneticists of the Canadian College of Medical Geneticists (CCMG) a comprehensive review of the role of UPD in constitutional genetic diagnosis and to provide a guideline as to when investigation for UPD is recommended. Members of the CCMG Cytogenetics, Molecular Genetics, Clinical Practice, and Prenatal Diagnosis committees reviewed the relevant literature on uniparental disomy (UPD) in constitutional genetic diagnosis (May 2010). Guidelines were developed for UPD testing in Canada. The guidelines were circulated for comment to the CCMG members at large and following appropriate modification, approved by the CCMG Board of Directors (July 2010).

EPIGENETIC PROGRAMMING AND FETAL GROWTH RESTRICTIONS

Normal fetal growth and development depends on multiple molecular mechanisms that coordinate both placental and fetal development. Efforts to better understand fetal/placental growth dysregulation and fetal growth restriction (FGR) are now being driven by several findings that highlight the longterm impact of FGR on susceptibility to disease. The association of poor fetal growth to perinatal medical complications is well accepted but more recent data also show that FGR is linked to common, serious adult health problems. Several large-scale human epidemiological studies from diverse countries have shown that conditions such as coronary heart disease, hypertension, stroke, type 2 diabetes mellitus, adiposity, insulin resistance and osteoporosis are more prevalent in individuals with a history of low birthweight.

Review and hypothesis: syndromes with severe intrauterine growth restriction and very short stature--are they related to the epigenetic mechanism(s) of fetal survival involved in the developmental origins of adult health and disease?

Diagnosing the specific type of severe intrauterine growth restriction (IUGR) that also has post-birth growth restriction is often difficult. Eight relatively common syndromes are discussed identifying their unique distinguishing features, overlapping features, and those features common to all eight syndromes. Many of these signs take a few years to develop and the lifetime natural history of the disorders has not yet been completely clarified. The theory behind developmental origins of adult health and disease suggests that there are mammalian epigenetic fetal survival mechanisms that downregulate fetal growth, both in order for the fetus to survive until birth and to prepare it for a restricted extra-uterine environment, and that these mechanisms have long lasting effects on the adult health of the individual. Silver-Russell syndrome phenotype has recently been recognized to be related to imprinting/methylation defects. Perhaps all eight syndromes, including those with single gene mutation origin, involve the mammalian mechanism(s) of fetal survival downsizing. Insights into those mechanisms should provide avenues to understanding the natural history, the heterogeneity and possible therapy not only for these eight syndromes, but for the common adult diseases with which IUGR is associated.

Clinically distinct epigenetic subgroups in Silver-Russell syndrome: the degree of H19 hypomethylation associates with phenotype severity and genital and skeletal anomalies

CONTEXT

The H19 imprinting control region (ICR), located on chromosome 11p15.5, has been reported hypomethylated in 20-65% of Silver-Russell syndrome (SRS) patients.

OBJECTIVE

We investigated the methylation status of 11p15.5 ICRs in SRS patients and children born small for gestational age (SGA) to clarify the relationship between phenotype and H19 methylation status.

METHODS

We performed methylation screens of the H19 and KCNQ1OT1 ICRs in 42 SRS patients, including seven maternal uniparental disomy of chromosome 7 patients, and 90 SGA children without SRS. Clinical data were evaluated from patient records, and seven hypomethylated patients were clinically and radiologically reexamined.

RESULTS

H19 ICR hypomethylation was found in 62% of SRS patients but in no SGA children. A clinical severity score demonstrated strong correlation between hypomethylation level and phenotype severity. Hypomethylation related to a more severe SRS phenotype, in which especially asymmetry and micrognathia were significantly more common. Extremely hypomethylated patients had abnormally high lumbar vertebrae, lumbar hypomobility, elbow subluxations, and distinct hand and foot anomalies. They also presented with congenital aplasia of the uterus and upper vagina, equivalent to the Mayer-Rokitansky-Küster-Hauser syndrome in females, and cryptorchidism and testicular agenesis in males.

CONCLUSIONS

We found a dose-response relationship between the degree of H19 hypomethylation and phenotype severity in SRS. We report for the first time the association of specific anomalies of the spine, elbows, hands and feet, and genital defects in SRS with severe H19 hypomethylation. Classical SRS features were found in H19 hypomethylation and milder symptoms in maternal uniparental disomy of chromosome 7, thus distinguishing two separate clinical and etiological subgroups.

Maternal uniparental disomy 7 and Silver-Russell syndrome - clinical update and comparison with other subgroups

Maternal uniparental disomy (UPD) 7 is found in approximately 5% of patients with Silver-Russell syndrome. By a descriptive and comparative clinical analysis of all published cases (more than 60 to date) their phenotype is updated and compared with the clinical findings in patients with Sliver-Russell syndrome (SRS) of either unexplained etiology or epimutations of the imprinting center region 1 (ICR1) on 11p15. The higher frequency of relative macrocephaly and high forehead/frontal bossing makes the face of patients with epimutations of the ICR1 on 11p15 more distinctive than the face of cases with SRS of unexplained etiology or maternal UPD 7. Because of the distinct micrognathia in the latter, their triangular facial gestalt is more pronounced than in the other groups. However, solely by clinical findings patients with maternal UPD 7 cannot be discriminated unambiguously from patients with epimutations of the ICR1 on 11p15 or SRS of unexplained etiology. Therefore, both loss of methylation of the ICR1 on 11p15 and maternal UPD 7 should be investigated for if SRS is suspected.

Epigenetics in Silver-Russell syndrome

Silver-Russell syndrome (SRS) is a clinically heterogeneous syndrome characterized by intra-uterine and postnatal growth retardation with spared cranial growth, dysmorphic features and frequent body asymmetry. Various cytogenetic abnormalities have been described in a small number of SRS or SRS-like cases involving chromosomes 7, 8, 11, 15, 17 and 18. However, until recent data became available involving imprinted genes on chromosome 7 and chromosome 11p15, the molecular cause of the syndrome was unknown in most cases. Genomic imprinting is the best example of transcriptional control of genes by epigenetic modifications. Many imprinted genes play key roles in fetal and placental growth and behaviour. This is illustrated in SRS, which can now be considered as a new imprinting disease model. These new findings in the pathophysiology of SRS allow long-term follow-up studies to be performed based on molecular diagnosis. This could help to define appropriate clinical guidelines regarding growth and feeding difficulties.

Prenatal testing for uniparental disomy: indications and clinical relevance

This review aims to provide a rational and ethical basis for prenatal testing for uniparental disomy (UPD) in cases with abnormal ultrasound findings or numeric and/or structural chromosomal aberrations in chorionic villous or amniotic fluid samples. The clinical phenotypes of the genomic imprinting-associated paternal UPD 6 (transient neonatal diabetes mellitus), maternal UPD 7 (Silver-Russell syndrome), paternal UPD 11p (Beckwith-Wiedemann syndrome), maternal UPD 14 (precocious puberty, short stature and highly variable developmental delay), paternal UPD 14 (polyhydramnios and a bell-shaped thorax), maternal UPD 15 (Prader-Willi syndrome), paternal UPD 15 (Angelman syndrome), maternal UPD 16 and UPD 20, as well as the diagnostic options, are summarized. In addition, the clinical impact of UPD testing and its relevance in various prenatal diagnostic situations are discussed. As a general rule, prenatal UPD testing, following genetic counseling, is justified if paternal UPD 14, maternal UPD 15 or paternal UPD 15 are suspected. In contrast, considering the mild phenotypes of paternal UPD 6 and maternal UPD 7, prenatal UPD testing is questionable. Because of the highly variable phenotype for paternal UPD 11p, maternal UPD 14 and maternal UPD 16, prenatal testing should be discussed critically on an individual basis. For all other chromosomes, prenatal UPD testing is purely academic and should therefore not be performed on a routine basis, particularly because a positive result might confuse the parents more than it actually helps them.

Maternal heterodisomy/isodisomy and paternal supernumerary ring of chromosome 7 in a child with Silver-Russell syndrome

Silver-Russell syndrome (SRS) is clinically variable although most cases have several common signs. Different chromosomes and chromosomal regions have been associated with SRS. Maternal uniparental disomy (UPD) of chromosome 7 is responsible for 5-10% of cases, probably because of an imbalance between maternal and paternal imprinted genes and more recently maternal duplication or epimutations in the 11p15 imprinted region have been described. To date, only two patients with maternal UPD7 and a mosaic condition for a supernumerary ring 7 marker have been reported, and we here report a further case. Standard QFQ banding of lymphocytes as well as fluorescence in-situ hybridization analyses were performed to identify and characterize the supernumerary marker. UPD testing was performed on both the patient's and parents' DNA using chromosome 7 microsatellite markers. The patient demonstrated a ring in about 4% of the analysed cells. On the basis of cytogenetic and molecular results, break points were tentatively identified as 7p11.2 and 7q21. Maternal hetero-/iso-UPD and a paternal origin for the supernumerary ring were demonstrated. Clinical data comparison between our patient who has a SRS phenotype and cases with hetero-/iso-UPD7 mat and mosaicism for a paternally derived chromosome 7 ring and previously reported ring 7 cases suggest that the SRS phenotype is probably because of the UPD rather than to the partial trisomy.

Growth parameters in maternal uniparental disomy 7 and 14

INTRODUCTION

Growth retardation has been reported in most cases of maternal uniparental disomy (UPD) 7 and 14, but has never been evaluated in a systematic approach. In this study, an analysis is presented of the auxological data from the literature at birth and on the occasion of the last evaluation of 34 cases with maternal UPD 7 (21 heterodisomy, 13 isodisomy) and 29 cases with maternal UPD 14 (22 heterodisomy, 7 isodisomy). For maternal UPD 7, statistical analysis revealed that length and weight at birth as well as on the occasion of the last evaluation were strongly below average (-2.94 SD and -2.62 SD, and -3.39 SD and -3.11 SD, respectively), whereas at both evaluations occipitofrontal head circumference (OFC) was only slightly below the average (-1.00 SD and -0.85 SD). For maternal UPD 14 at birth, growth retardation is rather concordant for length, weight, and OFC (-2.78 SD, -2.84 SD, and -1.69 SD). Later in life body mass index (BMI) is above average (1.06 SD) and continuously increasing before and after puberty (-0.58 SD and 2.07 SD).

CONCLUSION

Growth retardation and relative macrocephaly are of prenatal onset and still present in adults with maternal UPD 7. For patients with maternal UPD 14, growth curves for height, BMI and OFC differ strongly. Genomic imprinting might be a major causative factor, but it seems to function differently for maternal UPD 7 and maternal UPD 14.

Maternally inherited duplication of chromosome 7, dup(7)(p11.2p12), associated with mild cognitive deficit without features of Silver-Russell syndrome

We report on a familial duplication in the short arm of chromosome 7, dup(7)(p11.2p12), present in three generations. The duplication was identified by GTG-banding and fluorescence in situ hybridization (FISH) with a whole chromosome 7 DNA painting probe that verified that the duplicated material originated from chromosome 7. The multicolor banding (mBAND) was used to refine the breakpoint assignment. The duplication identified in the proband was also present in her son and mother. All three carriers have mild cognitive deficiencies. Interstitial duplications of the short arm of chromosome 7, although relatively uncommon, have been described in association with a variety of clinical features, including mental retardation of varying severity. Duplication of the p11.2p13 region on chromosome 7 was reported in association with Silver-Russell syndrome (SRS), and an overlapping dup(7)(p11.2p14.1)dn was described in an individual with autistic disorder. Furthermore, a potentially overlapping maternally transmitted inverted duplication, dup(7)(p13p12.2), was reported in patients with cognitive delay. These observations and the phenotype of our duplication carriers suggest that partial trisomy of the proximal 7p region causes cognitive deficiency. The maternal origin of the duplication is of special interest in light of genomic imprinting and implication of the 7p11-p13 region in the SRS etiology. Locus-specific FISH targeting a growth factor receptor binding protein 10 (GRB10), the strong candidate for SRS residing at 7p12.2, showed that it is not duplicated in our patients. Our study helps refine the SRS critical region on 7p and extends our understanding of the clinical manifestations associated with 7p duplications.

Imprinted genes and their role in human fetal growth

Growth is defined as the progressive increase in size and is listed as one of the eight main characteristics of life. In human gestation the most rapid growth phase is from 16 to 32 weeks when first there is both cell number and size increase and then from 32 weeks onwards there is continued size increase (Pollack and Divon, 1992). The mechanism of growth in utero is of fundamental interest to clinicians and scientists because of its implications for neonatal health. Growth is multifactorial in origin with both genetics and environment contributing equally large parts. Despite this complexity analysis of the candidate genes involved is possible using simple tissue biopsies at the relevant stages of development. Of particular interest in understanding fetal growth is the analysis of a group of genes that show a parent-of-origin effect known as genomic imprinting. Imprinted genes are not only found in eutherian (placental) and metatherian (marsupial) mammals but surprisingly also in plants. Nevertheless, their evolution in mammals appears to be linked primarily to placentation. It is thought to result from a potential conflict between the parents in terms of the drive to successfully propagate their own separate genes and the mother's added drive for her survival through the pregnancy to reproduce again. This means that the mother wants to restrict fetal growth and the father to enhance it.

Diagnostic proceeding in Silver-Russell syndrome

BACKGROUND

Silver-Russell syndrome (SRS) describes a uniform malformation syndrome characterized by pre- and postnatal growth restriction (<3rd percentile) and a typical craniofacial gestalt. The basic defect of SRS is currently unknown, and the number of meaningful genetic tests available is therefore limited. Different chromosomal aberrations have been identified, including in the chromosomal region 7p12-p14. Detailed analyses of numerous candidate genes have not revealed any relevant insights with respect to the etiology of the disease.However, maternal uniparental disomy (UPD) of chromosome 7 (matUPD7), the inheritance of both homologues of chromosome 7 only from the mother, is observed in approximately 10% of SRS patients. Here, we report on our experiences of UPD testing in patients referred to our laboratory with the clinical diagnosis of SRS. A diagnostic algorithm for SRS is suggested.

METHODS

Eighty-six patients with the clinical diagnosis of SRS were screened for matUPD7 by microsatellite typing. In 13 cases, the clinical data were consistent with the diagnosis of SRS. The other 73 patients were referred for UPD testing with the suspected diagnosis of SRS, but clinical data were scarce.

RESULTS

In total, we identified three new cases of matUPD7: one patient belonged to the cohort of 13 clinically characterized patients; the other two patients were referred with the suspected diagnosis of SRS but initially without detailed reports. DNA studies revealed uniparental heterodisomy 7 in two patients, while the results in the third case were consistent with uniparental isodisomy.

CONCLUSIONS

MatUPD7 is predominantly detectable in patients showing SRS features, and testing should therefore be restricted to this group of growth-restricted patients. Generally, a combination of cytogenetic and molecular genetic tests can be offered in SRS, aiming at the detection of chromosomal rearrangements and matUPD7 in >10% of SRS patients.

Paternal isodisomy of chromosome 7 with cystic fibrosis and overgrowth

We have diagnosed a boy with cystic fibrosis (CF) due to paternal UPD presenting with overweight and developmental delay, not typical features to CF patients. Two previously reported patients with paternal UPD(7) did not present overgrowth. The discrepancy between the phenotype of this boy and the other two patients raises the question of imprinted genes or homozygotization of a disease-causing gene in paternal UPD7.

Trisomy 7 mosaicism, maternal uniparental heterodisomy 7 and Hirschsprung's disease in a child with Silver–Russell syndrome

Prenatal trisomy 7 is usually a cell culture artifact in amniocytes with normal diploid karyotype at birth and normal fetal outcome. In the same way, true prenatal trisomy 7 mosaicism usually results in a normal child except when trisomic cells persist after birth or when trisomy rescue leads to maternal uniparental disomy, which is responsible for 5.5-7% of patients with Silver-Russell syndrome (SRS). We report here on the unusual association of SRS and Hirschsprung's disease (HSCR) in a patient with maternal uniparental heterodisomy 7 and trisomy 7 mosaicism in intestine and skin fibroblasts. HSCR may be fortuitous given its frequency, multifactorial inheritance and genetic heterogeneity. However, the presence of the trisomy 7 mosaicism in intestine as well as in skin fibroblasts suggests that SRS and HSCR might possibly be related. Such an association might result from either an increased dosage of a nonimprinted gene due to trisomy 7 mosaicism in skin fibroblasts (leading to SRS) and in intestine (leading to HSCR), or from an overexpression, through genomic imprinting, of maternally expressed imprinted allele(s) in skin fibroblasts and intestine or from a combination of trisomy 7 mosaicism and genomic imprinting. This report suggests that the SRS phenotype observed in maternal uniparental disomy 7 (mUPD(7)) patients might also result from an undetected low level of trisomy 7 mosaicism. In order to validate this hypothesis, we propose to perform a conventional and molecular cytogenetic analysis in different tissues every time mUPD7 is displayed.

Global analysis of uniparental disomy using high density genotyping arrays

BACKGROUND

Uniparental disomy (UPD), the inheritance of both copies of a chromosome from a single parent, has been identified as the cause for congenital disorders such as Silver-Russell, Prader-Willi, and Angelman syndromes. Detection of UPD has largely been performed through labour intensive screening of DNA from patients and their parents, using microsatellite markers.

METHODS

We applied high density single nucleotide polymorphism (SNP) microarrays to diagnose whole chromosome and segmental UPD and to study the occurrence of continuous or interspersed heterodisomic and isodisomic regions in six patients with Silver-Russell syndrome patients who had maternal UPD for chromosome 7 (matUPD7).

RESULTS

We have devised a new high precision and high-throughput computational method to confirm UPD and to localise segments where transitions of UPD status occur. Our method reliably confirmed and mapped the matUPD7 regions in all patients in our study.

CONCLUSION

Our results suggest that high density SNP arrays can be reliably used for rapid and efficient diagnosis of both segmental and whole chromosome UPD across the entire genome.

Paternal uniparental disomy of chromosome 14 and unique exchange of chromosome 7 in cases of spontaneous abortion

To investigate the involvement of uniparental disomies (UPDs) in spontaneous abortion, the polymorphic patterns of microsatellites on each chromosome were analyzed in 164 cases of abortion. Eighty-three of the 164 cases had chromosomal abnormalities. In 79 of the remaining 81 cases with normal karyotypes, the microsatellite analysis revealed that biparental patterns were present in the informative microsatellites in all chromosomes. In one of the remaining two cases, however, the polymorphic patterns of chromosome 14 appeared to be both of paternal origin. The patterns of the distal of the long arm were homozygous, and those of the remaining region were heterozygous. That is, this fetus had paternal UPD 14, originating from meiosis I nondisjunction. In the other case, the polymorphic patterns of the distal one third of the long arm of chromosome 7 were uniparental (maternal) in origin whereas those of the remaining region of this chromosome were biparental. These findings thus suggested that this chromosome might have originated from chromatid exchange between the long arms of paternal and maternal chromosome 7 at the first mitotic division. Microsatellite analysis, however, produced no evidence of duplication or deletion of any segments. The findings also suggest the possibility that some UPDs may cause spontaneous abortion.

An interstitial deletion of chromosome 7 at band q21: A case report and review

We report on a girl with moderate developmental delay and mild dysmorphic features. Cytogenetic investigations revealed a de novo interstitial deletion at the proximal dark band on the long arm of chromosome 7 (7q21.1-q21.3) in all analyzed G-banded metaphases of lymphocytes and fibroblasts. Fluorescence in situ hybridization (FISH) and molecular studies defined the breakpoints at 7q21.11 and 7q21.3 on the paternal chromosome 7, with the proximal deletion breakpoint between the elastin gene (localized at 7q11.23) and D7S2517, and the distal breakpoint between D7S652 and the COL1A2 gene (localized at 7q21.3-q22.1). Deletions of interstitial segments at the proximal long arm of chromosome 7 at q21 are relatively rare. The karyotype-phenotype correlation of these patients is reviewed and discussed. The clinical findings of patients with a deletion at 7q21 significantly overlap with those of patients with maternal uniparental disomy of chromosome 7 (matUPD(7)) and Silver-Russell syndrome (SRS, OMIM 180860). Therefore, 7q21 might be considered a candidate chromosomal region for matUPD(7) and SRS.

Sex-specific chromosome instability in early human development

The predominance of females segregating chromosome aberrations to their offspring has been explained mostly by selection disadvantage of unbalanced products of spermatogenesis. However, analysis of data from the literature supports the idea that somatic cells of early female embryos are similar to female germ cells in that they are prone to malsegregation. The goal of this study was to compare the sex ratio (male to female ratio) of carriers of presumably mitotic-occurring chromosome abnormalities to identify any sex biases. In examining the literature, we found a female prevalence in cases of mosaicism associated with uniparental disomy (UPD) (26 male individuals/conceptions and 45 female individuals/conceptions, sex ratio is 0.58, significantly different from 1.06 in newborn population, P = 0.0292). This predominance was highest at gestational age <16 week (8 male and 22 female conceptuses, sex ratio is 0.36, significantly different from expected figure of 1.28, P = 0.0025), which diminished at later stages of fetal development indicating potential correction of trisomies predominantly in females. There is a threefold prevalence of 46,XX/45,X mosaics over 46,XY/45,X mosaics in prenatally diagnosed cases, which also suggests a gender-specific postzygotic chromosome loss. The male prevalence in Prader-Willi syndrome with maternal UPD of chromosome 15 also can be explained by sex-specific trisomy correction, with predominant loss of a maternal chromosome causing biparental inheritance and therefore, complete correction of trisomy in females (without UPD). Finally, there is a female predominance in carriers of chromosome rearrangement with pericentromere break (mosaicism for Robertsonian translocation/isochromosome, centric fission, nonacrocentric isochromosome, and whole arm rearrangement), in both prenatal (21 males and 36 females, sex ratio is 0.58, P < 0.0184) and postnatal ill-defined cases (14 males and 35 females, sex ratio is 0.40, P = 0.001). Thus, the findings presented in this paper suggest that, in addition to reduction in male fertility, and to probable selection against abnormal cell line(s), there are two mechanisms that contribute to female preponderance among carriers of mosaicism: sex-specific chromosome loss and sex-specific centromere instability. The data obtained suggest that females may have gonadal mosaicism for aneuploidies and structural rearrangements more often than males. This may lead to the maternal origin bias in offspring with trisomies or structural rearrangements.

Uniparental disomy (UPD) other than 15: Phenotypes and bibliography updated

Uniparental disomy (UPD) describes the inheritance of a pair of chromosomes from only one parent. The concept was introduced in Medical Genetics by Engel (1980); Am J Med Genet 6:137-143. Aside UPD 15, which is the most frequent one, up to now (February 2005) 197 cases with whole chromosome maternal UPD other than 15 (124 X heterodisomy, 59 X isodisomy, and 14 cases without information of the mode of UPD) and 68 cases with whole chromosome paternal UPD other than 15 (13 X heterdisomy, 53 X isodisomy, and 2 cases without information of the mode of UPD) have been reported. In this review we discuss briefly the problems associated with UPD and provide a comprehensive clinical summary with a bibliography for each UPD other than 15 as a guide for genetic counseling.

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.

Paternal reciprocal translocation t(11;16)(p13;q24.3) in a Silver-Russel syndrome patient

We describe a 7-month-old male child with Silver-Russel syndrome (SRS) phenotype, presented with two major clinical features: low birth weight, short stature, and minor features, such as macrocephaly, clinodactyly, essential for the diagnosis of SRS. Routine cytogenetic studies with GTG-banding showed 46,XY,t(11;16)(p13;q24.3). Fluorescence in situ hybridisation (FISH) with single copy probes BAC (11p13) and PAC (16q24.3), showed a reciprocal translocation. Chromosomal analysis of the mother was normal and the phenotypically normal father had apparently identical translocation t(11;16)(p13;q24.3). The disruption of growth factor genes at 11p and 16q breakpoint regions due to reciprocal translocation in the father might have caused SRS phenotype in the child.

A multiplex methylation PCR assay for identification of uniparental disomy of chromosome 7

Uniparental disomy of chromosome 7 (UPD7) is associated with abnormal phenotypic effects because of inappropriate expression of imprinted genes on chromosome 7. Based on the differential methylation of the promoter region of the imprinted PEG1/MEST locus at 7q32, we designed a multiplex methylation PCR (mPCR) assay to rapidly distinguish UPD7 from biparental inheritance of chromosome 7. Primers were designed to produce different sized PCR amplicons based on the parent of origin-specific methylation at this locus; electrophoresis of PCR amplicons showed a 189-bp product from the methylated maternal allele and a 109-bp product from the unmethylated paternal allele. This mPCR assay correctly predicted the chromosome 7 imprinting status in normal control and UPD7 samples. Previous assays for UPD7 required genotyping of the proband and parents, or separate maternal- and paternal-specific mPCR reactions. The advantage of this assay is that parental samples are not required and that amplification of both alleles in the same reaction is simpler and provides an internal control. This multiplex mPCR assay will be useful in screening for UPD7 in patients with Silver-Russell syndrome (SRS; also Russell-Sliver syndrome, RSS), primordial growth retardation, and in patients with supernumerary marker chromosomes or chromosome rearrangements of chromosome 7 origin.

The imprinted region on human chromosome 7q32 extends to the carboxypeptidase A gene cluster: an imprinted candidate for Silver-Russell syndrome

Imprinted gene(s) on human chromosome 7q32-qter have been postulated to be involved in intrauterine growth restriction associated with Silver-Russell syndrome (SRS) as 7-10% of patients have mUPD(7). Three imprinted genes, MEST, MESTIT1, and COPG2IT1 on chromosome 7q32, are unlikely to cause SRS since epigenetic and sequence mutation analyses have not shown any changes. One hundred kilobases proximal to MEST lies a group of four carboxypeptidase A (CPA) genes. Since most imprinted genes are found in clusters, this study focuses on analysing these CPAs for imprinting effects based on their proximity to an established imprinted domain. Firstly, a replication timing study across 7q32 showed that an extensive genomic region including the CPAs, MEST, MESTIT1, and COPG2IT1 replicates asynchronously. Subsequently, SNP analysis by sequencing RT-PCR products of CPA1, CPA2, CPA4, and CPA5 indicated preferential expression of CPA4. Pyrosequencing was used as a quantitative approach, which confirmed predominantly preferential expression of the maternal allele and biallelic expression in brain. CPA5 expression levels were too low to allow reliable evaluation of allelic expression, while CPA1 and CPA2 both showed biallelic expression. CPA4 was the only gene from this family in which an imprinting effect was shown despite the location of this family of genes next to an imprinted cluster. As CPA4 has a potential role in cell proliferation and differentiation, two preferentially expressed copies in mUPD patients with SRS syndrome would result in excess expression and could alter the growth profiles of these subjects and give rise to intrauterine growth restriction.

Prenatal diagnosis of a trisomy 7/maternal uniparental heterodisomy 7 mosaic fetus

Chromosomal segregation anomalies often result in trisomy of a single chromosome, which can lead to a disastrous phenotype in the fetus. However, this trisomy is often "rescued" via loss of one of the triploid chromosomes. Depending on which chromosome is eliminated in the rescue, a condition known as uniparental disomy may arise where both copies of a particular chromosome pair originate from the same parent. Here we describe the case of a 32-year-old woman who was prenatally diagnosed with trisomy 7 mosaicism via amniocentesis. Forty-one percent of the colonies analyzed displayed trisomy 7 (two maternal chromosomes and one paternal chromosome); whereas, 59% of the colonies demonstrated a normal, disomic karyotype. Further analysis revealed that the "normal" cell lineage displayed maternal uniparental heterodisomy. Chorionic villus tissue was homogeneously trisomic, and cord blood cells were uniformly disomic. This is the first case of trisomy 7/uniparental disomy 7 mosaic fetus reported in the literature. It is important to note that not all such cases will result in lethality or a fetus with major anatomic, developmental, or cognitive abnormalities. In addition, the benefit of pre- and post-screening test counseling and support is discussed in reference to fetuses with chromosomal abnormalities in general and our case in particular.

Genetic screening for maternal uniparental disomy of chromosome 7 in prenatal and postnatal growth retardation of unknown cause

OBJECTIVE

Many short-statured children lack an etiologic explanation for their retarded growth. Recently, uniparental disomy (UPD), the inheritance of both chromosomes of a chromosome pair from only 1 parent, has been associated with short stature for many chromosomes. Silver-Russell syndrome (SRS) represents an extreme syndrome of intrauterine growth retardation (IUGR) and slight dysmorphic signs, and maternal UPD of human chromosome 7 (matUPD7) has been observed in approximately 10% of SRS cases. In addition, matUPD7 has been reported in patients with only slight dysmorphic features and prenatal or postnatal growth retardation. The objectives of this study were to study the role of matUPD7 in growth failure of unknown cause and in cases of SRS, and to evaluate the efficiency of genetic testing for matUPD7 as a diagnostic tool.

METHODS

DNA samples were studied from 205 children, 92 girls and 113 boys, with short stature of unknown cause and their parents. The patient cohort included 39 cases of SRS, 91 patients with IUGR and subsequent postnatal short stature, and 75 patients with postnatal growth retardation only. MatUPD7 was screened for by genotyping DNA samples from the patient, mother, and father with 13 chromosome-7-specific polymorphic microsatellite markers.

RESULTS

Six (3%) of 205 matUPD7 cases were observed exclusively among 39 (15%) SRS patients studied. Patients with IUGR and/or postnatal growth retardation and with dysmorphic features did not reveal cases of matUPD7.

CONCLUSIONS

Our results indicate that matUPD7 cases are predominantly observed among patients meeting the criteria of SRS, and matUPD7 is not a common cause for growth retardation. Genetic screening for cases of matUPD7 among growth-retarded patients should be focused on patients with severe IUGR and features of SRS. In addition, matUPD7 screening is advisable in individuals with cystic fibrosis and other recessive disorders mapped to chromosome 7 who have unusually short stature.

Evidence from skewed X inactivation for trisomy mosaicism in Silver-Russell syndrome

The finding of maternal uniparental disomy for chromosome 7 (matUPD7) in approximately 7% of Silver-Russell syndrome (SRS) cases has lead to the assumption that imprinted gene(s) on chromosome 7 are responsible for at least some cases. However, the observation in a familial case that both maternal and paternal inheritance of proximal 7p results in an SRS-like phenotype suggests that the causative genes may not be imprinted, and that an extra copy of genes within this region cause SRS. As all cases of complete matUPD7 could have arisen by trisomy rescue, it is possible that undetected trisomy 7 mosaicism contributes towards the phenotype of SRS, and that the matUPD7 seen in some cases is a consequence of trisomy rescue. Previous studies in cases of trisomy rescue for a number of autosomes have shown a strong association with skewed X inactivation in diploid tissues. Thus, we hypothesised that if trisomy mosaicism was involved in SRS, the frequency of skewed X inactivation should be increased in a population of non-matUPD7 SRS patients. Consistent with this hypothesis, results showed a significant increase in the frequency of completely skewed X inactivation in SRS patients (three of 29) when compared to controls (three of 270), suggesting the possible presence of undetected trisomy 7 in SRS patients and/or their placentas.

Silver-Russell syndrome: a dissection of the genetic aetiology and candidate chromosomal regions

The main features of Silver-Russell syndrome (SRS) are pre- and postnatal growth restriction and a characteristic small, triangular face. SRS is also accompanied by other dysmorphic features including fifth finger clinodactyly and skeletal asymmetry. The disorder is clinically and genetically heterogeneous, and various modes of inheritance and abnormalities involving chromosomes 7, 8, 15, 17, and 18 have been associated with SRS and SRS-like cases. However, only chromosomes 7 and 17 have been consistently implicated in patients with a strict clinical diagnosis of SRS. Two cases of balanced translocations with breakpoints in 17q23.3-q25 and two cases with a hemizygous deletion of the chorionic somatomammatropin gene (CSH1) on 17q24.1 have been associated with SRS, strongly implicating this region. Maternal uniparental disomy for chromosome 7 (mUPD(7)) occurs in up to 10% of SRS patients, with disruption of genomic imprinting underlying the disease status in these cases. Recently, two SRS patients with a maternal duplication of 7p11.2-p13, and a single proband with segmental mUPD for the region 7q31-qter, were described. These key patients define two separate candidate regions for SRS on both the p and q arms of chromosome 7. Both the 7p11.2-p13 and 7q31-qter regions are subject to genomic imprinting and the homologous regions in the mouse are associated with imprinted growth phenotypes. This review provides an overview of the genetics of SRS, and focuses on the newly defined candidate regions on chromosome 7. The analyses of imprinted candidate genes within 7p11.2-p13 and 7q31-qter, and gene candidates on distal 17q, are discussed.

Post-zygotic origin of complete maternal chromosome 7 isodisomy and consequent loss of placental PEG1/MEST expression

Maternal UPD of chromosome 7 is associated with pre- and postnatal growth retardation (IUGR, PNGR) and Silver-Russell syndrome (SRS [MIM 180860]). We report a case of IUGR in a newborn with SRS stigmata. Using combined haplotyping and cytogenetic-FISH studies we characterized the lymphocytes, umbilical cord and four placental cotyledons. The results are consistent with complete maternal isodisomy 7 and trisomy 7 mosaicism of post-zygotic origin. The trisomic cell line was prevalent in trophoblast cells from two placental cotyledons. Trisomy 7 of post-zygotic origin is a frequent finding, but maternal isodisomy 7, due to trisomic rescue has never been reported. PEG1/MEST expression was evaluated on placenta cDNA and a specific transcript was revealed only in the cotyledons with a high percentage of trisomic cells and the presence of the paternal chromosome 7 contribution, but not in the placental biopsies with maternal isodisomy 7. The histological features of the four placental fragments revealed that isodisomy 7 correlates with a pattern of cotyledonary hyper-ramification due to an increase of the branching angiogenesis, which could be the result of a defect of angiogenesis caused by the absence of PEG1 product. The severe hypo-ramification of the two cotyledons, showing trisomy 7 mosaicism, may be due to the triplicate dosage of genes on chromosome 7. The delayed fetal growth could be the phenotypic effect of the imbalance between imprinted and non-imprinted genes on chromosome 7 in the fetus or the result of abnormal placental function during pregnancy.

Complex and segmental uniparental disomy (UPD): review and lessons from rare chromosomal complements

OBJECTIVE

To review all cases with segmental and/or complex uniparental disomy (UPD), to study aetiology and mechanisms of formation, and to draw conclusions.

DESIGN

Searching published reports in Medline.

RESULTS

The survey found at least nine cases with segmental UPD and a normal karyotype, 22 cases with UPD of a whole chromosome and a simple or a non-homologous Robertsonian translocation, eight cases with UPD and two isochromosomes, one of the short arm and one of the long arm of a non-acrocentric chromosome, 39 cases with UPD and an isochromosome of the long arm of two homologous acrocentric chromosomes, one case of UPD and an isochromosome 8 associated with a homozygous del(8)(p23.3pter), and 21 cases with UPD of a whole or parts of a chromosome associated with a complex karyotype. Segmental UPD is formed by somatic recombination (isodisomy) or by trisomy rescue. In the latter mechanism, a meiosis I error is associated with meiotic recombination and an additional somatic exchange between two non-uniparental chromatids. Subsequently, the chromatid that originated from the disomic gamete is lost (iso- and heterodisomy). In cases of UPD associated with one isochromosome of the short arm and one isochromosome of the long arm of a non-acrocentric chromosome and in cases of UPD associated with a true isochromosome of an acrocentric chromosome, mitotic complementation is assumed. This term describes the formation by misdivision at the centromere during an early mitosis of a monosomic zygote. In cases of UPD associated with an additional marker chromosome, either mitotic formation of the marker chromosome in a trisomic zygote or fertilisation of a gamete with a marker chromosome formed in meiosis by a disomic gamete or by a normal gamete and subsequent duplication are possible.

CONCLUSIONS

Research in the field of segmental and/or complex UPD may help to explain undiagnosed non-Mendelian disorders, to recognise hotspots for meiotic and mitotic recombinations, and to show that chromosomal segregation is more complex than previously thought. It may also be helpful to map autosomal recessively inherited genes, genes/regions of genomic imprinting, and dysmorphic phenotypes. Last but not least it would improve genetic counselling.

Maternal isochromosome 7q and paternal isochromosome 7p in a boy with growth retardation

A 12-year 9-month-old boy with postnatal growth retardation, normal psychomotor development, and minor anomalies that included a triangular-shaped face, small nose, and narrow and high-arched palate is reported. The constitutional karyotype was 46,XY,i(7)(p10),i(7)(q10). Molecular investigations revealed the presence of a maternal isodisomy 7q and a paternal isodisomy 7p. The clinical and molecular findings are notably congruent with a recently reported case and support the hypothesis of one or more maternally imprinted genes located on the long arm of chromosomes 7 that regulate, in particular, postnatal growth.

Cytogenetic analyses of culture failures by comparative genomic hybridisation (CGH)-Re-evaluation of chromosome aberration rates in early spontaneous abortions

Comparative genomic hybridisation (CGH) represents an alternative molecular-cytogenetic technique capable of detecting chromosomal imbalances by reverse fluorescence in situ hybridisation. As the technique uses genomic DNA for assessment it does not rely on metaphase chromosomes in the test material and thus circumvents technical problems associated with tissue culturing. In the present study, we applied CGH to identify chromosome anomalies in 60 spontaneous abortions of the first trimester, that had failed to grow in culture. In 57 out of 60 cases CGH analyses were successful. The overall aneuploidy rate detected was 72%. Trisomy was the predominant chromosome anomaly accounting for 68.0% of abnormal abortions, followed by triploidy (17.1%) and monosomy X (9.8%). An unbalanced structural rearrangement was found in one (2.4%) abortion. Most frequently involved in trisomies were chromosomes 16 (32.1%), 7 and 22 (10.7% each), 4, 13, 15, and 21 (7.2 % each). Three triploid cases and one complete mole were detected by microsatellite analysis as supplementary method. CGH data on culture failures were compared with data derived from 4693 successfully karyotyped first trimester spontaneous abortions, resulting in a chromosome aberration rate of 64.8%. The distribution of the different chromosome anomalies was similar with the exception of a higher rate of trisomies 7 and of XYY-triploidies in the culture failures. Based on our data we suggest that the genetic contribution to pregnancy loss is still underestimated. Investigating abortion tissues hitherto unassessed by conventional methods, we suggest that the contribution of chromosome aberrations to first trimester pregnancy loss is nearly 70%.