The genetics of the Silver-Russell syndrome

Effect of uniparental disomy in parentage testing

Uniparental disomy (UPD) is a rare type of chromosomal aberration that may hinder the analysis of kinship during forensic identification. Here, we investigated these genetic findings to avoid false exclusions during parentage testing. Thirty-nine fluorescently labeled, autosomal short tandem repeats (STR) were amplified in three cases, to detect parent-child relationships. Twenty-three fluorescently labeled Y-chromosome STRs were also employed. These were subjected to capillary electrophoresis. The parentage index was calculated by the bipartite or tripartite model. Single nucleotide polymorphism (SNP) microarrays were performed to further investigate the genetic mechanisms. The conclusions supported the biological mother-child relationship in three cases. However, in all cases, the alleged father and child had three autosomal STR markers, constrained to a single chromosome, which did not conform to Mendelian inheritance rules. The genotyping of 23 Y-chromosome STRs did not reveal any violations of Mendelian law. The combination of STR profiling and SNP microarrays suggested that two children had maternal UPD of chromosome 7, whilst one had UPD of chromosome 2. After excluding the three incompatible loci, the conclusions supported the biological father-child relationship in all cases. The same results were obtained when parentage testing of trios was used. Uniparental disomy may complicate the judgment of kinship in parentage testing. The possibility of UPD should be considered when incompatible STR loci are found on the same chromosome. Genetic evidence obtained through additional molecular techniques can provide better interpretation of kinship in the presence of UPD and avoid false exclusions of biological relationships.

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%).

Complex tissue-specific epigenotypes in Russell-Silver Syndrome associated with 11p15 ICR1 hypomethylation

Russell-Silver Syndrome (RSS) is a prenatal and postnatal growth retardation syndrome caused mainly by 11p15 ICR1 hypomethylation. Clinical presentation is heterogeneous in RSS patients with 11p15 ICR1 hypomethylation. We previously identified a subset of RSS patients with 11p15 ICR1 and multilocus hypomethylation. Here, we examine the relationships between IGF2 expression, 11p15 ICR1 methylation, and multilocus imprinting defects in various cell types from 39 RSS patients with 11p15 ICR1 hypomethylation in leukocyte DNA. 11p15 ICR1 hypomethylation was more pronounced in leukocytes than in buccal mucosa cells. Skin fibroblast IGF2 expression was correlated with the degree of ICR1 hypomethylation. Different tissue-specific multilocus methylation defects coexisted in 38% of cases, with some loci hypomethylated and others hypermethylated within the same cell type in some cases. Our new results suggest that tissue-specific epigenotypes may lead to clinical heterogeneity in RSS.

Intrauterine and postnatal growth failure with normal GH/IGF1 axis and insulin-resistant diabetes in a consanguineous kinship

OBJECTIVE

To describe the clinical and biochemical features, and perform molecular analysis for candidate abnormalities in a novel familial syndrome of intrauterine growth retardation (IUGR), failure of an adolescent growth spurt with proportional adult short stature, minimal subluxation of the 5th metacarpal-phalangeal joint, and adult-onset insulin-resistant diabetes unrelated to obesity or other manifestations of metabolic syndrome (MS).

DESIGN

Detailed clinical history, auxological, biochemical, radiological, and molecular studies, including DNA analysis and in vitro study of the GH/IGF1 pathway.

MATERIALS AND METHODS

Ten affected adults from two generations of five related families were studied in detail, and information obtained about nine other likely affected individuals.

RESULTS

Height Z-scores ranged from -7.3 to -3.8. Unaffected parents of the older generation and frequency of confirmed and suspected instances of the syndrome in the two generations studied is consistent with autosomal recessive inheritance. Insulin resistance was uniformly present in seven subjects tested who were not taking insulin. Diabetes severity did not correlate with overweight. Subjects did not have other typical manifestations of MS such as substantial hyperlipidemia, osteoporosis, or hypertension. No biochemical abnormality in the GH/IGF1 axis or molecular defect was found.

CONCLUSIONS

While the association of IUGR and adult MS, including diabetes, has been well documented, these subjects did not have typical manifestations of MS. Abnormalities in common components that could result in a combination of IUGR, severe postnatal growth, and insulin resistance have been ruled out. A mutation in an unidentified gene may affect intrauterine and postnatal growth, with insulin resistance directly affected or as a result of this growth phenomenon.

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.

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.

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.

11p15 imprinting center region 1 loss of methylation is a common and specific cause of typical Russell-Silver syndrome: clinical scoring system and epigenetic-phenotypic correlations

CONTEXT

Russell-Silver syndrome (RSS), characterized by intrauterine and postnatal growth retardation, dysmorphic features, and frequent body asymmetry, spares cranial growth. Maternal uniparental disomy for chromosome 7 (mUPD7) is found in 5-10% of cases. We identified loss of methylation (LOM) of 11p15 Imprinting Center Region 1 (ICR1) domain (including IGF-II) as a mechanism leading to RSS.

OBJECTIVE

The aim was to screen for 11p15 epimutation and mUPD7 in RSS and non-RSS small-for-gestational-age (SGA) patients and identify epigenetic-phenotypic correlations. STUDIED POPULATION AND METHODS: A total of 127 SGA patients were analyzed. Clinical diagnosis of RSS was established when the criterion of being SGA was associated with at least three of five criteria: postnatal growth retardation, relative macrocephaly, prominent forehead, body asymmetry, and feeding difficulties. Serum IGF-II was evaluated for 82 patients.

RESULTS

Of the 127 SGA patients, 58 were diagnosed with RSS; 37 of these (63.8%) displayed partial LOM of the 11p15 ICR1 domain, and three (5.2%) had mUPD7. No molecular abnormalities were found in the non-RSS SGA group (n = 69). Birth weight, birth length, and postnatal body mass index (BMI) were lower in the abnormal 11p15 RSS group (ab-ICR1-RSS) than in the normal 11p15 RSS group [-3.4 vs.-2.6 SD score (SDS), -4.4 vs.-3.4 SDS, and -2.5 vs.-1.6 SDS, respectively; P < 0.05]. Among RSS patients, prominent forehead, relative macrocephaly, body asymmetry, and low BMI were significantly associated with ICR1 LOM. All ab-ICR1-RSS patients had at least four of five criteria of the scoring system. Postnatal IGF-II levels were within normal values.

CONCLUSION

The 11p15 ICR1 epimutation is a major, specific cause of RSS exhibiting failure to thrive. We propose a clinical scoring system (including a BMI < -2 SDS), highly predictive of 11p15 ICR1 LOM, for the diagnosis of RSS.

Intracytoplasmic sperm injection--an assisted reproduction technique that should make us cautious about imprinting deregulation

OBJECTIVE

Due to the extensive use of intracytoplasmic sperm injection (ICSI) in assisted reproduction, not only among couples with severe male factor infertility problems, but to a broader scale, a lot of concern has been raised regarding the safety of the method and its implications in epigenetic control and imprinting dysregulation. This review means to provide a comprehensive report of the published scientific data, outline putative associations between ICSI and epigenetic control, and suggest measures to improve the current state of affairs and reach more scientifically consolidated results.

METHODS

This review was conducted by studying a broad spectrum of articles dealing with the subject of epigenetic control and its relation with ICSI. We tried to view the two subjects as parallel procedures that occur in the organism and by delineating the molecular and biochemical steps that comprise them make suggestions about putative associations between ICSI and epigenetic control.

CONCLUSIONS

No hard evidence presented at the moment can prove or disapprove ICSI's implications in epigenetic control. Nevertheless, we take the view that more comprehensive, long-term, and properly designed studies are imperative to be applied on a large-scale basis. We urge cautiousness, since the welfare of our progeny is what is at stake.

Regulation of growth and metabolism by imprinted genes

A small sub-set of mammalian genes are subject to regulation by genomic imprinting such that only one parental allele is active in at least some sites of expression. Imprinted genes have diverse functions, notably including the regulation of growth. Much attention has been devoted to the insulin-like growth factor signalling pathway that has a major influence on fetal size and contains two components encoded by the oppositely imprinted genes, Igf2 (a growth promoting factor expressed from the paternal allele) and Igf2r (a growth inhibitory factor expressed from the maternal allele). These genes fit the parent-offspring conflict hypothesis for the evolution of genomic imprinting. Accumulated evidence indicates that at least one other fetal growth pathway exists that has also fallen under the influence of imprinting. It is clear that not all components of growth regulatory pathways are encoded by imprinted genes and instead it may be that within a pathway the influence of a single gene by each of the parental genomes may be sufficient for parent-offspring conflict to be enacted. A number of imprinted genes have been found to influence energy homeostasis and some, including Igf2 and Grb10, may coordinate growth with glucose-regulated metabolism. Since perturbation of fetal growth can be correlated with metabolic disorders in adulthood these imprinted genes are considered as candidates for involvement in this phenomenon of fetal programming.

Gametes and embryo epigenetic reprogramming affect developmental outcome: implication for assisted reproductive technologies

There is concern about the health of children who are conceived with the use assisted reproductive technologies (ART). In addition to reports of low birth weight and chromosomal anomalies, there is evidence that ART may be associated with increased epigenetic disorders in the infants who are conceived using these procedures. Epigenetic reprogramming is critical during gametogenesis and at preimplantation stage and involves DNA methylation, imprinting, RNA silencing, covalent modifications of histones, and remodeling by other chromatin-associated complexes. Epigenetic regulation is involved in early embryo development, fetal growth, and birth weight. Disturbances in epigenetic reprogramming may lead to developmental problems and early mortality. Recent reports suggest the increased incidence of imprinting disorders such as Beckwith-Wiedemann syndrome, Angelman syndrome, and retinoblastoma in children who are conceived with the use of ART. These may result from an accumulation of epigenetic alterations during embryo culture and/or by altered embryonic developmental timing. Further research is urgently needed to determine whether a causal relationship between ART and epigenetic disorders exists. Until then, cautious review of both short-term and long-term ART outcomes at a national level is recommended.

Epigenetics and the germline

Epigenetic processes affect three stages of germline development, namely (1) specification and formation of primordial germ cells and their germline derivatives through lineage-specific epigenetic modifications, in the same manner as other embryonic lineages are formed, (2) a largely genome-wide erasure and re-establishment of germline-specific epigenetic modifications that only occurs in the embryonic primordial germ cell lineage, followed by re-establishment of sex-specific patterns during gametogenesis, and (3) differential epigenetic modifications to the mature male and female gamete genomes shortly after fertilisation. This review will detail current knowledge of these three processes both at the genome-wide level and at specific imprinted loci. The consequences of epigenetic perturbation are discussed and new in vitro models which may allow further understanding of a difficult developmental period to study, especially in the human, are highlighted.