Genetics of Silver-Russell syndrome

Russell-Silver Syndrome With Growth Hormone Deficiency

Russell-Silver syndrome (RSS) is a rare genetic disorder characterized by intrauterine growth restriction (IUGR), postnatal growth failure, and distinctive dysmorphic features. We present a case of a four-year-old male presenting with a slow growth velocity with a history of IUGR and surgical interventions, exhibiting classic RSS features. Laboratory investigations revealed low insulin-like growth factor 1 (IGF-1) and low growth hormone (GH) levels on stimulation tests. Clinical exome sequencing revealed a de novo mutation in the insulin-like growth factor 2 (IGF2) gene. Additionally, a variant of uncertain significance in the DHX37 gene was noted in the patient and the asymptomatic father. After genetic counseling, recombinant GH therapy was initiated. This case underscores the genetic complexity of RSS and highlights the importance of early diagnosis, genetic testing, and multidisciplinary management in optimizing outcomes for patients with RSS.

Nonparametric method for detecting imprinting effect using all members of general pedigrees with missing data

Imprinting effects can lead to parent-of-origin patterns in complex human diseases. For a diallelic marker locus, Pedigree Parental-Asymmetry Test (PPAT) and its extension MCPPAT using pedigrees allowing for missing genotypes are simple and powerful for detecting imprinting effects. However, these approaches only take affected offspring into consideration, thus not making full use of the data available. In this paper, we propose Monte Carlo Pedigree Parental-Asymmetry Test using both affected and unaffected (MCPPATu) offsprings, which allows for missing genotypes through Monte Carlo sampling. Simulation studies demonstrate that MCPPATu controls the empirical type I error rate well under the null hypotheses of no parent-of-origin effects. It is also demonstrated that the use of additional information from unaffected offspring and partially observed genotypes in the analysis can greatly improve the statistical power. Indeed, for common diseases, MCPPATu is much more powerful than MCPPAT when all genotypes are observed and the power improvement is even greater when there is missing data. For rarer diseases, there are still substantial power gains with the inclusion of unaffected offspring, although the gains are less impressive compared with those for more common diseases.

Peromyscus (deer mice) as developmental models

Deer mice (Peromyscus) are the most common native North American mammals, and exhibit great natural genetic variation. Wild-derived stocks from a number of populations are available from the Peromyscus Genetic Stock Center (PGSC). The PGSC also houses a number of natural variants and mutants (many of which appear to differ from Mus). These include metabolic, coat-color/pattern, neurological, and other morphological variants/mutants. Nearly all these mutants are on a common genetic background, the Peromyscus maniculatus BW stock. Peromyscus are also superior behavior models in areas such as repetitive behavior and pair-bonding effects, as multiple species are monogamous. While Peromyscus development generally resembles that of Mus and Rattus, prenatal stages have not been as thoroughly studied, and there appear to be intriguing differences (e.g., longer time spent at the two-cell stage). Development is greatly perturbed in crosses between P. maniculatus (BW) and Peromyscus polionotus (PO). BW females crossed to PO males produce growth-restricted, but otherwise healthy, fertile offspring which allows for genetic analyses of the many traits that differ between these two species. PO females crossed to BW males produce overgrown but severely dysmorphic conceptuses that rarely survive to late gestation. There are likely many more uses for these animals as developmental models than we have described here. Peromyscus models can now be more fully exploited due to the emerging genetic (full linkage map), genomic (genomes of four stocks have been sequenced) and reproductive resources.

Lack of association between common polymorphisms of epidermal growth factor receptors and nonsyndromic cleft lip with or without cleft palate

OBJECTIVES

Nonsyndromic cleft lip with or without cleft palate (CL/P) is a frequent craniofacial malformation with a complex aetiology. Since the first report of an association between DNA sequence variants at the transforming growth factor alpha gene (TGFA) and nonsyndromic oral clefts, several studies have been carried out, which have produced conflicting results. Overall, TGFA is considered as a genetic clefting modifier in humans. Murine models indicate that the Tgfa product (tgfalpha), as well as its receptor (Egfr), actively participates in palate development. Notably, Egfr null mice showed an increased incidence in orofacial clefts. In the present study, genes which code for subunits of epidermal growth factor receptors (EGFRs) have been considered as candidate genes for CL/P.

METHODS

A family based investigation was performed using a sample of 239 case/parent triads. The aim was to test for an allelic association between common non-synonymous polymorphisms in EGFR genes and CL/P.

RESULTS AND CONCLUSION

The results did not suggest any evidence of a link between the investigated polymorphisms and CL/P, however the involvement of different polymorphisms or mutations in such genes cannot be excluded.

Genomic imprinting of Dopa decarboxylase in heart and reciprocal allelic expression with neighboring Grb10

By combining a tissue-specific microarray screen with mouse uniparental duplications, we have identified a novel imprinted gene, Dopa decarboxylase (Ddc), on chromosome 11. Ddc_exon1a is a 2-kb transcript variant that initiates from an alternative first exon in intron 1 of the canonical Ddc transcript and is paternally expressed in trabecular cardiomyocytes of the embryonic and neonatal heart. Ddc displays tight conserved linkage with the maternally expressed and methylated Grb10 gene, suggesting that these reciprocally imprinted genes may be coordinately regulated. In Dnmt3L mutant embryos that lack maternal germ line methylation imprints, we show that Ddc is overexpressed and Grb10 is silenced. Their imprinting is therefore dependent on maternal germ line methylation, but the mechanism at Ddc does not appear to involve differential methylation of the Ddc_exon1a promoter region and may instead be provided by the oocyte mark at Grb10. Our analysis of Ddc redefines the imprinted Grb10 domain on mouse proximal chromosome 11 and identifies Ddc_exon1a as the first example of a heart-specific imprinted gene.

Assessment and disease comparisons of hybrid developmental defects

Rodents of the genus Peromyscus are among the most common North American mammals. Crosses between natural populations of two of these species, P. maniculatus (BW) and P. polionotus (PO), produce parent-of-origin effects on growth and development. BW females mated to PO males produce growth-retarded offspring. In contrast, PO females mated to BW males produce overgrown but dysmorphic conceptuses. Variation in imprinted loci and control of genomic imprinting appear to underlie the hybrid effects. Prior morphological and genetic analyses have focused on placental and post-natal growth. Here, we assess the frequency and scope of embryonic defects. The most frequent outcome of the PO x BW cross is death prior to embryonic day 13. Conceptuses lacking an embryo proper are also observed as in gestational trophoblast disease. Among the common embryonic phenotypes described and tabulated are edema, blood vessel enlargement/hemorrhaging, macroglossia, retention of nucleated erythrocytes, placentomegaly. We investigate expression of loci known to be mis-regulated in human growth/placental disorders and/or mouse knockouts with similar phenotypes. These loci are Igf2, Cdkn1c, Grb10, Gpc3, Phlda2 and Rb1. All exhibited significant differences in either placental or embryonic expression levels at one or more of the three timepoints examined. The data underscore the importance of placental gene expression on embryonic defects. We suggest that the hybrid defects offer a novel system to understand how natural allelic combinations interact to produce disease phenotypes. We propose that such interactions and their resulting epimutations may similarly underlie the phenotypic and causal heterogeneity seen in many human diseases.

Assessment and treatment of short stature in pediatric patients with chronic kidney disease: a consensus statement

Growth failure is a clinically important issue in children with chronic kidney disease (CKD) and is associated with significant morbidity and mortality. Many factors contribute to impaired growth in these children, including abnormalities in the growth hormone (GH)-insulin-like growth factor-I (IGF-I) axis, malnutrition, acidosis, and renal bone disease. The management of growth failure in children with CKD is complicated by the presence of other disease-related complications requiring medical intervention. Despite evidence of GH efficacy and safety in this population, some practitioners and families have been reluctant to institute GH therapy, citing an unwillingness to comply with daily injections, reimbursement difficulties, or impending renal transplantation. Suboptimal attention to growth failure management may be further compounded by a lack of clinical guidelines for the appropriate assessment and treatment of growth failure in these children. This review of growth failure in children with CKD concludes with an algorithm developed by members of the consensus committee, outlining their recommendations for appropriate steps to improve growth and overall health outcomes in children with CKD.

Hypoglycaemia and Russell-Silver syndrome

AIM

To determine both the incidence and aetiology of chronic hypoglycaemia in symptomatic children with Russell-Silver syndrome (RSS) during the first four years of life.

STUDY DESIGN

Twenty-four children with RSS under the age of 4 years, who had either clinical symptoms of hypoglycaemia or previous evidence of biochemically documented hypoglycaemia, were admitted to hospital for 48 hours to perform a 24-h cortisol/glucose profile and a diagnostic fast in those who did not develop spontaneous hypoglycaemia. A dietary assessment was also performed. Glucose profile was assessed in 20 children and cortisol profile in 16; combined glucose and cortisol profile in 15 children. Eight children had a diagnostic fast. Mean chronological age at time of assessment was 2.2 +/- 0.8 years (range 1.1-3.9 years).

RESULTS

Ten of 24 children had previously been documented as having hypoglycaemia. Seven of 12 patients were growth hormone (GH) insufficient after a glucagon test. Their feeding pattern was described as 'poor and picky eaters' in all, seven requiring nasogastric tube feeding. The mean spontaneous energy intake (n = 8) was 56 +/- 19.6 kcal/kg/day (range 38-90). Nocturnal sweating was the commonest symptom (23.96%), followed by irritability (11.46%), tantrums (7.29%), pallor and shakiness (3.13%). The glucose profile in seven children showed hypoglycaemia but only four were symptomatic. None of the children was cortisol deficient. The mean period of fasting was 11.8 +/- 4 hours (range 3-18 h). No metabolic/hormonal abnormality, with the exception of GH insufficiency, was detected at the time of hypoglycaemia.

CONCLUSION

Children with RSS are prone to develop spontaneous hypoglycaemia especially if they are not fed both frequently and regularly. The most likely explanation is accelerated starvation and/or GH insufficiency. We suggest guidelines to minimise hypoglycaemia in these children.

Living with achondroplasia in an average-sized world: an assessment of quality of life

Mutations in the gene encoding fibroblast growth factor receptor 3 cause achondroplasia, the most common form of inherited skeletal dysplasia. Although there are more than 10,000 individuals with achondroplasia living in the United States, there has been little study of their quality of life (QOL). For this study, surveys were collected from 189 individuals affected with achondroplasia (ACH) and 136 unaffected first-degree relatives (FDRs) of affected individuals. Individuals affected with achondroplasia had lower annual income, less education, and were less likely to be married than FDRs. They also differed significantly in their perceptions of achondroplasia, with FDRs believing that achondroplasia is a more serious condition. Total QOL indices and indices in each of four QOL subdomains were significantly lower in affected individuals than in relatives. When controlling for demographic characteristics and affected status, having lower self-esteem scores and perceiving achondroplasia as more serious were the independent factors most highly associated with lower QOL. A qualitative analysis of open responses to questions about the advantages and disadvantages of achondroplasia revealed that individuals were as likely to cite disadvantages relating to social barriers as they were to cite those relating to health and functioning. We interpret the low QOL scores to reflect the social challenges that individuals with achondroplasia regularly experience in the average-sized world. Genetics professionals should consider sources of lower QOL for affected individuals in their counseling sessions to acknowledge the relative importance of non-medical contributions.

Gastrointestinal complications of Russell-Silver syndrome: a pilot study

Russell-Silver syndrome (RSS) is a genetic syndrome with clinical manifestations of intrauterine and postnatal growth retardation, normal head circumference, body asymmetry, and distinctive facial appearance. We followed an infant diagnosed with RSS who had occurrence of multiple gastrointestinal complications. Although there are a number of published reports describing gastrointestinal problems associated with RSS, specific gastrointestinal diseases have not been recognized as major features. We hypothesize that gastrointestinal complications may be more frequent in RSS cases than previously reported. To address our hypothesis, we developed a pilot study of RSS cases to identify and characterize associated gastrointestinal complications. Surveys were distributed by MAGIC, a support group for individuals with RSS. Surveys included information on the objective and subjective characteristics used to diagnose RSS, as well as descriptions of gastrointestinal problems. Completed surveys were returned on 135 individuals. We used strict diagnostic guidelines to determine affected status of children reported in our survey. Of the 135 surveys completed, 65 were determined to have clear-cut RSS. The diagnoses were made without knowledge of the gastrointestinal symptoms of any of the subjects. Of the 65 subjects with "clear cut" RSS, 50 (77%) had gastrointestinal symptoms. Major specific symptoms included gastroesophageal reflux disease (34%), esophagitis (25%), food aversion (32%), and failure to thrive (63%). A common theme in gastrointestinal complications of RSS is significant gastroesophageal reflux that includes esophagitis and food aversion. Results of this survey suggest that there is an association of gastrointestinal complications with RSS that should be addressed in diagnosis as well as management protocols for children with this condition.

Familial reciprocal translocation t(7;16) associated with maternal uniparental disomy 7 in a Silver-Russell patient

We present the case of a maternal heterodisomy for chromosome 7 in the daughter of a t(7;16)(q21;q24) reciprocal translocation carrier. The proband was referred to the hospital for growth retardation and minor facial dysmorphism without mental retardation. A diagnosis of Silver-Russell syndrome was suspected. Chromosomal analysis documented a 46,XX,t(7;16)(q21;q24)mat chromosome pattern. Microsatellite analysis showed a normal biparental inheritance of chromosome 16 but a maternal heterodisomy of chromosome 7. Occurrence of uniparental disomy (UPD) is a well-recognized consequence of chromosomal abnormalities that increase the rate of meiotic nondisjunction, mainly Robertsonian translocations and supernumerary chromosomes. Although reciprocal translocations should, theoretically, be also at increased risk of UPD, only three cases have been reported so far. However, because the association between uniparental disomy and reciprocal translocation may exist with an underestimated frequency, prenatal diagnosis is recommended when clinically relevant chromosomes for UPD are involved.

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.

Perceived versus measured height. Which is the stronger predictor of psychosocial functioning?

The relationship between perceptions versus measured height and children's psychosocial adaptation in a sample of medically referred youth with short stature was investigated. All children referred for a growth evaluation to one regional pediatric endocrinology clinic received a psychosocial screening assessment as a routine component of their initial visit. Data were collected for patients ages 4-18 years (n = 620) with heights ranging from -4.0 to -1.1 SD for age- and gender-adjusted population norms. Patients (8 years and older) and in all cases a parent/guardian served as informant through paper-and-pencil questionnaires. Both children and parents overestimated the child's height. Overestimations of height were associated with greater patient and parent satisfaction with stature. Perceived height was more strongly associated with psychosocial adaptation than was measured height. Clinical management decisions designed to enhance patient quality of life by increasing projected adult height through hormonal interventions should take into account both measured and perceived patient height.

Imprinting of human GRB10 and its mutations in two patients with Russell-Silver syndrome

Documentation of maternal uniparental disomy of chromosome 7 in 10% of patients with Russell-Silver syndrome (RSS), characterized by prenatal and postnatal growth retardation and dysmorphic features, has suggested the presence of an imprinted gene on chromosome 7 whose mutation is responsible for the RSS phenotype. Human GRB10 on chromosome 7, a homologue of the mouse imprinted gene Grb10, is a candidate, because GRB10 has a suppressive effect on growth, through its interaction with either the IGF-I receptor or the GH receptor, and two patients with RSS were shown to have a maternally derived duplication of 7p11-p13, encompassing GRB10. In the present study, we first demonstrated that the GRB10 gene is also monoallelically expressed in human fetal brain tissues and is transcribed from the maternally derived allele in somatic-cell hybrids. Hence, human GRB10 is imprinted. A mutation analysis of GRB10 in 58 unrelated patients with RSS identified, within the N-terminal domain of the protein, a P95S substitution in two patients with RSS. In these two cases, the mutant allele was inherited from the mother. The fact that monoallelic GRB10 expression was observed from the maternal allele in this study suggests but does not prove that these maternally transmitted mutant alleles contribute to the RSS phenotype.

Zac1 (Lot1), a potential tumor suppressor gene, and the gene for epsilon-sarcoglycan are maternally imprinted genes: identification by a subtractive screen of novel uniparental fibroblast lines

Imprinted genes are expressed from one allele according to their parent of origin, and many are essential to mammalian embryogenesis. Here we show that the epsilon-sarcoglycan gene (Sgce) and Zac1 (Lot1) are both paternally expressed imprinted genes. They were identified in a subtractive screen for imprinted genes using a cDNA library made from novel parthenogenetic and wild-type fibroblast lines. Sgce is a component of the dystrophin-sarcoglycan complex, Zac1 is a nuclear protein inducing growth arrest and/or apoptosis, and Zac1 is a potential tumor suppressor gene. Sgce and Zac1 are expressed predominantly from their paternal alleles in all adult mouse tissues, except that Zac1 is biallelic in the liver and Sgce is weakly expressed from the maternal allele in the brain. Sgce and Zac1 are broadly expressed in embryos, with Zac1 being highly expressed in the liver primordium, the umbilical region, and the neural tube. Sgce, however, is strongly expressed in the allantoic region on day 9.5 but becomes more widely expressed throughout the embryo by day 11.5. Sgce is located at the proximal end of mouse chromosome 6 and is a candidate gene for embryonic lethality associated with uniparental maternal inheritance of this region. Zac1 maps to the proximal region of chromosome 10, identifying a new imprinted locus in the mouse, homologous with human chromosome 6q24-q25. In humans, unipaternal disomy for this region is associated with fetal growth retardation and transient neonatal diabetes mellitus. In addition, loss of expression of ZAC has been described for a number of breast and ovarian carcinomas, suggesting that ZAC is a potential tumor suppressor gene.

Should we treat children with idiopathic short stature?

The use of growth hormone (GH) to treat short children who are clearly GH-deficient is now well accepted. However, GH treatment of short children who have no currently recognizable abnormalities in their GH-insulin-like growth factor I axis remains controversial. Whether such children with so-called idiopathic short stature (ISS) should be treated with GH was the subject of an international workshop held in St.-Paul-de-Vence, France, in April 1999. This article summarizes the issues discussed at the workshop, including the definition of ISS, ethical and health-economic aspects of treatment, results from clinical trials and surveillance studies, and the use of prediction models in aiding treatment decisions.

Towards better decision making in growth hormone therapy

Controlled clinical trials are not always possible or warranted. Other sources of data include observational studies, meta-analyses, expert opinions, subjective judgements, and mathematical/statistical models developed from large databases. Decision analysis is presented as a preferred methodology for analysis in situations of uncertainty, in combination with cost-benefit and cost-effectiveness analyses. Special emphasis is given to quality-of-life considerations in growth hormone (GH) therapy and ways to measure it and express patient preferences.