Case report: A novel de novo IGF2 missense variant in a Finnish patient with Silver-Russell syndrome

Silver-Russell syndrome (SRS, OMIM 180860) is a rare imprinting disorder characterized by intrauterine and postnatal growth restriction, feeding difficulties in early childhood, characteristic facial features, and body asymmetry. The molecular cause most commonly relates to hypomethylation of the imprinted 11p15.5 IGF2/H19 domain but remains unknown in about 40% of the patients. Recently, heterozygous paternally inherited pathogenic variants in IGF2, the gene encoding insulin-like growth factor 2 (IGF2), have been identified in patients with SRS. We report a novel de novo missense variant in IGF2 (c.122T > G, p.Leu41Arg) on the paternally derived allele in a 16-year-old boy with a clinical diagnosis of SRS. The missense variant was identified by targeted exome sequencing and predicted pathogenic by multiple in silico tools. It affects a highly conserved residue on a domain that is important for binding of other molecules. Our finding expands the spectrum of disease-causing variants in IGF2. Targeted exome sequencing is a useful diagnostic tool in patients with negative results of common diagnostic tests for SRS.

Pericardial Constriction and Myocardial Restriction in Pediatric Mulibrey Nanism: A Complex Disease With Diastolic Dysfunction

Background

Mulibrey nanism (MUL) is a rare condition with profound growth delay. Congestive heart failure is a major determinant of prognosis. The aim was to delineate pericardial constriction and myocardial functional abnormalities in a pediatric MUL sample.

Methods

A total of 23 MUL patients and 23 individually sex- and age-matched healthy control subjects were prospectively assessed in a cross-sectional study with echocardiography.

Results

Clinical signs of heart failure were present in 7 MUL patients, with severe congestive heart failure in 2. Significant diastolic dysfunction, mainly related to constriction, was found in MUL patients without pericardiectomy (N = 18)—septal bounce, pronounced hepatic vein atrial reversal and right heart inflow–outflow variations, and decreased inferior vena cava collapse during respiration. The appearance of the pericardium was not different from that of control subjects. Longitudinal diastolic myocardial velocities were similar to those in control subjects, suggesting an absence of significant myocardial restriction. Right ventricular free wall longitudinal systolic strain and bilateral longitudinal myocardial systolic velocities were decreased in MUL patients, indicating mild biventricular systolic dysfunction. Myocardial motion abnormalities and persistent congestive heart failure were common (in 3 of 6) in MUL patients with a history of pericardiectomy. Cardiac dimensions were similar between MUL patients and control subjects when adjusting for body size, except for smaller biventricular volumes.

Conclusions

MUL disease presents with significant constriction-related diastolic dysfunction and mild bilateral systolic dysfunction. Constriction–restriction assessments during follow-up could be of benefit in decision-making regarding pericardiectomy in MUL disease. Myocardial abnormalities were prevalent among MUL patients who had undergone pericardiectomy and are consistent with progression of myocardial disease in a significant proportion of patients.

TRIM37 prevents formation of centriolar protein assemblies by regulating Centrobin

TRIM37 is an E3 ubiquitin ligase mutated in Mulibrey nanism, a disease with impaired organ growth and increased tumor formation. TRIM37 depletion from tissue culture cells results in supernumerary foci bearing the centriolar protein Centrin. Here, we characterize these centriolar protein assemblies (Cenpas) to uncover the mechanism of action of TRIM37. We find that an atypical de novo assembly pathway can generate Cenpas that act as microtubule-organizing centers (MTOCs), including in Mulibrey patient cells. Correlative light electron microscopy reveals that Cenpas are centriole-related or electron-dense structures with stripes. TRIM37 regulates the stability and solubility of Centrobin, which accumulates in elongated entities resembling the striped electron dense structures upon TRIM37 depletion. Furthermore, Cenpas formation upon TRIM37 depletion requires PLK4, as well as two parallel pathways relying respectively on Centrobin and PLK1. Overall, our work uncovers how TRIM37 prevents Cenpas formation, which would otherwise threaten genome integrity.

Restriction of lung volumes but normal function of pulmonary tissue in mulibrey nanism

BACKGROUND

Mulibrey nanism (MUL) is a rare growth restriction disorder with multiple organ manifestations caused by genetic defects affecting the TRIM37 protein. A perimyocardial heart disease is the most serious manifestation. Many MUL children appear to suffer from airway obstruction related to infection or exercise, prompting use of inhaled therapies. Asthma medication is continued up to adolescence or even to adulthood due to persisting of symptoms. The pulmonary pathophysiology has previously not been evaluated in any MUL cohort.

METHODS

Thirty three finnish MUL patients (median age 20 years) were investigated with several lung function tests: spirometry with bronchodilatation test, single-breath diffusing capacity for carbon monoxide, single-breath lung volume measurements with helium dilution, and thoracic gas volume, airway resistance and specific conductance measurements with a body plethysmograph. As MUL typically affects body proportions, all variables were compared with reference values and with predicted values calculated from sitting height.

RESULTS

Total lung capacity and forced vital capacity were markedly reduced (total lung capacity [TLC] and forced vital capacity [FVC], P < .001, 51%-63% of predicted) and also forced expiratory volume in the first second was reduced (FEV1; P < .001, 47%-57%). No signs of airway obstruction was seen (normal FEV1/FVC and specific airway conductance SGaw). Diffusing capacity (DLCO) was decreased (P < .001, 60%-67%) but when related to alveolar volume it was increased (DLCO/VA, P < .001, 130%-148%). Bronchodilatation suggesting active asthma (FEV1 change ≥12% and ≥​​200 mL) was found only in one patient.

CONCLUSION

MUL patients typically have volume restriction of the lungs, but function of the pulmonary tissue remains intact. Evidence of asthma in lung function testing at adult age is rare.

Rare Variants in Genes Linked to Appetite Control and Hypothalamic Development in Early-Onset Severe Obesity

Context: The hypothalamic circuit has an essential role in the regulation of appetite and energy expenditure. Pathogenic variants in genes involved in the hypothalamic leptin-melanocortin pathway, including melanocortin-4-receptor (MC4R), have been associated with monogenic obesity. Objective: To determine the rate and spectrum of rare variants in genes involved in melanocortin pathway or hypothalamic development in patients with severe early-onset obesity (height-adjusted weight >60% before age 10 years). Methods: We used a custom-made targeted exome sequencing panel to assess peripheral blood DNA samples for rare (minor allele frequency <0.5%), pathogenic/likely pathogenic variants in 24 genes related to the hypothalamic circuit in 92 subjects (51% males, median age 13.7 years) with early-onset severe obesity (median body mass index (BMI) Z-score + 4.0). Results: We identified a novel frameshift deletion in MC4R (p.V103Afs5^*) in two unrelated patients and a previously reported MC4R variant (p.T112M) in one patient. In addition, we identified rare heterozygous missense variants in ADCY3 (p.G1110R), MYT1L (p.R807Q), ISL1 (p.I347F), LRP2 (p.R2479I, and p.N3315S) and a hemizygous missense variant in GRPR (p.L87M) (each in one patient), possibly contributing to the obesity phenotype in these patients. Altogether 8 % (7/92) of the subjects had rare pathogenic/likely pathogenic variants in the studied genes. Conclusions: Rare genetic variants within the hypothalamic circuit are prevalent and contribute to the development of severe early-onset obesity. Targeted exome sequencing is useful in identifying affected subjects. Further studies are needed to evaluate the variants' clinical significance and to define optimal treatment.

Premature ovarian insufficiency and early depletion of the ovarian reserve in the monogenic Mulibrey nanism disorder

STUDY QUESTION

What is the timing of onset and clinical course of premature ovarian insufficiency (POI) in patients with Mulibrey nanism (MUL), a monogenic disorder caused by mutations of the peroxisomal TRIM37 gene?

SUMMARY ANSWER

The number of ovarian follicles is highly reduced already in infant and young MUL girls and the majority of them will have early depletion of follicles resulting in clinical and biochemical signs of POI.

WHAT IS KNOWN ALREADY

Both female and male patients with MUL show failure of sexual maturation, signs of hypogonadism and infertility.

STUDY DESIGN, SIZE, DURATION

We studied the gonadal function, pubertal development and ovarian reserve in 33 MUL patients aged 5.1-47.3 years (median age 22.3) at the end of observation. The patients were followed between 2004 and 2014 and 19 pubertal or postpubertal patients were enrolled in a cross-sectional study.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The period of postnatal activation of the hypothalamic-pituitary-gonadal axis (minipuberty), pubertal development and menstrual history were assessed longitudinally. The cross-sectional study included gynecological examination, analysis of reproductive hormones and ultrasonography with evaluation of ovarian volume and antral follicle count.

MAIN RESULTS AND THE ROLE OF CHANCE

Infant girls experienced a transient minipuberty with a high FSH surge. In childhood, gonadotropins were normal or slightly elevated but began to rise to hypergonadotropic levels in prepuberty. Anti-Müllerian hormone (AMH) levels remained undetectable or low throughout childhood. The onset of puberty occurred spontaneously and the median age at menarche was 12.5 years. Of the patients, 54% never attained regular menses and 10 years from menarche, only 8% of the women menstruated regularly. In the cross-sectional study, none of the patients had normal ovarian morphology under ultrasonography. Ovaries were hypoplastic and 82% had no or fewer than two visible antral follicles. AMH levels were undetectable in the vast majority (89%).

LIMITATIONS, REASONS FOR CAUTION

The Finnish MUL patients genotypically form a homogenous group and therefore it is possible, that different TRIM37 mutations lead to different hypogonadal phenotypes. However, to date there is no known genotype-phenotype correlation in MUL.

WIDER IMPLICATIONS OF THE FINDINGS

In MUL, AMH is a useful marker of ovarian function. MUL should be added to the list of syndromes associated with POI and correspondingly, TRIM37 should be added to the list of genes associated with POI. To our knowledge, TRIM37 is the first known gene coding for a peroxisomal membrane protein associated with female gonadal failure and infertility. Elucidating the role of syndromic genes in reproduction may aid in a greater understanding of ovarian biology.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Finnish Foundation for Pediatric Research, Finska Läkaresällskapet, the Sigrid Jusélius Foundation and Helsinki University Hospital Research Funds. The authors declare no conflicts of interest.

TRIAL REGISTRATION NUMBER

Not applicable.

Testicular Function and Bone in Young Men with Severe Childhood-Onset Obesity

BACKGROUND

Previous studies suggest increased risk for hypoandrogenism and fractures in men with obesity. We aimed to describe the effects of severe childhood-onset obesity on the cross talk between metabolic state, testes, and skeleton at late puberty.

METHODS

A cohort of adolescent and young adult males with severe childhood-onset obesity (n = 21, mean age 18.5 years) and an age-matched control group were assessed for testicular hormones and X-ray absorptiometry-derived bone mass.

RESULTS

Current median body mass indexes for the obese and control subjects were 37.4 and 22.9. Severe early-onset obesity manifested with lower free testosterone (median [interquartile range] 244 [194-332] vs. 403 [293-463] pmol/L, p = 0.002). Lower insulin-like 3 (1.02 [0.82-1.23] vs. 1.22 [1.01-1.46] ng/mL, p = 0.045) and lower ratio of testosterone to luteinizing hormone (2.81 [1.96-3.98] vs. 4.10 [3.03-5.83] nmol/IU, p = 0.008) suggested disrupted Leydig cell function. The degree of current obesity inversely correlated with free testosterone (τ = -0.516, p = 0.003), which in turn correlated positively with bone area at all measurement sites in males with childhood-onset obesity.

CONCLUSIONS

Severe childhood-onset obesity is associated with impaired Leydig cell function in young men and lower free testosterone may contribute to impaired skeletal characteristics.

Hypomethylation of HOXA4 promoter is common in Silver-Russell syndrome and growth restriction and associates with stature in healthy children

Silver-Russell syndrome (SRS) is a growth retardation syndrome in which loss of methylation on chromosome 11p15 (11p15 LOM) and maternal uniparental disomy for chromosome 7 [UPD(7)mat] explain 20–60% and 10% of the syndrome, respectively. To search for a molecular cause for the remaining SRS cases, and to find a possible common epigenetic change, we studied DNA methylation pattern of more than 450 000 CpG sites in 44 SRS patients. Common to all three SRS subgroups, we found a hypomethylated region at the promoter region of HOXA4 in 55% of the patients. We then tested 39 patients with severe growth restriction of unknown etiology, and found hypomethylation of HOXA4 in 44% of the patients. Finally, we found that methylation at multiple CpG sites in the HOXA4 promoter region was associated with height in a cohort of 227 healthy children, suggesting that HOXA4 may play a role in regulating human growth by epigenetic mechanisms.

Two missense mutations in KCNQ1 cause pituitary hormone deficiency and maternally inherited gingival fibromatosis

Familial growth hormone deficiency provides an opportunity to identify new genetic causes of short stature. Here we combine linkage analysis with whole-genome resequencing in patients with growth hormone deficiency and maternally inherited gingival fibromatosis. We report that patients from three unrelated families harbor either of two missense mutations, c.347G>T p.(Arg116Leu) or c.1106C>T p.(Pro369Leu), in KCNQ1, a gene previously implicated in the long QT interval syndrome. Kcnq1 is expressed in hypothalamic GHRH neurons and pituitary somatotropes. Co-expressing KCNQ1 with the KCNE2 β-subunit shows that both KCNQ1 mutants increase current levels in patch clamp analyses and are associated with reduced pituitary hormone secretion from AtT-20 cells. In conclusion, our results reveal a role for the KCNQ1 potassium channel in the regulation of human growth, and show that growth hormone deficiency associated with maternally inherited gingival fibromatosis is an allelic disorder with cardiac arrhythmia syndromes caused by KCNQ1 mutations.

Trim37-deficient mice recapitulate several features of the multi-organ disorder Mulibrey nanism

Mulibrey nanism (MUL) is a rare autosomal recessive multi-organ disorder characterized by severe prenatal-onset growth failure, infertility, cardiopathy, risk for tumors, fatty liver, and type 2 diabetes. MUL is caused by loss-of-function mutations in TRIM37, which encodes an E3 ubiquitin ligase belonging to the tripartite motif (TRIM) protein family and having both peroxisomal and nuclear localization. We describe a congenic Trim37 knock-out mouse (Trim37^−/−) model for MUL. Trim37^−/− mice were viable and had normal weight development until approximately 12 months of age, after which they started to manifest increasing problems in wellbeing and weight loss. Assessment of skeletal parameters with computer tomography revealed significantly smaller skull size, but no difference in the lengths of long bones in Trim37^−/− mice as compared with wild-type. Both male and female Trim37^−/− mice were infertile, the gonads showing germ cell aplasia, hilus and Leydig cell hyperplasia and accumulation of lipids in and around Leydig cells. Male Trim37^−/− mice had elevated levels of follicle-stimulating and luteinizing hormones, but maintained normal levels of testosterone. Six-month-old Trim37^−/− mice had elevated fasting blood glucose and low fasting serum insulin levels. At 1.5 years Trim37^−/− mice showed non-compaction cardiomyopathy, hepatomegaly, fatty liver and various tumors. The amount and morphology of liver peroxisomes seemed normal in Trim37^−/− mice. The most consistently seen phenotypes in Trim37^−/− mice were infertility and the associated hormonal findings, whereas there was more variability in the other phenotypes observed. Trim37^−/− mice recapitulate several features of the human MUL disease and thus provide a good model to study disease pathogenesis related to TRIM37 deficiency, including infertility, non-alcoholic fatty liver disease, cardiomyopathy and tumorigenesis.

Summary: A congenic Trim37-deficient mouse model recapitulates several features of the human disorder Mulibrey nanism, and thus provides a good model to study disease pathogenesis related to TRIM37 deficiency.

Bone Characteristics and Their Determinants in Adolescents and Young Adults with Early-Onset Severe Obesity

Childhood obesity is associated with compromised bone health. We studied bone characteristics and their determinants in obese young adults. The study included 68 subjects with early-onset severe obesity and 73 normal-weight controls. Data on physical activity (PA), diet and smoking were collected. Bone characteristics were measured using peripheral QCT. The obese and control subjects were similar in age (mean 19.6 ± 2.6 years) and height but BMIs differed (39.7 and 22.6 kg/m(2)). A clustering of unhealthy lifestyles was marked: Obese subjects reported less supervised PA in childhood, adolescence and currently (p < 0.03) and were more likely to smoke (p = 0.005), and had a lower healthy eating index (HEI) (p = 0.007) but similar alcohol consumption compared with controls. In obese women, all crude bone characteristics were higher than in controls; in men, the differences were smaller. Associations of lifestyle factors with bone characteristics were tested using partial correlations. Independently of BMI, supervised PA in adolescence and alcohol consumption were related positively to bone characteristics in both groups. HEI associated positively with bone characteristics only in controls, while smoking was a positive determinant of bone characteristics only in obese subjects. The multivariate model showed that the contribution of lifestyle factors to bone characteristics was minimal compared with BMI. Early-onset obesity is accompanied by poor dietary quality, sedentary lifestyle, and more frequent smoking, but the overall contribution of these lifestyle factors to bone strength is limited. Bone strength is more likely to be compromised in men and in unloaded bone sites in subjects with early-onset severe obesity. The impact of obesity-related endocrine changes on bone characteristics need to be evaluated in future studies.

Low Copy Number of the AMY1 Locus Is Associated with Early-Onset Female Obesity in Finland

Background

The salivary α-amylase locus (AMY1) is located in a highly polymorphic multi allelic copy number variable chromosomal region. A recent report identified an association between AMY1 copy numbers and BMI in common obesity. The present study investigated the relationship between AMY1 copy number, BMI and serum amylase in childhood-onset obesity.

Patients

Sixty-one subjects with a history of childhood-onset obesity (mean age 19.1 years, 54% males) and 71 matched controls (19.8 yrs, 45% males) were included. All anthropometric measures were greater in the obese; their mean BMI was 40 kg/m² (range 25-62 kg/m²) compared with 23 kg/m² in the controls (15-32 kg/m²).

Results

Mean AMY1 copy numbers did not differ between the obese and control subjects, but gender differences were observed; obese men showed the highest and obese women the lowest number of AMY1 copies (p=0.045). Further, only in affected females, AMY1 copy number correlated significantly with whole body fat percent (r=-0.512, p=0.013) and BMI (r=-0.416, p=0.025). Finally, a clear linear association between AMY1 copy number and serum salivary amylase was observed in all subgroups but again differences existed between obese males and females.

Conclusions

In conclusion, our findings suggest that AMY1 copy number differences play a role in childhood-onset obesity but the effect differs between males and females. Further studies in larger cohorts are needed to confirm these observations.

Suppressed bone turnover in obesity: a link to energy metabolism? A case-control study

CONTEXT

Observations in rodents suggest that osteocalcin (OC) participates in glucose metabolism. Based on human studies, it remains unclear whether circulating OC is simply a bone turnover marker (BTM) or also a mediator in interactions between the skeleton and glucose homeostasis.

OBJECTIVE

The objective of the study was to determine the responses of BTMs, including OC, to oral glucose tolerance test (OGTT) in a case-control setting.

DESIGN AND PATIENTS

Thirty-four normoglycemic young adults [mean age 19 y (SD 2.3)] with severe childhood-onset obesity and their gender- and age-matched nonobese controls underwent a standard 2-hour OGTT.

MAIN OUTCOME MEASURES

Glucose, insulin, and six BTMs including total and carboxylated OC (cOC) were determined at baseline and at 30, 60, 90, and 120 minutes during OGTT.

RESULTS

The obese and control subjects were similar in height; the mean body mass indices were 40.4 and 21.9 kg/m(2), respectively. The homeostasis model assessment index was 2.7 times greater in the obese subjects. All BTMs, except bone-specific alkaline phophatase, were lower in the obese subjects compared with the controls: the differences at baseline were 40%, 35%, 17%, 31%, and 32% for N-terminal propeptides of type I collagen, cross-linked telopeptides of type I collagen, tartrate-resistant acid phosphatase, total OC, and carboxylated OC (P < .05 for all) after adjusting for whole-body bone area. All BTMs decreased during OGTT. The relative values for the OGTT responses for total, but not for cOC (measured as area under the curve) differed between the two groups (P = .029 and P = .139, respectively): the decrease in total OC during the OGTT was less pronounced in the obese subjects. Responses in other BTMs were similar between the groups. No associations were observed between glucose metabolism and OCs during OGTT with linear regression.

CONCLUSIONS

Bone turnover markers were substantially lower in obese subjects compared with controls. Total OC and cOC showed less pronounced decrease during the OGTT in obese subjects compared with controls, whereas other BTMs responded similarly in the two groups. The role of OC, if anything, in glucose homeostasis is indirect and may be mediated via other factors than glucose or insulin.

Differentially methylated regions in maternal and paternal uniparental disomy for chromosome 7

DNA methylation is a hallmark of genomic imprinting and differentially methylated regions (DMRs) are found near and in imprinted genes. Imprinted genes are expressed only from the maternal or paternal allele and their normal balance can be disrupted by uniparental disomy (UPD), the inheritance of both chromosomes of a chromosome pair exclusively from only either the mother or the father. Maternal UPD for chromosome 7 (matUPD7) results in Silver-Russell syndrome (SRS) with typical features and growth retardation, but no gene has been conclusively implicated in SRS. In order to identify novel DMRs and putative imprinted genes on chromosome 7, we analyzed eight matUPD7 patients, a segmental matUPD7q31-qter, a rare patUPD7 case and ten controls on the Infinium HumanMethylation450K BeadChip with 30 017 CpG methylation probes for chromosome 7. Genome-scale analysis showed highly significant clustering of DMRs only on chromosome 7, including the known imprinted loci GRB10, SGCE/PEG10, and PEG/MEST. We found ten novel DMRs on chromosome 7, two DMRs for the predicted imprinted genes HOXA4 and GLI3 and one for the disputed imprinted gene PON1. Quantitative RT-PCR on blood RNA samples comparing matUPD7, patUPD7, and controls showed differential expression for three genes with novel DMRs, HOXA4, GLI3, and SVOPL. Allele specific expression analysis confirmed maternal only expression of SVOPL and imprinting of HOXA4 was supported by monoallelic expression. These results present the first comprehensive map of parent-of-origin specific DMRs on human chromosome 7, suggesting many new imprinted sites.

[Update on Current Care guidelines: obesity (children)]

Childhood obesity is an increasing health problem. There may be possibilities to prevent obesity in childhood, and efficient interventions to treat obese children have been published. Local and regional strategies to prevent and to treat childhood obesity are needed.

Testicular failure and male infertility in the monogenic Mulibrey nanism disorder

CONTEXT

Few monogenic mutations causing human male infertility have been identified to date.

OBJECTIVE

We studied pubertal development and fecundity in males with Mulibrey nanism (MUL) caused by mutations in the TRIM37 gene.

DESIGN, SETTING, AND PATIENTS

Twenty-eight male MUL patients of the Finnish national cohort aged 8.7 to 50.0 yr (median age, 28.8) at the end of observation were followed for 10 yr beginning from 2000-2001.

MAIN OUTCOME MEASURES

Clinical characteristics, reproductive hormone levels, semen quality, and testicular histology were assessed.

RESULTS

The external genital phenotype was normal. In childhood and prepuberty, serum levels of FSH, LH, testosterone (T), and inhibin B were normal. Puberty started spontaneously at a median age of 12.6 yr (range, 11.1-15.0), and FSH, LH, T, and inhibin B levels increased adequately until midpuberty. Thereafter, testicular growth and virilization proceeded slowly. Concomitantly, FSH, and to a lesser extent LH, showed a progressive increase to hypergonadotropic levels in all patients, whereas inhibin B decreased and T leveled off. Testicular size was small (median volume, 8.7 ml; range, 3.5-18.3 ml in adults). All semen samples showed severe oligoasthenozoospermia or azoospermia. None of the patients had a history of spontaneous fertility, but four men had undergone infertility treatment, which in one case was successful. All histological MUL samples showed varying degrees of degeneration.

CONCLUSIONS

All adult MUL males have a unique disorder of testicular function with small testes, elevated FSH and LH, and low inhibin B. In MUL, mutations in TRIM37 lead to disturbance of sexual maturation, and fertility is severely compromised. Thus, TRIM37 is a novel gene causing male infertility.

Methylation of H19 and its imprinted control region (H19 ICR1) in Müllerian aplasia

Severe hypomethylation of the H19 imprinted control region (ICR1) in two patients with Silver-Russell syndrome (SRS) who have genital malformations has encouraged us to study DNA methylation in a cohort of 83 patients with Müllerian aplasia (MA). Site-specific methylation analyses of H19 ICR1 by quantitative real-time polymerase chain reaction in 80 clinically well-diagnosed Finnish MA patients showed no association between hypomethylation and the MA phenotype, but studies of the H19 locus in 38 patients showed aberrant methylation in 3/16 studied sites.

Association of intramyocellular, intraperitoneal and liver fat with glucose tolerance in severely obese adolescents

OBJECTIVE

Impaired glucose tolerance (IGT) is common among obese adolescents. The aim of the present study was to investigate the association between glucose tolerance and intramyocellular, intra-abdominal and liver fat in adolescents presenting with early-onset severe obesity.

DESIGN AND METHODS

We studied 21 adolescents (mean age 13.5 years, range 11.5-15.9 years) referred to secondary care due to severe obesity (relative weight for height > +60% or body mass index > 98th percentile for age and sex, before the age of 10 years) and their eight non-obese siblings (mean age 14.4 years, range 11.8-16.7 years). All subjects underwent oral glucose tolerance tests, followed by magnetic resonance spectroscopy (MRS) to measure the intramyocellular fat content in mainly oxidative soleus and mainly glycolytic tibialis anterior muscles. MRS was also used to measure liver fat. Abdominal fat (subcutaneous, intraperitoneal and retroperitoneal) was measured using MR imaging.

RESULTS

Compared with their non-obese siblings, the obese adolescents had increased fat deposition in all anatomic locations studied. Eight obese adolescents had IGT, and they also had increased intramyocellular fat in the soleus (P=0.03) and increased intraperitoneal fat (P=0.04) compared with obese subjects with normal glucose tolerance (NGT). In contrast, no significant difference was seen between obese adolescents with NGT and IGT in liver fat (P=0.9) or intramyocellular fat in the tibialis anterior (P=0.13). In logistic regression analysis, increased soleus intramyocellular fat and intraperitoneal fat were significant predictors of IGT.

CONCLUSIONS

IGT in obese adolescents is associated with increased intramyocellular and intraperitoneal fat rather than liver fat.

Submicroscopic genomic alterations in Silver-Russell syndrome and Silver-Russell-like patients

BACKGROUND

Silver-Russell syndrome (SRS, OMIM 180860) features fetal and postnatal growth restriction and variable dysmorphisms. Genetic and epigenetic aberrations on chromosomes 7 and 11 are commonly found in SRS. However, a large fraction of SRS cases remain with unknown genetic aetiology.

METHODS

22 patients with a diagnosis of SRS (10 with H19 hypomethylation and 12 of unknown molecular aetiology) and their parents were studied with the Affymetrix 250K Sty microarray. Several analytical approaches were used to identify genomic aberrations such as copy number changes (CNCs), loss of heterozygosity (LOH) and uniparental disomy (UPD). Selected CNCs were verified with quantitative real-time PCR.

RESULTS

The largest unambiguous CNCs were found in patients with previously molecularly unexplained SRS with relatively mild phenotypes: a heterozygous deletion of chromosome 15q26.3 including the IGF1R gene (2.6 Mb), an atypical distal 22q11.2 deletion (1.1 Mb), and a pseudoautosomal region duplication (2.7 Mb) in a male patient. LOH regions of potential relevance to the SRS phenotype were also identified. Importantly, no duplications or UPD of chromosomes 7 or 11 were identified.

CONCLUSION

Unexpected submicroscopic genomic events with pathogenic potential were found in three patients with molecularly unexplained SRS that was mild. The findings emphasise that SRS is heterogeneous in genetic aetiology beyond the major groups of H19 hypomethylation and maternal UPD7 and that unbiased genome-scale screens may reveal novel genotype-phenotype correlations.

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.

Restriction Site–Specific Methylation Studies of Imprinted Genes with Quantitative Real-Time PCR

Background: Epigenetic studies, such as the measurement of DNA methylation, are important in the investigation of syndromes influenced by imprinted genes. Quick and accurate quantification of methylation at such genes can be of appreciable diagnostic aid.

Methods: We first digested genomic DNA with methylation-sensitive restriction enzymes and used DNA without digestion as a control and nonmethylated λ DNA as an internal control for digestion efficiency. We then performed quantitative real-time PCR analyses with 6 unique PCR assays to investigate 4 imprinting control regions on chromosomes 7 and 11 in individuals with uniparental disomy of chromosome 7 (UPD7) and in control individuals.

Results: Our validation of the method demonstrated both quantitative recovery and low methodologic imprecision. The imprinted loci on chromosome 7 behaved as expected in maternal UPD7 (100% methylation) and paternal UPD7 (&lt;10% methylation). In controls, the mean (SD) for percent methylation at 2 previously well-studied restriction sites were 46% (6%) for both H19 and KCNQ1OT1, a result consistent with the previously observed methylation rate of approximately 50%. The methylation percentages of all investigated imprinted loci were normally distributed, implying that the mean and SD can be used as a reference for screening methylation loss or gain.

Conclusion: The investigated loci are of particular importance for investigating the congenital Silver–Russell and Beckwith–Wiedemann syndromes; however, the method can also be applied to other imprinted regions. This method is easy to set up, has no PCR bias, requires small amounts of DNA, and can easily be applied to large patient populations for screening the loss or gain of methylation.

Insufficient growth hormone secretion is associated with metabolic syndrome after allogeneic stem cell transplantation in childhood

The aim was to evaluate whether the metabolic syndrome associates with other endocrinopathies observed after allogeneic stem cell transplantation (SCT) in childhood. Thirty-one SCT long-term survivors, transplanted for leukemia (n=26) or nonmalignant hematologic diseases (n=5) were evaluated by oral glucose tolerance test and assessment of serum lipids at a median age of 15 (range 7 to 34) years. Hyperinsulinemia, hypertriglyceridemia, and abdominal obesity were required for the diagnosis of metabolic syndrome. Growth hormone (GH) secretion was evaluated either with GH releasing hormone and arginine (n=14), clonidine (n=15), or insulin-tolerance (n=2) test. A GH peak level of <20 mU/L was considered insufficient. The thyroid and gonadal functions were assessed. Twelve patients (39%) had metabolic syndrome. Nine out of 12 (75%) patients with metabolic syndrome had insufficient GH response in provocative testing as opposed to 6/19 (31%) of those without it (P=0.02). No difference was observed in thyroid or gonadal function between patients with versus without metabolic syndrome. In conclusion, metabolic syndrome is frequently associated with insufficient GH secretion in the SCT long-term survivors. This should implicate a close follow-up of the metabolic parameters in SCT patients with either frank GH insufficiency or signs of inadequate GH response in provocative testing.

Growth and growth hormone therapy in subjects with mulibrey nanism

OBJECTIVES

Mulibrey nanism is a monogenic disorder with prenatal-onset growth restriction, mild dysmorphic features, and a strong tendency for insulin resistance but no major neurologic handicap. Growth hormone therapy has been shown to promote short-term growth in children born small for gestational age, but the experience with long-term therapy is insufficient. Growth in patients with mulibrey nanism has not been analyzed previously in detail.

METHODS

We evaluated the natural growth pattern and long-term impact of growth hormone treatment in the largest cohort of subjects with mulibrey nanism to date. The study included 72 living subjects followed up to 30 years. Thirty (18 female) were treated with recombinant human growth hormone for a median period of 5.7 years. Patients were reviewed at baseline and every 6 to 12 months during the therapy. Evaluation included assessment of height, weight, and pubertal status and laboratory analyses. Glucose metabolism was evaluated by oral glucose-tolerance test.

RESULTS

The patients were born small for gestational age with immature craniofacial features. They experienced a continuous deceleration in height (median decrement of 1.1 SDS) and weight for height (median reduction of 17%) in infancy followed by an incomplete catch-up growth lasting up to school age. The final adult height averaged 136 cm in girls and 150 cm in boys. Growth hormone treatment improved the prepubertal growth but had only little impact on adult height (+5 cm). The treated subjects showed earlier bone maturation and growth arrest but not a significant increase in insulin resistance. On the contrary, the subjects who were treated with growth hormone were slimmer and had less metabolic syndrome as young adults.

CONCLUSIONS

The patients with mulibrey nanism showed a distinct postnatal growth pattern. The growth hormone treatment was safe and induced a good short-term effect, but the impact on the adult height remained modest.

Cardiac dysfunction in children with mulibrey nanism

Mulibrey nanism is an autosomal recessive disease with severe growth failure and multiple organ involvement. Heart manifestations include constrictive pericarditis and restrictive cardiomyopathy. The purpose of this study was to evaluate left ventricular (LV) diastolic and systolic function in children with mulibrey nanism utilizing two- and three- dimensional (2-D and 3-D) echocardiography and measurement of serum levels of natriuretic peptides. Of the 30 children diagnosed with mulibrey nanism in Finland, 26 participated. The control group comprised 26 children. In 2-D echocardiography, the interventricular septum and LV posterior wall were thicker in patients. The left atrium/aorta ratio measured a median 1.8 (range, 1.4-2.5) in patients and 1.3 (range, 1.0-1.7) in controls (p < 0.001). Patients differed from controls in several indices of diastolic LV function. In 3-D echocardiography, LV end diastolic volume measured a median of 51.9 ml/m(2) (range, 33.3-73.4) in patients and 59.7 ml/m(2) (range, 37.6-87.6) in controls (p = 0.040), and serum levels of N-terminal proatriopeptide and N-terminal pro-brain natriuretic peptide measured, respectively, a median of 0.54 nmol/L (range, 0.04-4.7) and 289 ng/L (range, 18-9170) in patients and 0.28 nmol/L (range, 0.09-0.72; p < 0.001) and 54 ng/L (range, 26-139; p < 0.001) in controls. They correlated with several indices of diastolic LV function. In a significant proportion of children with mulibrey nanism, myocardial function is impaired. Significant correlations appeared between indices of LV function, size of the left atrium, and levels of natriuretic peptides, showing that measurement of serum levels of natriuretic peptides is a useful follow-up method despite its dependence on loading conditions.

Absence of a paternally inherited FOXP2 gene in developmental verbal dyspraxia

Mutations in FOXP2 cause developmental verbal dyspraxia (DVD), but only a few cases have been described. We characterize 13 patients with DVD--5 with hemizygous paternal deletions spanning the FOXP2 gene, 1 with a translocation interrupting FOXP2, and the remaining 7 with maternal uniparental disomy of chromosome 7 (UPD7), who were also given a diagnosis of Silver-Russell Syndrome (SRS). Of these individuals with DVD, all 12 for whom parental DNA was available showed absence of a paternal copy of FOXP2. Five other individuals with deletions of paternally inherited FOXP2 but with incomplete clinical information or phenotypes too complex to properly assess are also described. Four of the patients with DVD also meet criteria for autism spectrum disorder. Individuals with paternal UPD7 or with partial maternal UPD7 or deletion starting downstream of FOXP2 do not have DVD. Using quantitative real-time polymerase chain reaction, we show the maternally inherited FOXP2 to be comparatively underexpressed. Our results indicate that absence of paternal FOXP2 is the cause of DVD in patients with SRS with maternal UPD7. The data also point to a role for differential parent-of-origin expression of FOXP2 in human speech development.

A two-base deletion -439delGC in the melanocortin-4 receptor promoter associated with early-onset obesity

BACKGROUND/AIMS

Mutations in melanocortin-4 receptor (MC4R) are the most common genetic cause of human obesity. Mutations in MC4R promoter could also underlie obesity, but have so far not been reported. Transcription factor nescient helix-loop-helix 2 (Nhlh2) is a novel obesity candidate gene. We searched for mutations in MC4R promoter and Nhlh2 gene in 152 children with severe early-onset obesity. Lean subjects (n = 447) served as controls.

METHODS

MC4R promoter and Nhlh2 gene were investigated by sequencing. Gel shifts and reporter gene assays were used to investigate a deletion in MC4R promoter. Mutation carriers were carefully characterised. Weight charts from index patients and relatives were analysed.

RESULTS

We identified a deletion, -439delGC, in MC4R promoter in 2 severely obese, unrelated children and their family members, but not in controls. Index patients and mutation-carrying relatives were affected by early-onset obesity, while non-carriers had normal childhood weight development. The deletion is located at a potential Nhlh2-binding site and gel shift assays showed that Nhlh2 binds to this site. No significant differences in mutant compared to wild-type MC4R promoter activities were detected. No mutations were identified in Nhlh2 gene.

CONCLUSION

We report an MC4R promoter mutation, -439delGC, associated with early-onset obesity and show that transcription factor Nhlh2 recognises this site in vitro. Nhlh2 mutations unlikely underlie severe human obesity.

Risk factors for reduced areal bone mineral density in young adults with stem cell transplantation in childhood

Slightly, but significantly, reduced bone mineral density (BMD) has been detected as a late effect after stem cell transplantation (SCT) performed in childhood. The aim of the study was to evaluate the risk factors of reduced BMD after SCT in childhood. We evaluated areal BMD of 16 young adults (six males, 10 females), aged 21 yr (range 15-34) by dual-energy X-ray absorptiometry at the lumbar spine, at the femoral neck, in the total hip, and in the total body. Bone turnover rate was evaluated by markers of bone formation and resorption. Six of the 16 patients had reduced BMD with a Z-score of < or = -1 at least at one measurement site. Factors associated with reduced BMD were prepubertal status at transplant (p = 0.03), delayed pubertal growth (p = 0.03), pubertal onset gonadal hormone insufficiency (p = 0.02), and female sex (p = 0.02). Surprisingly, height in SDs and lumbar spine BMD correlated negatively (p = 0.008) in those with reduced bone mass, indicating that low areal density could not be due the small size of the vertebrae. Bone turnover markers were similar for those with normal and reduced BMD. In conclusion, 38% of the SCT long-term survivors had reduced areal BMD. Prepubertal status at transplant with pubertal onset gonadal hormone insufficiency and female sex predisposed to reduced bone mass after SCT performed in childhood.

Insulin resistance syndrome in subjects with mutated RING finger protein TRIM37

We evaluated the glucose and lipid metabolism in 65 patients (aged 1.1-55 years) with mulibrey (muscle-liver-brain-eye) nanism (MUL), which is a monogenic disorder with prenatal-onset growth failure and typical clinical characteristics. MUL is caused by mutations in the TRIM37 gene, encoding a peroxisomal protein (TRIM37) with E3 ubiquitin-ligase activity. The subjects underwent clinical evaluation, abdominal ultrasonography, and laboratory measurements, including a 3-h oral glucose tolerance test. The results showed a dramatic change in glucose and lipid metabolism with age in MUL subjects. While the children had low fasting glucose and insulin levels, 90% of the adults had high fasting and postload insulin values (up to 1,450 mU/l). A 10-fold decrease in the fasting glucose-to-insulin ratio and a 4-fold decrease in whole-body insulin sensitivity index were observed. Insulin resistance, fatty liver, high serum leptin, hypertension, and acantosis nigricans were already evident in many slim prepubertal children. Half of the adults had type 2 diabetes, and an additional 42% showed impaired glucose tolerance. Seventy percent fulfilled the National Cholesterol Education Program criteria for metabolic syndrome. The peroxisomal targeting and the functional link of TRIM37 to the ubiquitin-proteosome pathway may provide novel clues to the development of metabolic syndrome.

TRIM37 defective in mulibrey nanism is a novel RING finger ubiquitin E3 ligase

Mulibrey nanism is an autosomal recessive prenatal-onset growth disorder characterized by dysmorphic features, cardiomyopathy, and hepatomegaly. Mutations in TRIM37 encoding a tripartite motif (TRIM, RING-B-box-coiled-coil)-family protein underlie mulibrey nanism. We investigated the ubiquitin ligase activity predicted for the RING domain of TRIM37 by analyzing its autoubiquitination. Full-length TRIM37 and its TRIM domain were highly polyubiquitinated when co-expressed with ubiquitin. Polyubiquitination was decreased in a mutant protein with disrupted RING domain (Cys35Ser;Cys36Ser) and in the Leu76Pro mutant protein, a disease-associated missense mutation affecting the TRIM domain of TRIM37. Bacterially produced GST-TRIM domain fusion protein, but not its Cys35Ser;Cys36Ser or Leu76Pro mutants, were polyubiquitinated in cell-free conditions, implying RING-dependent modification. Ubiquitin was also identified as an interaction partner for TRIM37 in a yeast two-hybrid screen. Ectopically expressed TRIM37 rapidly formed aggregates that were ubiquitin-, proteasome subunit-, and chaperone-positive in immunofluorescence analysis, defining them as aggresomes. The Cys35Ser;Cys36Ser mutant and the Leu76Pro and Gly322Val patient mutant proteins were markedly less prone to aggregation, implying that aggresomal targeting reflects a physiological function of TRIM37. These findings suggest that TRIM37 acts as a TRIM domain-dependent E3 ubiquitin ligase and imply defective ubiquitin-dependent degradation of an as-yet-unidentified target protein in the pathogenesis of mulibrey nanism.

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.

Cardiac Involvement in Mulibrey Nanism: Characterization with Magnetic Resonance Imaging

Mulibrey nanism (MUL) is an autosomal recessive disorder that is enriched in the Finnish population. Variable degrees of pericardial and myocardial involvement can lead to heart failure and premature death. The purpose of this study was using magnetic resonance imaging (MRI) to assess structural and functional abnormalities of the MUL cardiopathy in all four cardiac chambers as well as in the pericardium. Thirty-one patients with MUL (mean age 27, range 15-50 years) and 16 controls (mean age 31, range 19-45 years) were examined with a Siemens Vision 1.5-T imager. Ten patients had undergone pericardiectomies to relieve symptoms of constrictive pericarditis. In surgery performed 0.5-25 years before MRI, the removed pericardium was found to be thickened and consisting of scarlike fibrosis. Turbo spin echo images were obtained for assessment of pericardial thickness, and breath hold left ventricular (LV) short axis and four-chamber cine images were obtained for the volumetric data. In MRI, pericardial thickness was normal (under 3.4 mm) in all patients with MUL. In the 10 pericardiectomized patients, the remnants of the pericardium were of normal thickness as well. The LV septum (p = 0.01) and posterior wall (p<0.001) were hypertrophied and end-diastolic volumes of both ventricles (p<0.05) were reduced in all patients. The LV systolic function was preserved. The volume chance during the first third of diastole (p = 0.030), the absolute peak filling rate (p = 0.047), and the time to peak rate of LV diastolic filling (p = 0.030) indicated restrictive LV diastolic filling. The right ventricular ejection fraction and contraction of both atria were reduced.

Novel mutations in theTRIM37gene in Mulibrey Nanism

Mulibrey nanism is an autosomal recessive prenatal-onset growth disorder of unknown pathogenesis. The main clinical features are pre- and postnatal growth failure, characteristic dysmorphic craniofacial features, heart disease, and hepatomegaly. Five truncating mutations in the TRIM37 gene have previously been reported in Mulibrey nanism patients. The TRIM37 protein encodes a novel protein of unknown function. It contains a tripartite motif (TRIM, also denoted the RING-B-box-Coiled-coil or RBCC domain) and a TRAF (tumor necrosis factor-receptor associated factor) domain. TRIM37 localizes to peroxisomes classifying Mulibrey nanism as a peroxisomal disorder. Here we have characterized the genomic structure of the TRIM37 gene, which has 24 exons spanning approximately 109 kb of genomic DNA. Further, we report six novel disease-associated mutations, five of which predict a truncated protein: c.745C>T (p.Gln249X), c.1411C>T (p.Arg471X), c.2056C>T (p.Arg686X), and an 8.6 kb genomic deletion (c.1314+507_1668-207del resulting in p.Arg439fsX4). The sixth mutation (c.965G>T) is the first missense mutation (p.Gly322Val) associated with Mulibrey nanism. It affects the TRAF domain of TRIM37 and results in altered subcellular localization of the mutant TRIM37 protein, further suggesting that it is pathogenic.

Mulibrey nanism: clinical features and diagnostic criteria

Mulibrey nanism (MUL) is an autosomal recessive disease caused by mutations in the TRIM37 gene encoding the peroxisomal TRIM37 protein of unknown function. In this work, we analysed the clinical characteristics of 85 Finnish patients with MUL, most of whom were homozygous for the Finn major mutation of TRIM37. The patients' hospital records from birth to the time of the diagnosis at age 0.02-52 years (median 2.1 years) were retrospectively analysed. All except four of the patients (95%) had a prenatal onset growth failure without postnatal catch up growth. The mean length standard deviation score (SDS) was -3.1 and -4.0 at birth and at diagnosis, respectively. In infancy, feeding difficulties, and respiratory tract infections were the most common problems. Congestive heart failure and pericardial constriction were diagnosed during infancy in 12% and 6% of the patients, respectively. At the time of the diagnosis, characteristic craniofacial features of scaphocephaly, facial triangularity, high and broad forehead, and low nasal bridge were evident in over 90% of the patients. In addition, practically all patients were gracile and had thin extremities. Other findings included a peculiar high-pitched voice (96%), yellowish dots in ocular fundi (79%), cutaneous naevi flammei (65%), hepatomegaly (45%), and fibrous dysplasia of long bones (25%). Mild muscular hypotonicity (68%) was the only neurological abnormality. The clinical features of the Finnish patients with MUL formed a distinct entity. The most consistent findings were growth failure and characteristic craniofacial features. However, organ manifestations varied considerably in early childhood. Based on these findings, we propose new diagnostic criteria for MUL.

Identification and characterization of melanocortin-4 receptor gene mutations in morbidly obese finnish children and adults

Two Finnish cohorts, comprising 56 children with severe early-onset obesity (relative weight for height greater than or equal to +70% before age 10) and 252 morbidly obese adults (body mass index, > or = 40 kg/m(2)), were screened for melanocortin-4 receptor (MC4R) mutations. We identified a pathogenic mutation (S127L) in one child, causing severe early-onset obesity. We describe the phenotype of this particular mutation for the first time. We also identified a novel (I226T) polymorphism in the coding and two new variations (-439delGC and 1059C>T) outside the coding region of the MC4R gene. Three previously described polymorphisms (V103I, T112M, and I125L) were identified. In vitro functional studies of variants T112M, S127L, and I226T supported a pathogenic role of the S127L mutation, because signaling properties of the receptor in response to the MC4R agonists alpha-MSH, beta-MSH, and gamma(1)-MSH were impaired. The S127L mutation did not affect receptor inhibition by the antagonist agouti-related protein. Localization of the three variant receptors was similar to that of wild type. In conclusion, a pathogenic MC4R mutation was found among subjects with severe early-onset obesity but not among morbidly obese adults. Impaired function of the S127L receptor was due to reduced activation, not a defect of protein transport to the cell membrane.

Mulibrey heart disease: clinical manifestations, long-term course, and results of pericardiectomy in a series of 49 patients born before 1985

BACKGROUND

Mulibrey nanism is a rare inherited disease characterized by growth failure and multiorgan manifestations, including constrictive pericarditis. Its long-term course, the results of pericardiectomy, and the details of myocardial involvement have not been reported previously.

METHODS AND RESULTS

We studied 49 patients (26 men) born before 1985 and followed for up to 25 years. By 1999, 25 patients (51%) had developed congestive heart failure (CHF), 19 (39%) had undergone pericardiectomy for constrictive pericarditis, 10 (22%) had died of cardiac causes, and 5 (10%) had died of noncardiac causes. Of the 19 pericardiectomized patients, 12 derived lasting clinical benefit, whereas 1 patient suffered an early noncardiac death and 6 died later of unrelieved or recurrent CHF. At echocardiography in 34 living patients, left ventricular mass adjusted for body height and weight averaged (+/-SEM) 149+/-5 g in 21 unoperated patients, 144+/-8 g in 13 pericardiectomized patients, and 104+/-7 g in 16 healthy persons matched for age and sex (P=0.000). Autopsies of 11 patients showed fibrotic thickening of the pericardial leaves with myocardial hypertrophy and variable but mostly mild myocardial fibrosis. Endocardial thickening was seen in 3 patients.

CONCLUSIONS

Constrictive pericarditis, myocardial hypertrophy, and variable myocardial fibrosis constitute the main elements of Mulibrey heart disease. At least one half of patients ultimately develop CHF. Pericardiectomy generally provides clinical benefit, but in approximately one third of patients, CHF may recur because of coexisting myocardial involvement.

The TRIM37 gene encodes a peroxisomal RING-B-box-coiled-coil protein: classification of mulibrey nanism as a new peroxisomal disorder

Mulibrey nanism is a rare growth disorder of prenatal onset caused by mutations in the TRIM37 gene, which encodes a RING-B-box-coiled-coil protein. The pathogenetic mechanisms of mulibrey nanism are unknown. We have used transiently transfected cells and antibodies raised against the predicted TRIM37 protein to characterize the TRIM37 gene product and to determine its intracellular localization. We show that the human TRIM37 cDNA encodes a peroxisomal protein with an apparent molecular weight of 130 kD. Peroxisomal localization is compromised in mutant protein representing the major Finnish TRIM37 mutation but is retained in the protein representing the minor Finnish mutation. Colocalization of endogenous TRIM37 with peroxisomal markers was observed by double immunofluorescence staining in HepG2 and human intestinal smooth muscle cell lines. In human tissue sections, TRIM37 shows a granular cytoplasmic pattern. Endogenous TRIM37 is not imported into peroxisomes in peroxin 1 (PEX1(-/-)) and peroxin 5 (PEX5(-/-)) mutant fibroblasts but is imported normally in peroxin 7 (PEX7(-/-)) deficient fibroblasts, giving further evidence for a peroxisomal localization of TRIM37. Fibroblasts derived from patients with mulibrey nanism lack C-terminal TRIM37 immunoreactivity but stain normally for both peroxisomal matrix and membrane markers, suggesting apparently normal peroxisome biogenesis in patient fibroblasts. Taken together, this molecular evidence unequivocally indicates that TRIM37 is located in the peroxisomes, and Mulibrey nanism thus can be classified as a new peroxisomal disorder.

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.

Maternal and Paternal Chromosomes 7 Show Differential Methylation of Many Genes in Lymphoblast DNA

Genomic imprinting, the differential expression of paternal and maternal alleles, involves many chromosomal regions and plays a role in development and growth. Differential methylation of maternal and paternal alleles is a hallmark of imprinted genes, and thus methylation assays are widely used to support the identification of novel imprinted genes. Either blood or lymphoblast DNAs are most often used in these assays, even though methylation levels may change in cell culture. We undertook a systematic survey of parent-of-origin-specific methylation of chromosome 7 genes and ESTs by comparing DNA samples from cases of maternal and paternal uniparental disomy for chromosome 7 using DNA from fresh blood and lymphoblast cell lines. Our results revealed that up to 41% of genes and ESTs show parent-of-origin-specific methylation differences in lymphoblast DNA after only a short time in culture, whereas methylation differences were not seen in blood DNA. The methylation changes occurred most commonly on paternal chromosome 7, whereas alterations on maternal chromosome 7 were more infrequent and weaker. These findings indicate that methylation patterns may change significantly during cell culture in a parent-of-origin-dependent manner and suggest that methylation is maintained differently on maternal and paternal chromosomes 7.

A narrow segment of maternal uniparental disomy of chromosome 7q31-qter in Silver-Russell syndrome delimits a candidate gene region

Maternal uniparental disomy of chromosome 7 (matUPD7), the inheritance of both chromosomes from only the mother, is observed in approximately 10% of patients with Silver-Russell syndrome (SRS). It has been suggested that at least one imprinted gene that regulates growth and development resides on human chromosome 7. To date, three imprinted genes-PEG1/MEST, gamma2-COP, and GRB10-have been identified on chromosome 7, but their role in the etiology of SRS remains uncertain. In a systematic screening with microsatellite markers, for matUPD7 cases among patients with SRS, we identified a patient who had a small segment of matUPD7 and biparental inheritance of the remainder of chromosome 7. Such a pattern may be explained by somatic recombination in the zygote. The matUPD7 segment at 7q31-qter extends for 35 Mb and includes the imprinted gene cluster of PEG1/MEST and gamma2-COP at 7q32. GRB10 at 7p11.2-p12 is located within a region of biparental inheritance. Although partial UPD has previously been reported for chromosomes 6, 11, 14, and 15, this is the first report of a patient with SRS who has segmental matUPD7. Our findings delimit a candidate imprinted region sufficient to cause SRS.

Impaired glucose tolerance and dyslipidaemia as late effects after bone-marrow transplantation in childhood

BACKGROUND

This follow-up study aimed to assess the frequency of late effects on glucose and lipid metabolism after bone-marrow transplantation in childhood.

METHODS

23 long-term survivors (median age 20 years) were studied 3-18 years after bone-marrow transplantation and compared with 23 healthy controls matched for age and sex and with 13 patients in remission from leukaemia.

FINDINGS

12 (52%) of the 23 bone-marrow transplantation patients had insulin resistance, including impaired glucose tolerance in six and type 2 diabetes in four. The core signs of the metabolic syndrome (hyperinsulinaemia and hypertriglyceridaemia combined), were found in nine (39%) of the bone-marrow transplantation patients compared with one (8%) of the 13 leukaemia patients and none of the healthy controls (p=0.0015). The frequency of insulin resistance increased with the time since bone-marrow transplantation. Abdominal obesity, but not overweight, was common among the patients with insulin resistance.

INTERPRETATION

Long-term survivors of bone-marrow transplantation are at substantial risk of insulin resistance, impaired glucose tolerance, and type 2 diabetes even at normal weight and young age. They also develop typical signs of the metabolic syndrome. We advocate measurement of serum lipids, fasting blood glucose, and serum insulin for the follow-up of all patients who undergo transplants in childhood, to be continued regularly and possibly life-long.

Gene encoding a new RING-B-box-Coiled-coil protein is mutated in mulibrey nanism

Mulibrey nanism (for muscle-liver-brain-eye nanism, MUL; MIM 253250) is an autosomal recessive disorder that involves several tissues of mesodermal origin, implying a defect in a highly pleiotropic gene. Characteristic features include severe growth failure of prenatal onset and constrictive pericardium with consequent hepatomegaly. In addition, muscle hypotonia, J-shaped sella turcica, yellowish dots in the ocular fundi, typical dysmorphic features and hypoplasia of various endocrine glands causing hormonal deficiency are common. About 4% of MUL patients develop Wilms' tumour. MUL is enriched in the Finnish population, but is rare elsewhere. We previously assigned MUL to chromosome 17q22-q23 and constructed a physical contig over the critical MUL region. The region has now been further refined by haplotype analysis and new positional candidate genes have been localized. We identified a gene with four independent MUL-associated mutations that all cause a frameshift and predict a truncated protein. MUL is ubiquitously expressed and encodes a new member of the RING-B-box-Coiled-coil (RBCC) family of zinc-finger proteins, whose members are involved in diverse cellular functions such as developmental patterning and oncogenesis.

High frequency of mutations in MODY and mitochondrial genes in Scandinavian patients with familial early-onset diabetes

AIMS/HYPOTHESIS

To investigate the contribution of mutations in maturity-onset diabetes of the young (MODY) and mitochondrial genes to early-onset diabetes with a strong family history of diabetes in a cohort with a high prevalence of Type I (insulin-dependent) diabetes mellitus.

METHODS

Screening for sequence variants in the hepatocyte nuclear factor (HNF)-4alpha (MODY1), glucokinase (MODY2), HNF-1alpha (MODY3) genes and mitochondrial DNA was carried out in 115 Finnish and Swedish patients with early-onset ( </= 40 years) diabetes using the single strand conformation polymorphism (SSCP) technique and direct sequencing. Allele frequencies were compared with 118 patients with onset of diabetes Type II (non-insulin-dependent) diabetes mellitus after the age of 40 and 92 non-diabetic control subjects without a family history of diabetes.

RESULTS

In total 52 sequence variants were found in the HNF-1alpha, HNF-4alpha and glucokinase genes, 12 of which were considered as MODY mutations. Three families had the A3243G mutation in the mitochondrial tRNA(Leu) gene, which resulted in an overall prevalence of these mutations of 13 %.

CONCLUSION/INTERPRETATION

Among 115 Scandinavian families, mutations in the HNF-1alpha gene represented the most common cause of familial early-onset ( </= 40 years) diabetes: MODY3 (5.2 %) more than MODY2 (3.5 %) more than MIDD (2.6 %) more than MODY1 (1.7 %).