Congenital imprinting disorders: EUCID.net - a network to decipher their aetiology and to improve the diagnostic and clinical care.

Imprinting disorders (IDs) are a group of eight rare but probably underdiagnosed congenital diseases affecting growth, development and metabolism. They are caused by similar molecular changes affecting regulation, dosage or the genomic sequence of imprinted genes. Each ID is characterised by specific clinical features, and, as each appeared to be associated with specific imprinting defects, they have been widely regarded as separate entities. However, they share clinical characteristics and can show overlapping molecular alterations. Nevertheless, IDs are usually studied separately despite their common underlying (epi)genetic aetiologies, and their basic pathogenesis and long-term clinical consequences remain largely unknown. Efforts to elucidate the aetiology of IDs are currently fragmented across Europe, and standardisation of diagnostic and clinical management is lacking. The new consortium EUCID.net (European network of congenital imprinting disorders) now aims to promote better clinical care and scientific investigation of imprinting disorders by establishing a concerted multidisciplinary alliance of clinicians, researchers, patients and families. By encompassing all IDs and establishing a wide ranging and collaborative network, EUCID.net brings together a wide variety of expertise and interests to engender new collaborations and initiatives

Growth and disease burden in children with hypophosphatasia

Hypophosphatasia, an inborn error of metabolism characterized by impaired bone mineralization, can affect growth. This study evaluated relationships between anthropometric parameters (height, weight, and body mass index) and clinical manifestations of hypophosphatasia in children. Design: Data from children (aged < third percentile) and those with normal stature. Methods: Anthropometric parameters were evaluated by age group (< third percentile) and those with normal stature. Results: This analysis included 215 children (54.4% girls). Short stature presented in 16.1% of children aged<2 years and 20.4% of those aged≥2 years at assessment. Among those with available data (n = 62), height was below the target height (mean: −0.66 standard deviations). Substantial worsening of growth (mean delta height z score: −1.45; delta weight z score: −0.68) occurred before 2 years of age, while in those aged≥2 years, anthropometric trajectories were maintained (delta height z score: 0.08; delta weight z score: 0.13). Broad-ranging hypophosphatasia manifestations (beyond dental) were observed in most children. Conclusions: Short stature was not a consistent characteristic of children with hypophosphatasia, but growth impairment was observed in those aged<2 years, indicating that hypophosphatasia might affect growth plate activity during infancy. In addition, a broad range of clinical manifestations occurred in those above and below the third percentile for height, suggesting that height alone may not accurately reflect hypophosphatasia disease burden and that weight is less affected than longitudinal growt

Burosumab for X-linked hypophosphatemia in children and adolescents: opinion based on early experience in seven European countries

Given the relatively recent introduction of burosumab in the management of X-linked hypophosphatemia (XLH), there is limited real-world data to guide its use in clinical practice. As a group of European physicians experienced with burosumab treatment in clinical practice, we convened with the objective of sharing these practice-based insights on the use of burosumab in children and adolescents with XLH. We attended two virtual meetings, then discussed key questions via Within3, a virtual online platform. Points of discussion related to patient selection criteria, burosumab starting dose, dose titration and treatment monitoring. Our discussions revealed that criteria for selecting children with XLH varied across Europe from all children above 1 year to only children with overt rickets despite conventional treatment being eligible. We initiated burosumab dosing according to guidance in the Summary of Product Characteristics, an international consensus statement from 2019 and local country guidelines. Dose titration was primarily guided by serum phosphate levels, with some centers also using the ratio of tubular maximum reabsorption of phosphate to glomerular filtration rate (TmP/GFR). We monitored response to burosumab treatment clinically (growth, deformities, bone pain and physical functioning), radiologically (rickets and deformities) and biochemically (serum phosphate, alkaline phosphatase, 1,25-dihydroxyvitamin D, 25-hydroxyvitamin D, urine calcium-creatinine ratio and TmP/GFR). Key suggestions made by our group were initiation of burosumab treatment in children as early as possible, from the age of 1 year, particularly in those with profound rickets, and a need for clinical studies on continuation of burosumab throughout adolescence and into adulthoo

Congenital imprinting disorders: EUCID.net - a network to decipher their aetiology and to improve the diagnostic and clinical care

Imprinting disorders (IDs) are a group of eight rare but probably underdiagnosed congenital diseases affecting growth, development and metabolism. They are caused by similar molecular changes affecting regulation, dosage or the genomic sequence of imprinted genes. Each ID is characterised by specific clinical features, and, as each appeared to be associated with specific imprinting defects, they have been widely regarded as separate entities. However, they share clinical characteristics and can show overlapping molecular alterations. Nevertheless, IDs are usually studied separately despite their common underlying (epi) genetic aetiologies, and their basic pathogenesis and long-term clinical consequences remain largely unknown. Efforts to elucidate the aetiology of IDs are currently fragmented across Europe, and standardisation of diagnostic and clinical management is lacking. The new consortium EUCID.net (European network of congenital imprinting disorders) now aims to promote better clinical care and scientific investigation of imprinting disorders by establishing a concerted multidisciplinary alliance of clinicians, researchers, patients and families. By encompassing all IDs and establishing a wide ranging and collaborative network, EUCID.net brings together a wide variety of expertise and interests to engender new collaborations and initiatives

Imprinting disorders: a group of congenital disorders with overlapping patterns of molecular changes affecting imprinted loci

Congenital imprinting disorders (IDs) are characterised by molecular changes affecting imprinted chromosomal regions and genes, i.e. genes that are expressed in a parent-of-origin specific manner. Recent years have seen a great expansion in the range of alterations in regulation, dosage or DNA sequence shown to disturb imprinted gene expression, and the correspondingly broad range of resultant clinical syndromes. At the same time, however, it has become clear that this diversity of IDs has common underlying principles, not only in shared molecular mechanisms, but also in interrelated clinical impacts upon growth, development and metabolism. Thus, detailed and systematic analysis of IDs can not only identify unifying principles of molecular epigenetics in health and disease, but also support personalisation of diagnosis and management for individual patients and families

Genome-wide DNA methylation analysis of pseudohypoparathyroidism patients with GNAS imprinting defects

Background: Pseudohypoparathyroidism (PHP) is caused by (epi) genetic defects in the imprinted GNAS cluster. Current classification of PHP patients is hampered by clinical and molecular diagnostic overlaps. The European Consortium for the study of PHP designed a genome-wide methylation study to improve molecular diagnosis. Methods: The Human Methylation 450K BeadChip was used to analyze genome-wide methylation in 24 PHP patients with parathyroid hormone resistance and 20 age- and gender-matched controls. Patients were previously diagnosed with GNAS-specific differentially methylated regions (DMRs) and include 6 patients with known STX16 deletion (PHP Delta stx16) and 18 without deletion (PHPneg). Results: The array demonstrated that PHP patients do not show DNA methylation differences at the whole-genome level. Unsupervised clustering of GNAS-specific DMRs divides PHP Delta stx16 versus PHPneg patients. Interestingly, in contrast to the notion that all PHP patients share methylation defects in the A/B DMR while only PHP Delta stx16 patients have normal NESP, GNAS-AS1 and XL methylation, we found a novel DMR (named GNAS-AS2) in the GNAS-AS1 region that is significantly different in both PHP Delta stx16 and PHPneg, as validated by Sequenom EpiTYPER in a larger PHP cohort. The analysis of 58 DMRs revealed that 8/18 PHPneg and 1/6 PHP Delta stx16 patients have multi-locus methylation defects. Validation was performed for FANCC and SVOPL DMRs. Conclusions: This is the first genome-wide methylation study for PHP patients that confirmed that GNAS is the most significant DMR, and the presence of STX16 deletion divides PHP patients in two groups. Moreover, a novel GNAS-AS2 DMR affects all PHP patients, and PHP patients seem sensitive to multi-locus methylation defects

Combined gait analysis and radiologic examination in children with X-linked hypophosphatemia

Autre financement : Kyowa Kirin PharmaBackground: X-linked hypophosphataemia causes bone deformities and gait abnormalities that tend to worsen with age in the absence of appropriate treatment. However, doctors do not currently use quantitative tools to characterize these symptoms and their possible interactions. Methods: Radiographs and 3D gait data from 43 non-surgical growing children with X-linked hypophosphataemia were acquired prospectively. Data from age-matched typically developing children were used to form the reference group. Subgroups based on radiological parameters were compared with each other and with the reference population. Linear correlations between radiographic parameters and gait variables were examined. Finding: X-linked hypophosphatemic patients differed from the control group in pelvic tilt, ankle plantarflexion, knee flexion moment and power. High correlations with tibiofemoral angle were found for trunk lean, knee and hip adduction, and knee abduction moment. The Gait Deviation Index was below 80 for 88% of the patients with a high tibiofemoral angle (varus). Compared to other subgroups, varus patients had augmented trunk lean (+3°) and knee adduction (+10°) and decreased hip adduction (-5°) and ankle plantarflexion (-6°). Femoral torsion was associated with alterations in rotation at the knee, and hip. Interpretation: Gait abnormalities induced in X-linked hypophosphataemia have been described in a large cohort of children. Links between gait alterations and lower limb deformities were found, with varus deformities standing out. Since bony deformities appear when X-linked hypophosphatemic children start walking and have been found to alter gait patterns, we suggest that combining radiology with gait analysis may improve the clinical management of X-linked hypophosphataemia