GNAQ/GNA11 Mosaicism Is Associated with Abnormal Serum Calcium Indices and Microvascular Neurocalcification.

Mosaic mutations in genes GNAQ or GNA11 lead to a spectrum of diseases including Sturge-Weber syndrome and phakomatosis pigmentovascularis with dermal melanocytosis. The pathognomonic finding of localized "tramlining" on plain skull radiography, representing medium-sized neurovascular calcification and associated with postnatal neurological deterioration, led us to study calcium metabolism in a cohort of 42 children. In this study, we find that 74% of patients had at least one abnormal measurement of calcium metabolism, the commonest being moderately low serum ionized calcium (41%) or high parathyroid hormone (17%). Lower levels of ionized calcium even within the normal range were significantly associated with seizures, and with specific antiepileptics despite normal vitamin D levels. Successive measurements documented substantial intrapersonal fluctuation in indices over time, and DEXA scans were normal in patients with hypocalcemia. Neurohistology from epilepsy surgery in five patients revealed not only intravascular, but perivascular and intraparenchymal mineral deposition and intraparenchymal microvascular disease in addition to previously reported findings. Neuroradiology review clearly demonstrated progressive calcium deposition in individuals over time. These findings and those of the adjoining paper suggest that calcium deposition in the brain of patients with GNAQ/GNA11 mosaicism may not be a nonspecific sign of damage as was previously thought, but may instead reflect the central postnatal pathological process in this disease spectrum.

Burosumab in management of X-linked hypophosphataemia: a retrospective cohort study of growth and serum phosphate levels.

BACKGROUND: Burosumab, an antifibroblast growth factor 23 monoclonal antibody, improves rickets severity, symptoms and growth in children with X-linked hypophosphataemia (XLH) followed up to 64 weeks in clinical trials. International dosing guidance recommends targeting normal serum phosphate concentration; however, some children may not achieve this despite maximal dosing. This study compares clinical outcomes in children with XLH on long-term burosumab treatment who achieved normal phosphate versus those who did not. METHODS: Single-centre retrospective review of a large paediatric cohort with XLH treated with burosumab. We evaluated growth and biochemical markers of bone health in those who did compared with those who did not achieve normal plasma phosphate concentration. RESULTS: Fifty-five children with XLH with median age of 11.7 (IQR 6.8-15.5) years were included. 27 (49%) had low plasma phosphate concentration, and 27 (49%) had normal phosphate after a median burosumab treatment duration of 3.3 (IQR 2.6-3.7) years. 1 (2%) did not have a recent phosphate level recorded. No difference in growth was found between normal and abnormal phosphate groups (p=0.9). CONCLUSIONS: Young children with XLH experience sustained growth on long-term burosumab treatment, although without normal plasma phosphate concentration in many. Consideration should be made to changing burosumab dosing recommendations to target normalisation of alkaline phosphatase, as opposed to plasma phosphate concentration.

Non-collagen pathogenic variants resulting in the osteogenesis imperfecta phenotype in children: a single-country observational cohort study.

BACKGROUND/OBJECTIVES: In England, children (0-18 years) with severe, complex and atypical osteogenesis imperfecta (OI) are managed by four centres (Birmingham, Bristol, London, Sheffield) in a 'Highly Specialised Service' (HSS OI); affected children with a genetic origin for their disease that is not in COL1A1 or COL1A2 form the majority of the 'atypical' group, which has set criteria for entry into the service. We have used the data from the service to assess the range and frequency of non-collagen pathogenic variants resulting in OI in a single country. METHODS: Children with atypical OI were identified through the HSS OI service database. All genetic testing for children with OI in the service were undertaken at the Sheffield Diagnostic Genetics Service. Variant data were extracted and matched to individual patients. This study was done as part of a service evaluation project registered with the Sheffield Children's Hospital Clinical Governance Department. RESULTS: One hundred of 337 children in the HSS met the 'atypical' criteria. Eighty have had genetic testing undertaken; 72 had genetic changes detected, 67 in 13 genes known to be causative for OI. The most frequently affected genes were IFITM5 (22), P3H1 (12), SERPINF1 (8) and BMP1 (6). CONCLUSION: Among children with more severe forms of OI (approximately one-third of all children with OI), around 20% have pathogenic variants in non-collagen genes. IFITM5 was the most commonly affected gene, followed by genes within the P3H1 complex. These data provide additional information regarding the likelihood of different genetic origins of the disease in children with OI, which may influence clinical care.

COPB2 loss of function causes a coatopathy with osteoporosis and developmental delay.

Coatomer complexes function in the sorting and trafficking of proteins between subcellular organelles. Pathogenic variants in coatomer subunits or associated factors have been reported in multi-systemic disorders, i.e., coatopathies, that can affect the skeletal and central nervous systems. We have identified loss-of-function variants in COPB2, a component of the coatomer complex I (COPI), in individuals presenting with osteoporosis, fractures, and developmental delay of variable severity. Electron microscopy of COPB2-deficient subjects' fibroblasts showed dilated endoplasmic reticulum (ER) with granular material, prominent rough ER, and vacuoles, consistent with an intracellular trafficking defect. We studied the effect of COPB2 deficiency on collagen trafficking because of the critical role of collagen secretion in bone biology. COPB2 siRNA-treated fibroblasts showed delayed collagen secretion with retention of type I collagen in the ER and Golgi and altered distribution of Golgi markers. copb2-null zebrafish embryos showed retention of type II collagen, disorganization of the ER and Golgi, and early larval lethality. Copb2+/- mice exhibited low bone mass, and consistent with the findings in human cells and zebrafish, studies in Copb2+/- mouse fibroblasts suggest ER stress and a Golgi defect. Interestingly, ascorbic acid treatment partially rescued the zebrafish developmental phenotype and the cellular phenotype in Copb2+/- mouse fibroblasts. This work identifies a form of coatopathy due to COPB2 haploinsufficiency, explores a potential therapeutic approach for this disorder, and highlights the role of the COPI complex as a regulator of skeletal homeostasis.

Genetic Analysis of Pediatric Primary Adrenal Insufficiency of Unknown Etiology: 25 Years' Experience in the UK.

CONTEXT: Although primary adrenal insufficiency (PAI) in children and young people is often due to congenital adrenal hyperplasia (CAH) or autoimmunity, other genetic causes occur. The relative prevalence of these conditions is poorly understood. OBJECTIVE: We investigated genetic causes of PAI in children and young people over a 25 year period. DESIGN SETTING AND PARTICIPANTS: Unpublished and published data were reviewed for 155 young people in the United Kingdom who underwent genetic analysis for PAI of unknown etiology in three major research centers between 1993 and 2018. We pre-excluded those with CAH, autoimmune, or metabolic causes. We obtained additional data from NR0B1 (DAX-1) clinical testing centers. INTERVENTION AND OUTCOME MEASUREMENTS: Genetic analysis involved a candidate gene approach (1993 onward) or next generation sequencing (NGS; targeted panels, exomes) (2013-2018). RESULTS: A genetic diagnosis was reached in 103/155 (66.5%) individuals. In 5 children the adrenal insufficiency resolved and no genetic cause was found. Pathogenic variants occurred in 11 genes: MC2R (adrenocorticotropin receptor; 30/155, 19.4%), NR0B1 (DAX-1; 7.7%), CYP11A1 (7.7%), AAAS (7.1%), NNT (6.5%), MRAP (4.5%), TXNRD2 (4.5%), STAR (3.9%), SAMD9 (3.2%), CDKN1C (1.3%), and NR5A1/steroidogenic factor-1 (SF-1; 0.6%). Additionally, 51 boys had NR0B1 variants identified through clinical testing. Although age at presentation, treatment, ancestral background, and birthweight can provide diagnostic clues, genetic testing was often needed to define the cause. CONCLUSIONS: PAI in children and young people often has a genetic basis. Establishing the specific etiology can influence management of this lifelong condition. NGS approaches improve the diagnostic yield when many potential candidate genes are involved.

Endocrine Diseases of Newborn: Epidemiology, Pathogenesis, Therapeutic Options, and Outcome "Current Insights Into Disorders of Calcium and Phosphate in the Newborn".

The physiology and regulation of bone minerals in the fetus and the newborn is significantly different from children and adults. The bone minerals calcium, phosphate and magnesium are all maintained at higher concentrations in utero to achieve adequate bone accretion. This is an integral component of normal fetal development which facilitates safe neonatal transition to post-natal life. When deciphering the cause of bone mineral disorders in newborns, the potential differential diagnosis list is broad and complex, including several extremely rare conditions. Also, significant discoveries including new embryological molecular genetic transcription factors, the role of active placental mineral transport, and hormone regulation factors have changed the understanding of calcium and phosphate homeostasis in the fetus and the newborn. This article will guide clinicians through an updated review of calcium and phosphate physiology, then review specific conditions pertinent to successful neonatal care. Furthermore, with the advancement of increasingly rapid molecular genetic testing, genomics will continue to play a greater role in this area of fetal diagnostics and prognostication.

Case report: a 10-year-old girl with primary hypoparathyroidism and systemic lupus erythematosus.

Objectives Hypoparathyroidism is a rare disease in children that occurs as a result of autoimmune destruction of the parathyroid glands, a defect in parathyroid gland development or secondary to physical parathyroid gland disturbance. Typical symptoms of hypoparathyroidism present as hypocalcaemia and hyperphosphatemia due to decreased parathyroid hormone secretion and may lead to nerve and muscles disturbances resulting in clinical manifestation of tetany, arrhythmias and epilepsy. Currently, there is no conventional hormone replacement treatment for hypoparathyroidism and therapeutic approaches include normalising mineral levels using an oral calcium supplement and active forms of vitamin D. Case presentation We present the case of a 10-year-old girl with primary hypoparathyroidism who had no prior history of autoimmune disorders, but who subsequently developed systemic lupus erythematosus.

Juvenile Paget's disease with compound heterozygous mutations in TNFRSF11B presenting with recurrent clavicular fractures and a mild skeletal phenotype.

Juvenile Paget's disease (JPD) is a rare recessively-inherited bone dysplasia. The great majority of cases described to date have had homozygous mutations in TNFRSF11B, the gene encoding osteoprotegerin. We describe a boy who presented with recurrent clavicular fractures following minor trauma (8 fractures from age 2 to 11). He was of normal height and despite mild lateral bowing of the thighs and anterior bowing of the shins he remained physically active. Abnormal modelling was noted in ribs and humeri on clavicular radiographs, and a skeletal survey at the age of 7 showed generalised diaphyseal expansion of the long bones with thickening of the periosteal and endosteal surfaces of the cortices. On biochemical evaluation, serum alkaline phosphatase was noted to be persistently elevated. The diagnosis of JPD was confirmed by the finding of compound heterozygous mutations in TNFRSF11B: a maternally-inherited A>G missense mutation at position 1 of the first amino acid codon (previously reported) and a paternally-inherited splice acceptor site mutation in intron 3 at a highly conserved position (not previously reported). Bioinformatics analysis suggested both mutations were disease-causing. Compound heterozygote mutations in TNFRSF11B causing JPD have been previously reported only once - in a boy who also had a relatively mild skeletal phenotype. The milder features may lead to delay in diagnosis and diagnostic confusion with other entities, but the extraskeletal features of JPD may nonetheless develop.

A New Multisystem Disorder Caused by the Gαs Mutation p.F376V.

CONTEXT: The α subunit of the stimulatory G protein (Gαs) links numerous receptors to adenylyl cyclase. Gαs, encoded by GNAS, is expressed predominantly from the maternal allele in certain tissues. Thus, maternal heterozygous loss-of-function mutations cause hormonal resistance, as in pseudohypoparathyroidism type Ia, whereas somatic gain-of-function mutations cause hormone-independent endocrine stimulation, as in McCune-Albright syndrome. OBJECTIVE: We report two unrelated boys presenting with a new combination of clinical findings that suggest both gain and loss of Gαs function. DESIGN AND SETTING: Clinical features were studied and sequencing of GNAS was performed. Signaling capacities of wild-type and mutant Gαs were determined in the presence of different G protein-coupled receptors (GPCRs) under basal and agonist-stimulated conditions. RESULTS: Both unrelated patients presented with unexplained hyponatremia in infancy, followed by severe early onset gonadotrophin-independent precocious puberty and skeletal abnormalities. An identical heterozygous de novo variant (c.1136T>G; p.F376V) was found on the maternal GNAS allele in both patients; this resulted in a clinical phenotype that differed from known Gαs-related diseases and suggested gain of function at the vasopressin 2 receptor (V2R) and lutropin/choriogonadotropin receptor (LHCGR), yet increased serum PTH concentrations indicative of impaired proximal tubular PTH1 receptor (PTH1R) function. In vitro studies demonstrated that Gαs-F376V enhanced ligand-independent signaling at the PTH1R, LHCGR, and V2R and, at the same time, blunted ligand-dependent responses. Structural homology modeling suggested mutation-induced modifications at the C-terminal α5 helix of Gαs that are relevant for interaction with GPCRs and signal transduction. CONCLUSIONS: The Gαs p.F376V mutation causes a previously unrecognized multisystem disorder.

Use of insulin pump therapy in children and adolescents with type 1 diabetes and its impact on metabolic control: comparison of results from three large, transatlantic paediatric registries.

AIMS/HYPOTHESIS: While the use of insulin pumps in paediatrics has expanded dramatically, there is still considerable variability among countries in the use of pump technology. The present study sought to describe differences in metabolic control and pump use in young people with type 1 diabetes using data collected in three multicentre registries. METHODS: Data for the years 2011 and 2012 from 54,410 children and adolescents were collected from the Prospective Diabetes Follow-up Registry (DPV; n = 26,198), T1D Exchange (T1DX; n = 13,755) and the National Paediatric Diabetes Audit (NPDA; n = 14,457). The modality of insulin delivery, based on age, sex and ethnic minority status, and the impact of pump use on HbA1c levels were compared. RESULTS: The overall mean HbA1c level was higher in the NPDA (8.9 ± 1.6% [74 ± 17.5 mmol/mol]) than in the DPV (8.0 ± 1.6% [64 ± 17.0 mmol/mol], p < 0.001) and T1DX (8.3 ± 1.4% [68 ± 15.4 mmol/mol], p < 0.001). Conversely, pump use was much lower in the NPDA (14%) than in the DPV (41%, p < 0.001) and T1DX (47%, p < 0.001). In a pooled analysis, pump use was associated with a lower mean HbA1c (pump: 8.0 ± 1.2% [64 ± 13.3 mmol/mol] vs injection: 8.5 ± 1.7% [69 ± 18.7 mmol/mol], p < 0.001). In all three registries, those with an ethnic minority status were less likely to be treated with a pump (p < 0.001) and boys were treated with a pump less often compared with girls (p < 0.001). CONCLUSIONS/INTERPRETATION: Despite similar clinical characteristics and proportion of minority participants, substantial differences in metabolic control exist across the three large transatlantic registries of paediatric patients with type 1 diabetes, which appears to be due in part to the frequency of insulin pump therapy.

Rates of diabetic ketoacidosis: international comparison with 49,859 pediatric patients with type 1 diabetes from England, Wales, the U.S., Austria, and Germany.

OBJECTIVE: Diabetic ketoacidosis (DKA) in children and adolescents with established type 1 diabetes is a major problem with considerable morbidity, mortality, and associated costs to patients, families, and health care systems. We analyzed data from three multinational type 1 diabetes registries/audits with similarly advanced, yet differing, health care systems with an aim to identify factors associated with DKA admissions. RESEARCH DESIGN AND METHODS: Data from 49,859 individuals <18 years with type 1 diabetes duration ≥1 year from the Prospective Diabetes Follow-up Registry (DPV) initiative (n = 22,397, Austria and Germany), the National Paediatric Diabetes Audit (NPDA; n = 16,314, England and Wales), and the T1D Exchange (T1DX; n = 11,148, U.S.) were included. DKA was defined as ≥1 hospitalization for hyperglycemia with a pH <7.3 during the prior year. Data were analyzed using multivariable logistic regression models. RESULTS: The frequency of DKA was 5.0% in DPV, 6.4% in NPDA, and 7.1% in T1DX, with differences persisting after demographic adjustment (P < 0.0001). In multivariable analyses, higher odds of DKA were found in females (odds ratio [OR] 1.23, 99% CI 1.10-1.37), ethnic minorities (OR 1.27, 99% CI 1.11-1.44), and HbA1c ≥7.5% (≥58 mmol/mol) (OR 2.54, 99% CI 2.09-3.09 for HbA1c from 7.5 to <9% [58 to <75 mmol/mol] and OR 8.74, 99% CI 7.18-10.63 for HbA1c ≥9.0% [≥75 mmol/mol]). CONCLUSIONS: These multinational data demonstrate high rates of DKA in childhood type 1 diabetes across three registries/audits and five nations. Females, ethnic minorities, and HbA1c above target were all associated with an increased risk of DKA. Targeted DKA prevention programs could result in substantial health care cost reduction and reduced patient morbidity and mortality.

Voyages of Discovery.

The metabolism of calcium and bone is controlled by five principal hormones: parathyroid hormone, 1,25-dihydroxyvitamin D, calcitonin, parathyroid hormone-related peptide and fibroblast growth factor 23, some of which have been known for several decades and some of which have only more recently been identified. The stories of the discovery of these hormones have constituted a series of complex journeys that have been undertaken over the past century or so, none of which has yet been completed. The complexities of bone and calcium metabolism have been and remain, to many people, somewhat mysterious and a daunting task to understand. This book is designed to try to unravel those mysteries and present them in an interesting and comprehensible manner.

Physiology of Calcium, Phosphate, Magnesium and Vitamin D.

The physiology of calcium and the other minerals involved in its metabolism is complex and intimately linked to the physiology of bone. Five principal humoral factors are involved in maintaining plasma concentrations of calcium, magnesium and phosphate and in coordinating the balance between their content in bone. The transmembrane transport of these elements is dependent on a series of complex mechanisms that are partly controlled by these hormones. The plasma concentration of calcium is initially sensed by a calcium-sensing receptor, which then sets up a cascade of events that initially determines parathyroid hormone secretion and eventually results in a specific action within the target organs, mainly bone and kidney. This chapter describes the physiology of these humoral factors and relates them to the pathological processes that give rise to disorders of calcium, phosphate and magnesium metabolism as well as of bone metabolism. This chapter also details the stages in the calcium cascade, describes the effects of calcium on the various target organs, gives details of the processes by which phosphate and magnesium are controlled and summarises the metabolism of vitamin D. The pathology of disorders of bone and calcium metabolism is described in detail in the relevant chapters.

A Practical Approach to Vitamin D Deficiency and Rickets.

Rickets is a condition in which there is failure of the normal mineralisation (osteomalacia) of growing bone. Whilst osteomalacia may be present in adults, rickets cannot occur. It is generally caused by a lack of mineral supply, which can either occur as a result of the deficiency of calcium (calciopaenic rickets, now known as parathyroid hormone-dependent rickets) or of phosphate (phosphopaenic rickets, now called FGF23-dependent rickets). Renal disorders may also interfere with the process of mineralisation and cause rickets. Only parathyroid hormone-dependent rickets and distal renal tubular disorders will be discussed in this chapter. The most common cause of rickets is still vitamin D deficiency, which is also responsible for other problems. Disorders of vitamin D metabolism or responsiveness may also cause similar issues. Distal renal tubular acidosis may also be caused by a variety of metabolic errors similar to those of osteoclasts. One form of distal renal tubular acidosis also causes a type of osteopetrosis. This chapter describes these conditions in detail and sets out a logical approach for treatment.

Classification of Disorders of Bone and Calcium Metabolism.

Classification is a natural human trait that enables us to put what may otherwise be very complex subjects into some order. However, classification should be seen not as an end in itself but rather as a means to help us understand certain topics. In the case of medicine, classification helps to provide information about the causes underlying many of the conditions encountered and, in some cases, provides a rationale for developing new treatments. This chapter aims to provide a helpful (if complex) classification of diseases of bone and calcium and, where known, to describe the underlying genetic mechanisms.

Case Histories.

Conditions related to abnormalities of calcium and bone metabolism are large in number and are characterised by hypocalcaemia, hypercalcaemia, primary and secondary osteoporosis, rickets resulting from both vitamin D and phosphate metabolism disorders, and a series of miscellaneous conditions. Included in this chapter is a series of cases drawn from our clinics and from colleagues who have presented these clinical problems at the recent Advanced Courses in Paediatric Bone and Calcium Metabolism run by the British Paediatric and Adolescent Bone group. This series of cases is not fully comprehensive but is designed to cover the major aspects of bone- and calcium-related disorders.

Anticonvulsant treatment associated with intractable hypocalcaemia in a female child with hypoparathyroidism.

BACKGROUND: We report the case of a female infant with hypoparathyroidism due to an activating mutation in the calcium-sensing receptor gene. CASE REPORT: The child presented in the neonatal period with clinical seizures associated with severe hypocalcaemia, hyperphosphataemia, low parathyroid hormone levels and elevated urine calcium:creatinine ratios. She required intravenous calcium and phenobarbitone initially, and then oral 1-alfacalcidol (1-AC) and phenobarbitone were started. The patient had intractable hypocalcaemia in the first 5 months of life despite escalating doses of 1-AC. When the phenobarbitone was stopped at 5 months of age she was admitted soon after with symptomatic hypercalcaemia. We postulate that the phenobarbitone increased the metabolism of 1-AC and thus she needed large doses of 1-AC to treat hypocalcaemia until the phenobarbitone was stopped. Her parents had no biochemical abnormalities on testing. RESULTS: Molecular genetic analysis confirmed that our patient had a de novo missense variant, c.682G>A (p.Glu228Lys) in exon 4 of the calcium-sensing receptor. CONCLUSION: This case report highlights the importance that clinicians caring for children on vitamin D and its analogues are aware of the interaction with phenobarbitone, which can result in symptomatic hypocalcaemia. 1-AC should be stored at 2-8°C, otherwise it will be rendered inactive.