X-linked hypophosphatemia caused by a deep intronic variant in PHEX identified by PCR-based RNA analysis of urine-derived cells.

X-linked hypophosphatemia (XLH) is caused by dominant inactivating mutations in the phosphate regulating endopeptidase homology, X-linked (PHEX), resulting in elevated fibroblast growth factor 23 (FGF23), hypophosphatemia, rickets and osteomalacia. PHEX variants are identified in approximately 85 % of individuals with XLH, which leaves a substantial proportion of patients with negative DNA-based genetic testing. Here we describe a 16-year-old male who had typical features of XLH on clinical and radiological examination. Genomic DNA sequencing of a hypophosphatemia gene panel did not reveal a pathogenic variant. We therefore obtained a urine sample, established cell cultures and obtained PHEX cDNA from urine-derived cells. Sequencing of exon-spanning PCR products demonstrated the presence of an 84 bp pseudoexon in PHEX intron 21 due to a deep intronic variant (c.2147+1197A>G), which created a new splice donor site in intron 21. The corresponding PHEX protein would lack 33 amino acids on the C-terminus and instead include an unrelated sequence of 17 amino acids. The patient and his affected mother both had this variant. This report highlights that individuals with the typical clinical characteristics of XLH and negative genomic DNA sequence analysis can have deep intronic PHEX variants that are detectable by PCR-based RNA diagnostics.

Leuprolide Acetate and QTc Interval in Gender-Diverse Youth.

Background: Puberty suppression is a standard of care for gender-affirming therapy in gender-diverse youth. Leuprolide acetate is a gonadotropin-releasing hormone agonist (GnRHa) commonly used for pubertal suppression. There are concerns that GnRHa agents prolong the rate-corrected QT interval (QTc) when used as androgen deprivation therapy in management of prostate cancer; however, there is a paucity of literature regarding the effect of leuprolide acetate on QTc intervals in gender-diverse youth. Aim: To determine the proportion of gender-diverse youth with QTc prolongation on leuprolide acetate therapy. Methods: A retrospective chart review of gender-diverse youth initiated on leuprolide acetate between July 1, 2018 and December 31, 2019 was conducted at a tertiary care pediatric hospital in Alberta, Canada. Youth aged 9-18 years were included if a 12-lead electrocardiogram was completed after initiating leuprolide acetate. The proportion of adolescents with clinically significant QTc prolongation was assessed, defined as QTc >460 milliseconds (ms). Results: Thirty-three pubertal youth were included. The cohort had a mean age of 13.7 years (standard deviation [SD] 2.1) and 69.7% identified as male (assigned female at birth). The mean post-leuprolide acetate QTc was 415 ms (SD 27, range 372-455). Twenty-two (66.7%) of youth were prescribed concomitant medications, including QTc-prolonging medications in 15.2%. None of the 33 youth on leuprolide acetate had QTc prolongation. Only 24.2% patients had a borderline QTc (QTc 440-460 ms). Conclusion: No gender-diverse youth on leuprolide acetate demonstrated clinically significant QTc prolongation.

X-linked hypophosphatemia, fibroblast growth factor 23 signaling, and craniosynostosis.

This review summarizes the current knowledge of fibroblast growth factor 23 signaling in bone and its role in the disease pathology of X-linked hypophosphatemia. Craniosynostosis is an under-recognized complication of X-linked hypophosphatemia. The clinical implications and potential cellular mechanisms invoked by increased fibroblast growth factor 23 signaling causing craniosynostosis are reviewed. Knowledge gaps are identified and provide direction for future clinical and basic science studies.

Regulation of 1 and 24 hydroxylation of vitamin D metabolites in the proximal tubule.

Calcium and phosphate are critical for numerous physiological processes. Consequently, the plasma concentration of these ions are tightly regulated. Calcitriol, the active form of vitamin D, is a positive modulator of mineralization as well as calcium and phosphate metabolism. The molecular and physiological effects of calcitriol are well documented. Calcitriol increases blood calcium and phosphate levels by increasing absorption from the intestine, and resorption of bone. Calcitriol synthesis is a multistep process. A precursor is first made via skin exposure to UV, it is then 25-hydroxylated in the liver to form 25-hydroxyitamin D. The next hydroxylation step occurs in the renal proximal tubule via the 1-αhydroxylase enzyme (encoded by CYP27B1) thereby generating 1,25-dihydroxyvitamin D, that is, calcitriol. At the same site, the 25-hydroxyvitamin D 24-hydroxlase enzyme encoded by CYP24A1 can hydroxylate 25-hydroxyvitamin D or calcitriol to deactivate the hormone. Plasma calcitriol levels are primarily determined by the regulated expression of CYP27B1 and CYP24A1. This occurs in response to parathyroid hormone (increases CYP27B1), calcitriol itself (decreases CYP27B1 and increases CYP24A1), calcitonin (increases or decreases CYP24A1 and increases CYP27B1), FGF23 (decreases CYP27B1 and increases CYP24A1) and potentially plasma calcium and phosphate levels themselves (mixed effects). Herein, we review the regulation of CYP27B1 and CYP24A1 transcription in response to the action of classic phophocalciotropic hormones and explore the possibility of direct regulation by plasma calcium.

Metaphyseal and posterior rib fractures in osteogenesis imperfecta: Case report and review of the literature.

PURPOSE: Metaphyseal corner fractures and posterior rib fractures are thought to only occur in settings of inflicted injury. We describe a case of siblings who presented with metaphyseal corner fractures and multiple posterior rib fractures who were later found to carry FKBP10 mutations, a rare cause of Osteogenesis Imperfecta (OI) known as Bruck syndrome. This clinical presentation led to a literature review examining fracture types in OI and inflicted injury. CASES: A 15-month-old male presented with multiple healing fractures of varying ages including posterior rib and metaphyseal corner fractures with no history of significant trauma. He had joint laxity, short stature and Wormian bones. His diagnosis of Bruck Syndrome led to investigations in his sibling at birth, which demonstrated the same fracture pattern including multiple posterior rib and metaphyseal corner fractures. They both had pathogenic compound heterozygous FKBP10 variants. LITERATURE REVIEW AND RESULTS: We performed a literature review evaluating the fracture pattern in cases investigated for inflicted injury and found to have OI. Fourteen articles reported 78 children with OI initially diagnosed as inflicted injury. Of these children, 71 (91%) were diagnosed with milder forms of OI (Sillence type I and IV). Sixty-four children (81%) had clinical signs of OI including blue sclera, dentinogenesis imperfecta, short stature, joint laxity and limb bowing. Fifteen (19%) children had fractures of high specificity for inflicted injury including metaphyseal corner fractures and posterior rib fractures and 58 (74%) had fractures of moderate specificity for inflicted injury such as bilateral fractures and fractures of different ages. CONCLUSION: Metaphyseal corner fractures and posterior rib fractures are highly associated with inflicted injury, but they have been reported in children with OI. Bruck syndrome, a rare and severe form of OI can present with metaphyseal and posterior rib fractures, including at birth. When features of OI are present in children with metaphyseal corner fractures and/or posterior rib fractures are present, genetic testing may be warranted.

Incidence and Risk Factors for Hypoglycemia During Fetal-to-Neonatal Transition in Premature Infants.

Objective: To determine the incidence and risk factors associated with neonatal hypoglycemia in the premature population <33 weeks' gestation. Methods: This was a secondary retrospective analysis from previous infants enrolled in randomized controlled trials. A total of 255 infants <33 weeks' gestation were born during the study period. Eight infants were excluded due to missing glucose or maternal data and 175 infants were analyzed. Main outcome measures: Primary outcome was hypoglycemia (blood glucose <2.6mmol/L) determined via glucose oxidase method on arterial or venous blood gas. Birth weight subgroups: small for gestational age (SGA, birth weight <10%ile for gestational age) and large for gestational age (LGA, birth weight >90%ile for gestational age). Maternal hypertension was systolic blood pressure >140mmHg. Results: 175 infants <33 weeks' gestational age (89 male, 84 female) were analyzed. Hypoglycemia occurred in 59 infants (33.7%). Maternal hypertension (OR 3.07, 95% CI 1.51-6.30, p = 0.002) was the sole risk factor for neonatal hypoglycemia. Protective factors for hypoglycemia included labor at time of delivery (OR 4.51, 95% CI 2.29-9.18, p <0.0001) and antenatal magnesium sulfate (OR 2.53, 95% CI 1.23-5.50, p = 0.01). There were no significant differences between hypoglycemic and euglycemic infants in sex, gestational age, LGA infants, antenatal steroids, vaginal birth, or maternal diabetes. SGA infants were excluded from analysis due to sample size. Conclusions: Premature infants <33 weeks' gestation have increased risk of hypoglycemia. Maternal hypertension increases hypoglycemia risk. Antenatal magnesium sulfate administration or labor at time of delivery decrease hypoglycemia risk.

46,XY disorder of sex development due to 17-beta hydroxysteroid dehydrogenase type 3 deficiency: a plea for timely genetic testing.

BACKGROUND: 17ß-hydroxysteroid dehydrogenase type 3 (17ßHSD3) deficiency is a rare cause of disorder of sex development (DSD) due to impaired conversion of androstenedione to testosterone. Traditionally, the diagnosis was determined by ßHCG-stimulated ratios of testosterone:androstenedione < 0.8. CASE PRESENTATION: An otherwise phenotypically female infant presented with bilateral inguinal masses and a 46,XY karyotype. ßHCG stimulation (1500 IU IM for 2 days) suggested 17ßHSD3 deficiency although androstenedione was only minimally stimulated (4.5 nmol/L to 5.4 nmol/L). Expedient genetic testing for the HSD17B3 gene provided the unequivocal diagnosis. CONCLUSION: We advocate for urgent genetic testing in rare causes of DSD as indeterminate hormone results can delay diagnosis and prolong intervention.

Parenteral and oral antibiotic duration for treatment of pediatric osteomyelitis: a systematic review protocol.

BACKGROUND: Pediatric osteomyelitis is a bacterial infection of bones requiring prolonged antibiotic treatment using parenteral followed by enteral agents. Major complications of pediatric osteomyelitis include transition to chronic osteomyelitis, formation of subperiosteal abscesses, extension of infection into the joint, and permanent bony deformity or limb shortening. Historically, osteomyelitis has been treated with long durations of antibiotics to avoid these complications. However, with improvements in management and antibiotic treatment, standard of care is moving towards short durations of intravenous antibiotics prior to enteral antibiotics. METHODS/DESIGN: The authors will perform a systematic review based on PRISMA guidelines in order to evaluate the literature, looking for evidence to support the optimal duration of parenteral and enteral therapy. The main goals are to see if literature supports shorter durations of either parenteral antibiotics and/or enteral antibiotics.Multiple databases will be investigated using a thorough search strategy. Databases include Medline, Cochrane, EMBASE, SCOPUS, Dissertation Abstracts, CINAHL, Web of Science, African Index Medicus and LILACS. Search stream will include medical subject heading for pediatric patients with osteomyelitis and antibiotic therapy. We will search for published or unpublished randomized and quasi-randomized controlled trials.Two authors will independently select articles, extract data and assess risk of bias by standard Cochrane methodologies. We will analyze comparisons between dichotomous outcomes using risk ratios and continuous outcomes using mean differences. 95% confidence intervals will be computed. DISCUSSION: One of the major dilemmas of management of this disease is the duration of parenteral therapy. Long parenteral therapy has increased risk of serious complications and the necessity for long therapy has been called into question. Our study aims to review the currently available evidence from randomized trials regarding duration of both parenteral and oral therapy for pediatric acute osteomyelitis. TRIAL REGISTRATION: CRD42013002320.

Growth hormone production and action in N1E-115 neuroblastoma cells.

Neuroblastoma cells are undifferentiated cells derived from the neural crest and are commonly used as models for studying neural function. Mouse N1E-115 neuroblastoma cells are derived from cancerous tissue and provide a model for studying the oncogenesis of neural cells. As growth hormone (GH) has been implicated as an autocrine or paracrine involved in neural regulation and in the induction or progression of cancer, the possibility that N1E-115 cells are sites of GH production and GH action was assessed. Using RT-PCR, cultured N1E-115 cells were found to express the mouse GH and GH receptor (GHR) genes. Immunocytochemistry demonstrated that both of the translated proteins (GH and its receptor) were abundantly present in the cytoplasm of these cells and their co-localization was established by confocal cytochemistry. GH action in these cells was determined in cells cultured for 72 h in the presence or absence of 10(-6) M or 10(-9) M mouse GH, which induced neurite sprouting and increased axon growth. In summary, the expression of GH and its receptor in GH responsive tumor-derived N1E-115 neuroblastoma cells suggests they provide a useful experimental model to assess GH actions in neural function or neural oncogenesis.

A high-conductance mode of a poly-3-hydroxybutyrate/calcium/polyphosphate channel isolated from competent Escherichia coli cells.

Reconstitution into planar lipid bilayers of a poly-3-hydroxybutyrate/calcium/polyphosphate (PHB/Ca(2+)/polyP) complex from Escherichia coli membranes yields cationic-selective, 100 pS channels (Das, S., Lengweiler, U.D., Seebach, D. and Reusch, R.N. (1997) Proof for a non-proteinaceous calcium-selective channel in Escherichia coli by total synthesis from (R)-3-hydroxybutanoic acid and inorganic polyphosphate. Proc. Natl. Acad. Sci. USA 94, 9075-9079). Here, we report that this complex can also form larger, weakly selective pores, with a maximal conductance ranging from 250pS to 1nS in different experiments (symmetric 150mM KCl). Single channels were inhibited by lanthanum (IC(50)=42+/-4microM, means+/-S.E.M.) with an unusually high Hill coefficient (8.4+/-1.2). Transition to low-conductance states (<250pS) was favored by increased membrane polarization (/V/ >or=50mV). High conductance states (>250pS) may reflect conformations important for genetic transformability, or "competence", of the bacterial cells, which requires the presence of the PHB/Ca(2+)/polyP complex in the membrane.

A large, voltage-dependent channel, isolated from mitochondria by water-free chloroform extraction.

We examined ion channels derived from a chloroform extract of isolated, dehydrated rat liver mitochondria. The extraction method was previously used to isolate a channel-forming complex containing poly-3-hydroxybutyrate and calcium polyphosphate from Escherichia coli. This complex is also present in eukaryotic membranes, and is located primarily in mitochondria. Reconstituted channels showed multiple subconductance levels and were voltage-dependent, showing an increased probability of higher conductance states at voltages near zero. In symmetric 150 mM KCl, the maximal conductance of the channel ranged from 350 pS to 750 pS. For voltages >+/-60 mV, conductance fluctuated in the range of approximately 50- approximately 200 pS. In the presence of a 1:3 gradient of KCl, at pH = 7.4, selectivity periodically switched between different states ranging from weakly anion-selective (V(rev) approximately -15 mV) to ideally cation-selective (V(rev) approximately +29 mV), without a significant change in its conductance. Overall, the diverse, but highly reproducible, channel activity most closely resembled the behavior of the permeability transition pore channel seen in patch-clamp experiments on native mitoplasts. We suggest that the isolated complex may represent the ion-conducting module from the permeability transition pore.