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Mutations in the Wnt co-receptor, LRP5 , lead to skeletal diseases in humans. Matthew Warman and his colleagues have now developed mutant mice with tissue-specific alterations of Lrp5 expression and found that these mice phenocopy the human skeletal diseases. They also found that Lrp5 acts locally to affect bone homeostasis. Their data suggest that increasing LRP5 signaling in mature bone cells may be a strategy to treat osteoporosis. The human skeleton is affected by mutations in low-density lipoprotein receptor-related protein 5 (LRP5). To understand how LRP5 influences bone properties, we generated mice with osteocyte-specific expression of inducible Lrp5 mutations that cause high and low bone mass phenotypes in humans. We found that bone properties in these mice were comparable to bone properties in mice with inherited mutations. We also induced an Lrp5 mutation in cells that form the appendicular skeleton but not in cells that form the axial skeleton; we observed that bone properties were altered in the limb but not in the spine. These data indicate that Lrp5 signaling functions locally, and they suggest that increasing LRP5 signaling in mature bone cells may be a strategy for treating human disorders associated with low bone mass, such as osteoporosis.

Purpose Generalized arterial calcification of infancy (GACI), characterized by vascular calcifications that are often fatal shortly after birth, is usually caused by deficiency of ENPP1. A small fraction of GACI cases result from deficiency of ABCC6, a membrane transporter. The natural history of GACI survivors has not been established in a prospective fashion. Methods We performed deep phenotyping of 20 GACI survivors. Results Sixteen of 20 subjects presented with arterial calcifications, but only 5 had residual involvement at the time of evaluation. Individuals with ENPP1 deficiency either had hypophosphatemic rickets or were predicted to develop it by 14 years of age; 14/16 had elevated intact FGF23 levels (iFGF23). Blood phosphate levels correlated inversely with iFGF23. For ENPP1-deficient individuals, the lifetime risk of cervical spine fusion was 25%, that of hearing loss was 75%, and the main morbidity in adults was related to enthesis calcification. Four ENPP1-deficient individuals manifested classic skin or retinal findings of PXE. We estimated the minimal incidence of ENPP1 deficiency at ~1 in 200,000 pregnancies. Conclusion GACI appears to be more common than previously thought, with an expanding spectrum of overlapping phenotypes. The relationships among decreased ENPP1, increased iFGF23, and rickets could inform future therapies.

Abstract Context The reproductive axis is controlled by a network of gonadotropin-releasing hormone (GnRH) neurons born in the primitive nose that migrate to the hypothalamus alongside axons of the olfactory system. The observation that congenital anosmia (inability to smell) is often associated with GnRH deficiency in humans led to the prevailing view that GnRH neurons depend on olfactory structures to reach the brain, but this hypothesis has not been confirmed. Objective The objective of this work is to determine the potential for normal reproductive function in the setting of completely absent internal and external olfactory structures. Methods We conducted comprehensive phenotyping studies in 11 patients with congenital arhinia. These studies were augmented by review of medical records and study questionnaires in another 40 international patients. Results All male patients demonstrated clinical and/or biochemical signs of GnRH deficiency, and the 5 men studied in person had no luteinizing hormone (LH) pulses, suggesting absent GnRH activity. The 6 women studied in person also had apulsatile LH profiles, yet 3 had spontaneous breast development and 2 women (studied from afar) had normal breast development and menstrual cycles, suggesting a fully intact reproductive axis. Administration of pulsatile GnRH to 2 GnRH-deficient patients revealed normal pituitary responsiveness but gonadal failure in the male patient. Conclusions Patients with arhinia teach us that the GnRH neuron, a key gatekeeper of the reproductive axis, is associated with but may not depend on olfactory structures for normal migration and function, and more broadly, illustrate the power of extreme human phenotypes in answering fundamental questions about human embryology.

As pediatric populations in the United States (US) become increasingly diverse, current practices for interpreting bone density using DXA in children warrant reevaluation. The International Society for Clinical Densitometry currently recommends adjusting pediatric bone density Z-scores by race, sex, and age. However, race-based adjustments risk reinforcing disparities and perpetuating systemic inequities in pediatric bone health assessment. We conducted a scoping review of studies examining racial and ethnic differences in BMD among healthy US children, identifying 3960 records across 4 databases, of which 54 met inclusion criteria. Across these studies, reporting of race and ethnicity was inconsistent: although nearly all relied on self- or parent-report, none provided explicit definitions, and only 13% confirmed concordance across grandparents. Fifty percent of studies reported statistically significant racial differences in BMD, yet most did so without comprehensive covariate adjustment. By contrast, studies that accounted for height, lean mass, and pubertal status frequently found that differences attenuated or disappeared. These findings underscore the need to critically reconsider race-based adjustments in pediatric DXA interpretation. Developing and validating race-neutral reference standards, with attention to structural determinants and biologically relevant measures, such as stature, body composition, and pubertal timing, is essential for achieving a more equitable and clinically meaningful assessment of pediatric bone health.

Some patients with Turner syndrome have a karyotype showing mosaicism. This article describes the case of a boy with 45,X0/46,XY mosaicism, often referred to as mixed gonadal dysgenesis, who was evaluated for short stature. Different types of Turner syndrome mosaicism and their associated phenotypes, as well as the management of short stature in these patients, are discussed. Background An 8.5-year-old boy was referred to a pediatric endocrinology clinic for evaluation of short stature. At birth, a chordee without hypospadius, 90-degree penile torsion and an undescended testis on the right had been observed. The boy had undergone surgical repair at 1 year of age and at that time an undescended 'nonfunctional' streak gonad and a horseshoe kidney had been noted. Subsequent karyotype analysis had revealed a 45,X0/46,XY karyotype with mosaicism. Since 4–5 years of age, the patient's height has been below the 3 rd percentile, whereas his weight has been maintained at approximately the 3 rd percentile. Investigations Performance of thyroid function tests, measurement of levels of insulin-like growth factor I and insulin-like growth factor binding protein 3, estimation of bone age, calculation of height and weight percentiles and SD scores based on 2000 normative data from the National Center for Health Statistics, USA. Diagnosis Mixed gonadal dysgenesis with a 45,X0/46,XY karyotype. Management The patient's growth was found to be following the 50 th percentile growth curve on the Turner syndrome growth chart, which was significantly below his mid-parental target height. He was started on growth hormone at a dose of 0.35 mg/kg/week. The patient remains under close follow-up to monitor his linear growth velocity and his pubertal development.

Human height can be divided into sitting height and leg length, reflecting growth of different parts of the skeleton whose relative proportions are captured by the ratio of sitting to total height (as sitting height ratio, SHR). Height is a highly heritable trait, and its genetic basis has been well-studied. However, the genetic determinants of skeletal proportion are much less well-characterized. Expanding substantially on past work, we performed a genome-wide association study (GWAS) of SHR in ∼450,000 individuals with European ancestry and ∼100,000 individuals with East Asian ancestry from the UK and China Kadoorie Biobanks. We identified 565 loci independently associated with SHR, including all genomic regions implicated in prior GWAS in these ancestries. While SHR loci largely overlap height-associated loci (P < 0.001), the fine-mapped SHR signals were often distinct from height. We additionally used fine-mapped signals to identify 36 credible sets with heterogeneous effects across ancestries. Lastly, we used SHR, sitting height, and leg length to identify genetic variation acting on specific body regions rather than on overall human height.