The impact of caregiving for children with chronic conditions on the HPA axis: A scoping review.

Caregiving has been robustly linked to caregiver health through the dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis in the context of caregiving for an adult with a chronic illness. However, little research examines the physiological impact of caregiving for a child with a chronic illness despite high burden and unique stressors. In this review, we explore the links of caregiving for a child with a congenital, chromosomal, or genetic disorder to the regulation or dysregulation of the HPA axis. A search was conducted in PubMed, Embase, and the Web of Science and 15 studies met inclusion criteria. Overall, there were inconsistent links of caregiving to HPA axis functioning, perhaps due to the heterogeneity across disease contexts, study designs, and biomarker measurement. Future research should standardize measurement and study designs, increase participant diversity, and examine moderators of the links of caregiving to the HPA axis.

A neomorphic variant in SP7 alters sequence specificity and causes a high-turnover bone disorder.

SP7/Osterix is a transcription factor critical for osteoblast maturation and bone formation. Homozygous loss-of-function mutations in SP7 cause osteogenesis imperfecta type XII, but neomorphic (gain-of-new-function) mutations of SP7 have not been reported in humans. Here we describe a de novo dominant neomorphic missense variant (c.926 C > G:p.S309W) in SP7 in a patient with craniosynostosis, cranial hyperostosis, and long bone fragility. Histomorphometry shows increased osteoblasts but decreased bone mineralization. Mice with the corresponding variant also show a complex skeletal phenotype distinct from that of Sp7-null mice. The mutation alters the binding specificity of SP7 from AT-rich motifs to a GC-consensus sequence (typical of other SP family members) and produces an aberrant gene expression profile, including increased expression of Col1a1 and endogenous Sp7, but decreased expression of genes involved in matrix mineralization. Our study identifies a pathogenic mechanism in which a mutation in a transcription factor shifts DNA binding specificity and provides important in vivo evidence that the affinity of SP7 for AT-rich motifs, unique among SP proteins, is critical for normal osteoblast differentiation.

Laser Capture Microdissection of Mouse Growth Plate Cartilage.

The ability to identify, isolate, and study pure populations of cells is critical for understanding normal physiology in organs and tissues, which involves spatial regulation of signaling pathways and interactions between cells with different functions, expression profiles, and lineages. Here, we focus on assessing the growth plate cartilage, composed of multiple functionally and histologically distinct zones, to investigate temporally and spatially dependent gene expression differences. In this chapter, we describe the method of laser capture microdissection to isolate chondrocytes from different zones of differentiation in the mouse growth plate cartilage for RNA isolation, and subsequent downstream applications, such as RNA-sequencing and quantitative real-time PCR. We also provide an assessment of different factors contributing to the integrity of the isolated RNA, such as staining methods and procedures in RNA isolation.

Persistent Sox9 expression in hypertrophic chondrocytes suppresses transdifferentiation into osteoblasts.

Longitudinal bone growth is driven by endochondral ossification, a process in which cartilage tissue is generated by growth plate chondrocytes and then remodeled into bone by osteoblasts. In the postnatal growth plate, as hypertrophic chondrocytes approach the chondro-osseous junction, they may undergo apoptosis, or directly transdifferentiate into osteoblasts. The molecular mechanisms governing this switch in cell lineage are poorly understood. Here we show that the physiological downregulation of Sox9 in hypertrophic chondrocyte is associated with upregulation of osteoblast-associated genes (such as Mmp13, Cola1, Ibsp) in hypertrophic chondrocytes, before they enter the metaphyseal bone. In transgenic mice that continued to express Sox9 in all cells derived from the chondrocytic lineage, upregulation of these osteoblast-associated genes in the hypertrophic zone failed to occur. Furthermore, lineage tracing experiments showed that, in transgenic mice expressing Sox9, the number of chondrocytes transdifferentiating into osteoblasts was markedly reduced. Collectively, our findings suggest that Sox9 downregulation in hypertrophic chondrocytes promotes expression of osteoblast-associated genes in hypertrophic chondrocytes and promotes the subsequent transdifferentiation of these cells into osteoblasts.

Effect of Genetic Diagnosis on Patients with Previously Undiagnosed Disease.

BACKGROUND: Many patients remain without a diagnosis despite extensive medical evaluation. The Undiagnosed Diseases Network (UDN) was established to apply a multidisciplinary model in the evaluation of the most challenging cases and to identify the biologic characteristics of newly discovered diseases. The UDN, which is funded by the National Institutes of Health, was formed in 2014 as a network of seven clinical sites, two sequencing cores, and a coordinating center. Later, a central biorepository, a metabolomics core, and a model organisms screening center were added. METHODS: We evaluated patients who were referred to the UDN over a period of 20 months. The patients were required to have an undiagnosed condition despite thorough evaluation by a health care provider. We determined the rate of diagnosis among patients who subsequently had a complete evaluation, and we observed the effect of diagnosis on medical care. RESULTS: A total of 1519 patients (53% female) were referred to the UDN, of whom 601 (40%) were accepted for evaluation. Of the accepted patients, 192 (32%) had previously undergone exome sequencing. Symptoms were neurologic in 40% of the applicants, musculoskeletal in 10%, immunologic in 7%, gastrointestinal in 7%, and rheumatologic in 6%. Of the 382 patients who had a complete evaluation, 132 received a diagnosis, yielding a rate of diagnosis of 35%. A total of 15 diagnoses (11%) were made by clinical review alone, and 98 (74%) were made by exome or genome sequencing. Of the diagnoses, 21% led to recommendations regarding changes in therapy, 37% led to changes in diagnostic testing, and 36% led to variant-specific genetic counseling. We defined 31 new syndromes. CONCLUSIONS: The UDN established a diagnosis in 132 of the 382 patients who had a complete evaluation, yielding a rate of diagnosis of 35%. (Funded by the National Institutes of Health Common Fund.).

Differential aging of growth plate cartilage underlies differences in bone length and thus helps determine skeletal proportions.

Bones at different anatomical locations vary dramatically in size. For example, human femurs are 20-fold longer than the phalanges in the fingers and toes. The mechanisms responsible for these size differences are poorly understood. Bone elongation occurs at the growth plates and advances rapidly in early life but then progressively slows due to a developmental program termed "growth plate senescence." This developmental program includes declines in cell proliferation and hypertrophy, depletion of cells in all growth plate zones, and extensive underlying changes in the expression of growth-regulating genes. Here, we show evidence that these functional, structural, and molecular senescent changes occur earlier in the growth plates of smaller bones (metacarpals, phalanges) than in the growth plates of larger bones (femurs, tibias) and that this differential aging contributes to the disparities in bone length. We also show evidence that the molecular mechanisms that underlie the differential aging between different bones involve modulation of critical paracrine regulatory pathways, including insulin-like growth factor (Igf), bone morphogenetic protein (Bmp), and Wingless and Int-1 (Wnt) signaling. Taken together, the findings reveal that the striking disparities in the lengths of different bones, which characterize normal mammalian skeletal proportions, is achieved in part by modulating the progression of growth plate senescence.