Early Life Management of Osteogenesis Imperfecta

PURPOSE OF REVIEW

This review aims to provide a review of the multidisciplinary management of infants with osteogenesis imperfecta (OI) during the first year of life, focusing on those with severe disease. The authors draw on published literature and direct experience of working in a large paediatric centre specialising in the management of rare bone disease.

RECENT FINDINGS

Whilst understanding of the pathophysiology of OI has grown over the past decade, the evidence base for management of infants remains limited. There has been a greater recognition of certain subjects of concern including pain management, cervical spine deformity, and neurocognitive development. Both international consensus guidelines on rehabilitation and disease-specific growth charts have been welcomed by clinical teams. The early involvement of multidisciplinary specialist care is critical in ensuring optimal care for the infant with severe OI. A long-term perspective which focuses on the axial, craniofacial, and peripheral skeleton as well as on development more generally provides a framework which can guide the management of infants with severe OI.

New diagnostic modalities and emerging treatments for neonatal bone disease

Bone disease in the neonatal period has often been regarded as an issue affecting premature infants, or a collection of rare and ultra-rare disorders that most neonatologists will see only once or twice each year, or possibly each decade. The emergence of targeted therapies for some of these rare disorders means that neonatologists may be faced with diagnostic dilemmas that need a rapid solution in order to access management options that did not previously exist. The diagnostic modalities available to the neonatologist have not changed a great deal in recent years; blood tests and radiographs still form the mainstays with other techniques usually reserved for research studies, but rapid access to genomic testing is emergent. This paper provides an update around diagnosis and management of bone problems likely to present to the neonatologist.

Early life vitamin D depletion alters the postnatal response to skeletal loading in growing and mature bone

There is increasing evidence of persistent effects of early life vitamin D exposure on later skeletal health; linking low levels in early life to smaller bone size in childhood as well as increased fracture risk later in adulthood, independently of later vitamin D status. A major determinant of bone mass acquisition across all ages is mechanical loading. We tested the hypothesis in an animal model system that early life vitamin D depletion results in abrogation of the response to mechanical loading, with consequent reduction in bone size, mass and strength during both childhood and adulthood. A murine model was created in which pregnant dams were either vitamin D deficient or replete, and their offspring moved to a vitamin D replete diet at weaning. Tibias of the offspring were mechanically loaded and bone structure, extrinsic strength and growth measured both during growth and after skeletal maturity. Offspring of vitamin D deplete mice demonstrated lower bone mass in the non loaded limb and reduced bone mass accrual in response to loading in both the growing skeleton and after skeletal maturity. Early life vitamin D depletion led to reduced bone strength and altered bone biomechanical properties. These findings suggest early life vitamin D status may, in part, determine the propensity to osteoporosis and fracture that blights later life in many individuals.

Correlation of VEGF production with IL1 alpha and IL6 secretion by human pituitary adenoma cells

OBJECTIVES

Vascular endothelial growth factor (VEGF) is considered to be the most important angiogenic factor involved in the neovascularisation of solid tumours. Regulatory molecules include cytokines and growth factors. Interleukin (IL)1 and IL6 have both been shown to regulate VEGF levels in a variety of tissues. The role of cytokines in the pathogenesis of pituitary tumours remains unclear. We have examined the expression of VEGF and its relationships with IL1 and IL6 in the human pituitary tumour cell line HP75 and a series of human pituitary tumours. We have also looked at the relationship of tumour volume and invasive status to VEGF secretion.

METHODS

Surgically resected tumours were routinely cultured in single-cell suspension at 200 K/well (standard unit for culture of dispersed primary pituitary adenoma cells). We measured VEGF, IL1 alpha and IL6 levels by ELISA. Tumour volume and invasion grade were assessed by preoperative magnetic resonance imaging.

RESULTS

VEGF was detected in conditioned medium of HP75 cells (900+/-52 pg/ml) and in 82% of tumours tested (range 26-16 464 pg/ml). Tumour volume and secretion of VEGF were significantly associated with levels of IL6 (volume, P = 0.056; VEGF, P < 0.001 (P values based on Spearman's test)) and IL1 alpha produced (volume, P < 0.005; VEGF, P < 0.001). Invasive tumours showed a higher basal secretion of VEGF that that of the non-invasive type; however, this difference was not significant. Addition of exogenous IL1 alpha, but not IL6, significantly increased VEGF production.

CONCLUSIONS

The significant associations between VEGF and the levels of IL6 and IL1 alpha suggest an important role for these cytokines in the development of these tumours.

Expression of interleukin-6 and its effects on growth of HP75 human pituitary tumor cells

The role of IL-6 in the pathogenesis of pituitary adenomas is unclear, as tumor biology is difficult to study in primary culture. We have shown here that the human pituitary cell line HP75 synthesizes IL-6 mRNA and expresses and secretes IL-6 (6167 +/- 56 pg/ml/72 h for 30,000 cells). IL-6 receptor (IL-6R) mRNA was identified by in situ hybridization and RT-PCR. Exogenous IL-6 in low dose (1 ng/ml) stimulated, whereas higher doses (100 ng/ml) inhibited, growth. This diverse effect occurs in other cell types as a result of receptor down-regulation. Cell growth was inhibited by IL-6-blocking antibody (76 +/- 6.5% inhibition; P < 0.0001). This demonstrates that IL-6 is an important growth regulator in HP75 cells, having an autocrine growth stimulatory effect under basal conditions. IL-1alpha and dibutyryl cAMP stimulated and dexamethasone inhibited IL-6 secretion; however, bacterial lipopolysaccharide, forskolin, and cholera toxin had no effect. This implies that there is a defect in the control of IL-6 secretion. Soluble IL-6R was not detected, but soluble gp130 receptor was present in the conditioned medium. Stimulation of cleavage of soluble IL-6R from the membrane-bound IL-6R could not be induced by phorbol ester or dexamethasone. Whether IL-6 has a similar effect in human pituitary adenomas requires further investigation.

Congenital avalvular pulmonary artery and infantile lobar emphysema. A diagnostic correlation

Some cardiovascular lesions may result in tracheobronchial obstruction and many of these will commonly be associated with infantile lobar emphysema (ILE). By contrast a relatively smaller percentage of cases of ILE results from vascular compression. We offer a new term, "congenital avalvular pulmonary artery (CAPA)," to describe the complex of the absent pulmonary valve and the concomitant marked pulmonary artery dilatation because CAPA is more descriptively inclusive of the abnormality of the artery beyond the valve. The diagnostic correlation of CAPA and ILE is of considerable importance since the initial presentation of CAPA is usually as ILE and the recognition of a triangular or rounded hilar density should raise suspicion for CAPA even before clinical signs become evident. Differential diagnosis must include other causes of ILE including infantile lobar emphysema with bronchial atresia.