Nutritional hypophosphatemic rickets secondary to Neocate® use.

Elemental formula is commonly used in children with feeding intolerance. We describe two, medically complex and feeding tube dependent, patients exclusively fed with Neocate® who subsequently developed hypophosphatemic rickets. Both patients had gross motor decline and pain with physical touch. They were found to have low serum phosphorus, normal calcium, and vitamin D studies, with elevated alkaline phosphatase suggestive of nutritional hypophosphatemia. Both courses were complicated by hypocalcemia following formula change and phosphorus supplementation, highlighting the need for careful management of phosphate repletion in affected individuals. Diligent serial electrolyte monitoring as well as attention to bone health is needed in conjunction with elemental nutrition. Formula change led to restoration of calcium and phosphorus homeostasis and radiographic improvement in these patients.

Evaluating RANKL and OPG levels in patients with Duchenne muscular dystrophy.

RANKL-OPG should be explored in DMD patients to potentially provide targeted therapy. We quantified RANKL and OPG levels in DMD patients compared with controls. RANKL, OPG, and RANKL:OPG significantly declined with age in DMD patients suggesting some bone turnover markers are difficult to assess or use as therapeutic indicators. INTRODUCTION: Osteoporosis in Duchenne muscular dystrophy (DMD) is multi-factorial in nature with high prevalence of fractures. RANKL-OPG should be explored to potentially provide targeted therapy for these patients. We quantified RANKL, OPG, and RANKL:OPG levels in DMD patients compared with controls and analyzed the influence of age, glucocorticoid use, ambulatory status, bone density, and fracture history. METHODS: DMD patients were enrolled at CHLA. Controls were recruited from general pediatric clinic and in collaboration with samples from a previously completed study. Free soluble RANKL and OPG levels were quantified using a sandwich ELISA. RESULTS: Fifty DMD patients and 50 controls were enrolled. DMD patients had a significant decline in RANKL, OPG, and RANKL:OPG with age (p = < 0.0001, p = 0.026, and p = 0.002, respectively) while healthy controls showed no significant change. RANKL trended lower in patients on glucocorticoids (p = 0.05), attributed to the significantly older age in the treatment group. RANKL and RANKL:OPG levels were significantly lower in the non-ambulatory group compared with the ambulatory group (p = 0.010 and 0.036 respectively), again likely due to their older age. There was no correlation of RANKL, OPG, or RANKL:OPG with DXA Z-score or presence of vertebral fractures. CONCLUSION: There was significant decline in RANKL, OPG, and RANKL:OPG with age in DMD patients compared with controls, potentially due to disease severity or worsening osteoblastic function. This suggests some bone turnover markers may be difficult to assess or use as therapeutic indicators in DMD patients. Larger studies are needed to evaluate the role of RANKL-OPG in DMD patients to provide better targeted therapy.

Bisphosphonate therapy in an infant with generalized arterial calcification with an ABCC6 mutation.

Generalized arterial calcification of infancy (GACI) is a rare genetic disorder with high infantile mortality, described to be due to ENPP1, and less commonly ABCC6 mutations. Bisphosphonate treatment has been described to improve survival in ENPP1-positive GACI patients, but few studies have described bisphosphonate treatment in ABCC6-positive patients. Without therapy, patients will die before 6 months of age. Our patient is now 3 years old, former recipient twin of twin-to-twin transfusion syndrome (TTTS). Initial fetal echocardiogram at 19 weeks showed calcifications of the ascending aorta and pulmonary artery (PA). She underwent utero laser therapy, and despite resolution of the TTTS, her follow-up scans showed progressive calcification of the aorta and PA. Postnatal echocardiogram showed calcification and supravalvar stenosis of the aorta and PA. CT on day of life 6 showed calcifications in the PAs, aortic arch, and descending aorta. Quantification of valvular calcification can be difficult; in our patient, increasing outflow tract gradient on echocardiogram was used to monitor disease progression. Molecular testing revealed an ABCC6 gene mutation. She was started on weekly IV pamidronate (0.1-0.3 mg/kg/week) on day 8 of life then transitioned to oral etidronate (15-20 mg/kg/day). Given progressive supravalvar aortic and pulmonary stenosis, she underwent surgical repair with patch augmentation of the PA and ascending aorta at 4 months old. She has done well post-operatively, continuing on enteral bisphosphonate therapy with no side effects to date. Her identical twin was confirmed to have the same mutation and remains asymptomatic with no calcifications. Aggressive bisphosphonate therapy should be started as soon as possible in patients with infantile arterial calcinosis due to ABCC6 or ENPP1 mutations. Echocardiographic evaluation can be used to monitor disease progression by arterial gradients. Molecular testing is also essential to evaluate for possible co-morbidities in these patients and pregnancy management for the future.