Amyloid-β neuropathology induces bone loss in male mice by suppressing bone formation and enhancing bone resorption

Alzheimer's disease (AD) and osteoporosis often coexist in the elderly. Although observational studies suggest an association between these two diseases, the pathophysiologic link between AD and skeletal health has been poorly defined. We examined the skeletal phenotype of 5xFAD mice, an AD model with accelerated neuron-specific amyloid-β accumulation causing full-blown AD phenotype by the age of 8 months. Micro-computed tomography indicated significantly lower trabecular and cortical bone parameters in 8-month-old male, but not female, 5xFAD mice than sex-matched wild-type littermates. Dynamic histomorphometry revealed reduced bone formation and increased bone resorption, and quantitative RT-PCR showed elevated skeletal RANKL gene expression in 5xFAD males. These mice also had diminished body fat percentage with unaltered lean mass, as determined by dual-energy X-ray absorptiometry (DXA), and elevated Ucp1 mRNA levels in brown adipose tissue, consistent with increased sympathetic tone, which may contribute to the osteopenia observed in 5xFAD males. Nevertheless, no significant changes could be detected between male 5xFAD and wild-type littermates regarding the serum and skeletal concentrations of norepinephrine. Thus, brain-specific amyloid-β pathology is associated with osteopenia and appears to affect both bone formation and bone resorption. Our findings shed new light on the pathophysiologic link between Alzheimer's disease and osteoporosis.

Venous Thrombosis in a Pseudohypoparathyroidism Patient with a Novel GNAS Frameshift Mutation and Complete Resolution of Vascular Calcifications with Acetazolamide Treatment

INTRODUCTION

Pseudohypoparathyroidism type IA (PHP1A) is characterized by end-organ resistance to multiple hormones and Albright's hereditary osteodystrophy (AHO). PHP1A is caused by inactivating mutations of the GNAS gene encoding the α-subunit of the stimulatory G protein (Gsα). In line with the underlying genetic defect, impaired inhibition of platelet aggregation has been demonstrated in some patients. However, no PHP1A case with thrombotic events has been described. Also, PHP1A cases typically have subcutaneous ossifications, but soft tissue calcifications are another common finding. Treatment options for those and other nonhormonal features of PHP1A are limited.

CASE PRESENTATION

A female patient presented with short stature, fatigue, and exercise-induced carpopedal spasms at age 117/12 years. Diagnosis of PHP1A was made based on hypocalcemia, hyperphosphatemia, elevated serum parathyroid hormone, and AHO features, including short stature and brachydactyly. A novel frameshift variant was detected in the last exon of GNAS (c.1065_1068delGCGT, p.R356Tfs*47), showing complete loss of baseline and receptor-stimulated activity in transfected cells. The patient developed venous thrombosis and vascular and subcutaneous calcifications on both forearms after venous puncture on the right and extravasation of calcium gluconate during treatment on the left. The thrombosis and calcifications completely resolved following treatment with low-molecular-weight heparin and acetazolamide for 5 and 8 months, respectively.

CONCLUSIONS

This case represents the first PHP1A patient displaying thrombosis and the first successful use of acetazolamide for PHP1A-associated soft tissue calcifications, thus providing new insights into the treatment of non-endocrinological features in this disease.