Autosomal dominant hypoparathyroidism associated with short stature and premature osteoarthritis

Familial hypoparathyroidism is an unusual and genetically heterogeneous group of disorders that may be isolated or may be associated with congenital or acquired abnormalities in other organs or glands. We have evaluated a family with a novel syndrome of autosomal dominant hypoparathyroidism, short stature, and premature osteoarthritis. A 74-yr-old female (generation I) presented with hypoparathyroidism, a movement disorder secondary to ectopic calcification of the cerebellum and basal ganglia, and a history of knee and hip replacements for osteoarthritis. Two members of generation II and one member of generation III were also documented with hypoparathyroidism, short stature, and premature osteoarthritis evident as early as 11 yr. Because of the known association between autosomal dominant hypoparathyroidism and activating mutations of the calcium-sensing receptor (CaR) gene, further studies were performed. Sequencing of PCR-amplified genomic DNA revealed a leucine to valine substitution at position 616 in the first transmembrane domain of the CaR, which cosegregated with the disorder. However, this amino acid sequence change did not affect the total accumulation of inositol phosphates as a function of extracellular calcium concentrations in transfected HEK-293 cells. In conclusion, a sequence alteration in the coding region of the CaR gene was identified, but is not conclusively involved in the etiology of this novel syndrome. The cosegregation of hypoparathyroidism, short stature, and osteoarthritis in this kindred does suggest a genetic abnormality involving a common molecular mechanism in parathyroid, bone, and cartilage

Association between mutations in a thyroid hormone transporter and severe X-linked psychomotor retardation

Monocarboxylate transporter 8 (MCT8) is a thyroid hormone transporter, the gene of which is located on the X chromosome. We tested whether mutations in MCT8 cause severe psychomotor retardation and high serum triiodothyronine (T3) concentrations in five unrelated young boys. The coding sequence of MCT8 was analysed by PCR and direct sequencing of its six exons. In two patients, gene deletions of 2·4 kb and 24 kb were recorded and in three patients missense mutations Ala150Val, Arg171 stop, and Leu397Pro were identified. We suggest that this novel syndrome of X-linked psychomotor retardation is due to a defect in T3 entry into neurons through MCT8, resulting in impaired T3 action and metabolism

Functional analysis of monocarboxylate transporter 8 mutations identified in patients with X-linked psychomotor retardation and elevated serum triiodothyronine

Context: T-3 action in neurons is essential for brain development. Recent evidence indicates that monocarboxylate transporter 8 (MCT8) is important for neuronal T-3 uptake. Hemizygous mutations have been identified in the X-linked MCT8 gene in boys with severe psychomotor retardation and elevated serum T-3 levels. Objective: The objective of this study was to determine the functional consequences of MCT8 mutations regarding transport of T-3. Design: MCT8 function was studied in wild-type or mutant MCT8-transfected JEG3 cells by analyzing: 1) T-3 uptake, 2) T-3 metabolism in cells cotransfected with human type 3 deiodinase, 3) immunoblotting, and 4) immunocytochemistry. Results: The mutations identified in MCT8 comprise four deletions (24.5 kb, 2.4 kb, 14 bp, and 3 bp), three missense mutations (Ala224Val, Arg271His, and Leu471Pro), a nonsense mutation (Arg245stop), and a splice site mutation (94 amino acid deletion). All tested mutants were inactive in uptake and metabolism assays, except MCT8 Arg271His, which showed approximately 20% activity vs. wild-type MCT8. Conclusion: These findings support the hypothesis that the severe psychomotor retardation and elevated serum T-3 levels in these patients are caused by inactivation of the MCT8 transporter, preventing action and metabolism of T-3 in central neurons

The effects of palovarotene in patients with fibrodysplasia ossificans progressiva : a plain language summary

What is this summary about? This is a plain language summary of an article originally published in the Journal of Bone and Mineral Research. People with fibrodysplasia ossificans progressiva (FOP) become physically disabled over time as new bone forms in places where it is not usually found, such as in muscles and ligaments. Until recently, there were no treatments for FOP that had been proven through clinical trials; however, a drug called palovarotene has been tested in clinical trials and may be effective. Here, we describe the MOVE trial, which investigated how effectively palovarotene works, as well as its safety in treating patients with FOP. What were the results? Results from MOVE suggest that palovarotene may reduce extra bone formation outside the normal skeleton. Patients with FOP who took palovarotene formed less new bone than those who did not take palovarotene. The most common side effects involved the skin, and included dryness and irritation. Some children who were still growing when they took palovarotene had a side effect that resulted in the (normal) growth of their skeleton stopping too soon. What do the results of the trial mean? Palovarotene may be a useful treatment option for FOP. Patients, caregivers, and doctors would need to consider the benefits and risks of treatment with palovarotene, particularly with growing children.This is a plain language summary of an article originally published in the Journal of Bone and Mineral Research: Pignolo, R.J., Hsiao, E.C., Al Mukaddam, M., Baujat, G., Berglund, S.K., Brown, M.A., Cheung, A.M., De Cunto, C., Delai, P., Haga, N., Kannu, P., Keen, R., Le Quan Sang, K.-H., Mancilla, E.E., Marino, R., Strahs, A. and Kaplan, F.S. (2023), Reduction of New Heterotopic Ossification (HO) in the Open-Label, Phase 3 MOVE Trial of Palovarotene for Fibrodysplasia Ossificans Progressiva (FOP). J Bone Miner Res, 38: 381-394. https://doi.org/10.1002/jbmr.4762</p

Reduction of new heterotopic ossification (HO) in the open-label, phase 3 MOVE trial of palovarotene for fibrodysplasia ossificans progressiva (FOP)

Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare, severely disabling genetic disorder of progressive heterotopic ossification (HO). The single-arm, open-label, phase 3 MOVE trial (NCT03312634) assessed efficacy and safety of palovarotene, a selective retinoic acid receptor gamma agonist, in patients with FOP. Findings were compared with FOP natural history study (NHS; NCT02322255) participants untreated beyond standard of care. Patients aged ≥4 years received palovarotene once daily (chronic: 5 mg; flare-up: 20 mg for 4 weeks, then 10 mg for ≥8 weeks; weight-adjusted if skeletally immature). The primary endpoint was annualized change in new HO volume versus NHS participants (by low-dose whole-body computed tomography [WBCT]), analyzed using a Bayesian compound Poisson model (BcPM) with square-root transformation. Twelve-month interim analyses met futility criteria; dosing was paused. An independent Data Monitoring Committee recommended trial continuation. Post hoc 18-month interim analyses utilized BcPM with square-root transformation and HO data collapsed to equalize MOVE and NHS visit schedules, BcPM without transformation, and weighted linear mixed-effects (wLME) models, alongside prespecified analysis. Safety was assessed throughout. Eighteen-month interim analyses included 97 MOVE and 101 NHS individuals with post-baseline WBCT. BcPM analyses without transformation showed 99.4% probability of any reduction in new HO with palovarotene versus NHS participants (with transformation: 65.4%). Mean annualized new HO volume was 60% lower in MOVE versus the NHS. wLME results were similar (54% reduction fitted; nominal p = 0.039). All palovarotene-treated patients reported ≥1 adverse event (AE); 97.0% reported ≥1 retinoid-associated AE; 29.3% reported ≥1 serious AE, including premature physeal closure (PPC)/epiphyseal disorder in 21/57 (36.8%) patients aged &lt;14 years. Post hoc computational analyses using WBCT showed decreased vertebral bone mineral density, content, and strength, and increased vertebral fracture risk in palovarotene-treated patients. Thus, post hoc analyses showed evidence for efficacy of palovarotene in reducing new HO in FOP, but high risk of PPC in skeletally immature patients