Rare diseases, defined by the 2002 Rare Disease Act, affect fewer than 5 in 10,000 individuals. Rare metabolic bone diseases (MBDs), such as osteogenesis imperfecta, hypophosphatasia, osteopetrosis, and other unclassified disorders, can disrupt bone development and remodeling, posing diagnostic and management challenges. This study analyzed data from the rarembd.in registry (2010-2024), a 15-year database documenting only rare MBDs. Clinical presentation and demographic data of patients with rare MBDs were collated. Common MBDs (osteoporosis, primary hyperparathyroidism) were excluded. Genetic testing was performed in a subset of patients. There was a total of 218 patients with an almost equal gender distribution (male-to-female ratio of 1:1.07) and a mean age of 29.1 ± 18.9 years. The registry identified 29 rare MBDs with three main disease categories: demineralization disorders (50.4%), disorders of bone matrix and cartilage formation (32.5%), and sclerotic disorders (13.7%); with a smaller proportion categorized as unclassified bone disorders (2.7%). Rickets/osteomalacia (27.1%) was the most common, followed by osteogenesis imperfecta (23.4%) and fibrous dysplasia/McCune-Albright syndrome (18.8%). Fractures affected 57.7% of patients, with 24.5% experiencing multiple fractures, while 31.1% exhibited skeletal deformities. Mutation analysis in our registry identified pathogenic variants in the SOST, TGFβ1, SLC34A3, ALPL, and VCP genes, confirming the genetic basis of sclerosteosis, Camurati-Engelmann disease, hypophosphatemic rickets, hypophosphatasia, and IBMPFD, respectively. Different management strategies were used that included teriparatide, bisphosphonates (zoledronate or alendronate) with total contact casting, intralesional zoledronate, denosumab, calcium, active vitamin D, and recombinant human growth hormone. Total parathyroidectomy was performed in specific cases. The registry classified RMBDs into four categories, with demineralization disorders being the most common, followed by bone matrix/cartilage formation disorders, sclerotic diseases, and unclassified cases. There were 29 RMBDs, and rickets/osteomalacia was the most prevalent subtype, tumor-induced osteomalacia followed by familial hypophosphatemic osteomalacia. Among the unclassified bone disorders, fragility fractures emerged as the most common presentation.

Camurati-Engelmann disease (CED) is an extremely rare autosomal dominant bone dysplasia characterized by hyperostosis of the long bones and, in severe cases, of the skull and axial skeleton. This study aims to analyze the impact on quality of life in a non-selected group of CED patients. This monocentric case series study included 15 patients who completed a survey that collected demographic characteristics, disease-related information and a validated SF-12 questionnaire to assess quality of life. Physical (PCS-12) and Mental (MCS-12) Component Summary scores were compared with the mean SF-12 scores of the U.S. reference population. Patients had significantly lower PCS-12 score [29.8 (7.5)] compared to the reference population [50.0 (10.0)] (p<0.0001). However, there were no differences in the MCS-12 score [48.8 (11.23) vs 50.0 (10.0)]. The most reported symptoms were fatigue (100%), pain in the limbs (93.3%) and muscle pain (86.7%). CED patients have significantly lower physical quality of life than the general population, due to the high prevalence of physically limiting problems. However, mental health appears unaffected.

Camurati-Engelmann disease, type 1 (CED1, OMIM # 131300) is the rare autosomal dominant skeletal dysplasia caused by select heterozygous loss-of-function defects within the gene TGFB1, which encodes transforming growth factor beta 1 (TGFB1). CED1 mutations are found in TGFB1 exons 1-4 that form the latency-associated peptide (LAP) of pro-TGFB1. Consequently, skeletal action of TGFB1 increases and thereby enhances bone formation manifest clinically as "progressive diaphyseal dysplasia". Beginning 24 years ago negative TGFB1 analysis suggested rare genetic heterogeneity for CED, and Online Mendelian Inheritance In Man designated, of unknown etiology, "CED2" (OMIM % 606631). In 2024, three sporadic occurrences considered CED2 were reported to harbor either of two mutations of TGFB2, which encodes the LAP of transforming growth factor beta 2 (TGFB2). Herein, three adults (father, son, daughter) having the CED2 phenotype in a Peruvian family revealed a novel missense variant (c.108G > T, p.R36S) within the TGFB2 LAP domain. Debilitating painful skeletal disease featuring hyperostosis of entire long bones, worse in the men, presented early in childhood. Aminobisphosphonate therapy seemed helpful. Their TGFB2 variant was within a highly conserved domain across species, absent in the gnomAD database, "possibly damaging" by Polyphen-2, not tolerated by SIFT, homologous with TGFB1 at the same amino acid position (R36) as one reported TGFB2 mutation, co-segregated as autosomal dominant, and "likely pathogenic" per ACMG guidelines.

Osteosclerotic bone diseases include more than 30 rare diseases characterized by excessive bone formation. The aim of this study is to compare the molecular pathogenesis and prognostic features of 12 different osteosclerotic diseases. Thirty-four patients from 23 families were included, 25 of whom were followed for a period of one to 22 years. Exome sequencing was performed in 20 families. Primary hypertrophic osteoarthropathy (PHOAR1/2) was found in 12 patients, followed by juvenile Paget's disease (JPD)-5 in five, craniometaphyseal dysplasia (CMD) and Camurati-Engelmann disease (CED) in four, Ghosal hematodiaphyseal dysplasia (GHDD) in three patients, sclerosteosis-1 in two patients, and ultra-rare diseases including trichothiodystrophy-1, prenatal Caffey disease, melorheosteosis, and Lenz-Majewski hyperostotic dwarfism in one patient each. Patients with CMD and sclerosteosis-1 had severe cranial sclerosis leading to facial dysmorphism. CMD was characterized by metaphyseal widening, radiolucency, and diaphyseal sclerosis of the long bones in early childhood and later developed Erlenmeyer flask deformity sparing the vertebrae and pelvis, whereas sclerosteosis-1 manifested as generalized sclerosis. CED and GHDD share bone pain, difficulty in walking, and diaphyseal sclerosis, with some patients also having bone marrow involvement. Interestingly, patients with CED and JPD-5 showed osteopenia in early childhood, followed by the development of osteosclerosis in late childhood. Clinical and radiologic findings improved over time in PHOAR1 patients, whereas they progressed in JPD-5 and trichothiodystrophy-1 patients. Intra- and interfamilial clinical differences were observed in CMD, CED, JPD-5, and GHDD. The knowledge gained about the natural history of osteosclerotic diseases will make an important contribution to their diagnosis and management.