BackgroundHyaline fibromatosis syndrome is a rare progressive autosomal recessive connective tissue disorder caused by a mutation in theANTXR2/CMG2gene. According to its severity, patients may present with skin nodules or visceral infiltration, which carries a poor prognosis. Hypercalcemia has not been reported as a presenting feature of this syndrome. Stimulation of osteoclasts by inflammatory factors and immobilization­-induced hypercalcemia have played role in the pathophysiology. To our knowledge, this is the first report of hypercalcemia-associated hyaline fibromatosis syndrome.Case presentationHere, we describe cases of two Sudanese patients, a boy aged 9 months and a girl aged 3.5 years with hypercalcemia as an associated presenting feature of hyaline fibromatosis syndrome. Other features include gingival hypertrophy, painful joint swellings, and restriction of movement, which was misdiagnosed as juvenile rheumatoid arthritis. Workup showed normal phosphate, normal to mildly elevated parathyroid hormone, low vitamin D 25. Genetic testing confirmed the mutation of theANTXR2/CMG2gene. Both patients responded well to medical therapy for hypercalcemia, but one of them with the severe form of juvenile hyaline fibromatosis died due to sepsis, while the other one has maintained normocalcemic status.ConclusionsThese cases highlight the rare presentation of this syndrome and reflect the importance of biopsy and genetic testing in reaching the diagnosis, especially when the clinical presentation can mimic other inflammatory bone disorders. Calcium levels should be checked in such cases.