IMPE Abstracts

Background: Multicentric carpotarsal osteolysis syndrome (MCTO) is a rare skeletal disorder commonly caused by MAFB gene mutation. It is characterized by aggressive carpo tarsal osteolysis frequently associated with progressive nephropathy. MAFB negative regulates receptor activator of nuclear factor κB ligand - (RANKL) mediated osteoclast differentiation.

Problem: The diagnosis and treatment of MCTO represents a challenge and many patients are diagnosed with Juvenile Idiopathic Artrithis (JIA) before. We describe a patient with a multicentric carpotarsal osteolysis without nephropathy.

Clinical management: A two year old girl developed edema in hands, wrists and ankles, with limited movement that affected her walk. Physical examination revealed height in the 10-25^th percentile, weight in 10^th percentile, and subtle facial dysmorphism (maxillary hypoplasia, obliterated nasogenian folds, smooth philtrum, small mouth, high arched palate and micrognathia). She had mild pectus excavatum, swollen hands and ankles, difficulty standing, varus rigid right foot, muscular hypotrophy in lower limbs. Palpation and passive mobility were painful. Hands radiography revealed absence of ossification nuclei in the carpus and osteolytic lesions at the proximal end of the metacarpal. Feet Rx showed alteration in morphology and density of the tarsal bones, metatarsal with varus deviation. Laboratory tests revealed normal serum creatinine, albumin, urea, erythrocyte sedimentation rate, C-reactive protein and no proteinuria in 24 hs urine test. A genetic test was done. The variant c.176C>T was detected in exon 1 of the MAFB gene coding for the p.(Pro59Leu) change in heterozygosis. This variant was not present in the parents, indicating a de novo variant in the patient. The genetic study confirmed the diagnosis of MCTO and denosumab treatment was prescribed, which will be infused with hospitalization and strict controls. She will be the first young girl in the country whom this therapy will be used.

Discussion: MCTO can mimic JIA resulting in a delayed diagnosis. So, knowledge of its pathophysiology and access to molecular genetic testing, allowed us to detect this disease in an earlier stage, which permitted us to make better treatment choices and to offer genetic counseling to the family. The start of an anti-RANKL drug such as denosumab could improve the outcome for this pathology.