Three cases of multicentric carpotarsal osteolysis syndrome: a case series.

Background: Multicentric carpotarsal osteolysis syndrome (MCTO) is characterized by progressive destruction and disappearance of the carpal and tarsal bones associated with nephropathy. MCTO is caused by loss-of-function mutations in the MAF bZIP transcription factor B (MAFB) gene.

Case Presentation: This report describes three unrelated patients with MAFB mutations, including two male and one female patient. Osteolytic lesions in the carpal and tarsal bones were detected at 2 years, 12 years, and 14 months of age, respectively. Associated proteinuria was noted at 4 years, 12 years, and 3 months of age, respectively. Kidney biopsy was performed in two of them and revealed focal segmental glomerulosclerosis (FSGS). One patient showed progression to end-stage renal disease, that is by 1 year after the detection of proteinuria. The second patient had persistent proteinuria but maintained normal renal function. In the third patient, who did not undergo a kidney biopsy, the proteinuria disappeared spontaneously. The bony lesions worsened progressively in all three patients. Mutational study of MAFB revealed three different mutations, two novel mutations [c.183C > A (p.Ser61Arg) and c.211C > G (p.Pro71Ala)] and one known mutation [c.212C > T (p.Pro71Leu)].

Conclusion: We report three cases with MCTO and two novel MAFB mutations. The renal phenotypes were different among the three patients, whereas progressive worsening of the bony lesions was common in all patients. We also confirmed FSGS to be an early renal pathologic finding in two cases. A diagnosis of MCTO should be considered in patients with progressive bone loss concentrated primarily in the carpal and tarsal bones and kidney involvement, such as proteinuria.