Proximal tibiofibular synostosis with 49,XXXXY syndrome, a rare congenital bone anomaly

Abstract

The 49,XXXXY syndrome was fi rst reported in 1960 by Fraccaro et al. This rare sex chromosome aneuploidy syndrome has an approximate incidence of 1 in 85 000 male births. Clinical features of this syndrome include mental retardation, characteristic facies, skeletal malformations (particularly affecting the forearms), and genital hypoplasia. Congenital heart defects are a less commonly associated abnormality. The 49,XXXXY syndrome is often referred to as “Klinefelter variant.” However, some reports make a point of differentiating this sex chromosome aneuploidy from Klinefelter syndrome. A 49,XXXXY karotype is thought to arise from maternal nondisjunction during meiosis I and II. Such successive nondisjunctions theoretically produce an egg with four X chromosomes, resulting in an embryo with 49,XXXXY after fertilization by a Y-bearing sperm. In patients with the 49,XXXXY syndrome, bone deformities are found in some epiphyses. This syndrome emphasizes the “classic triad” of mental retardation, radioulnar synostosis, and hypogonadism. Although radioulnar synostosis is not an uncommon anomaly in the upper limb, the counterpart in the lower limb, proximal tibiofi bular synostosis, is exceedingly rare. We report herein the case of a 28-year-old man with no radioulnar synostosis but with proximal tibiofi bular synostosis. We suggest that nonseparation of the proximal ends of the tibial and fi bular shaft represents the same error of segmentation as radioulnar synostosis. To the best of our knowledge, proximal tibiofi bular synostosis with 49,XXXXY syndrome has not been reported previously. Case report