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49, XXXXY syndrome is one of the rarest sexual chromosome disorders, with an incidence of 1:85000–100000 males. It is caused by nondisjunction of the X chromosomes in both meiosis I and II. Early intervention is vital to improve behavioural, neural and sexual well‐being. Information about sexual and developmental aspects is extremely limited in previous literature. We present a case of a 26‐month‐old male child presenting with hypotonia, micropenis and bilateral cryptorchidism. Karyotype study was done in Jordan at the age of 16 months and revealed 49, XXXXY syndrome. Global developmental delay, hypotonia and weak truncal muscles were noted on examination. Growth parameters were within normal limits. Kidney ultrasound revealed findings suggestive of Vesicoureteral reflux. Laboratory investigations revealed hypoandrogenism with normal 17‐OHP levels. This study reviews current knowledge about sexual and developmental characteristics of 49, XXXXY syndrome. [ABSTRACT FROM AUTHOR]

Sex chromosome tetrasomy and pentasomy conditions occur in 1:18 000-1:100 000 male births. While often compared with 47,XXY/Klinefelter syndrome because of shared features including tall stature and hypergonadotropic hypogonadism, 48,XXYY, 48,XXXY and 49,XXXXY syndromes are associated with additional physical findings, congenital malformations, medical problems and psychological features. While the spectrum of cognitive abilities extends much higher than originally described, developmental delays, cognitive impairments and behavioural disorders are common and require strong treatment plans. Future research should focus on genotype-phenotype relationships and the development of evidence-based treatments. The more complex physical, medical and psychological phenotypes of 48,XXYY, 48,XXXY and 49,XXXXY syndromes make distinction from 47,XXY important; however, all of these conditions share features of hypergonadotropic hypogonadism and the need for increased awareness, biomedical research and the development of evidence-based treatments. [ABSTRACT FROM AUTHOR]