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Tetrasomy and pentasomy of the X chromosome

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We describe a newborn girl with a life-threatening laryngomalacia and extreme hypotonia. Genetic analysis revealed the very rare genetic condition mosaicism of 48,XXXX and 49,XXXXX (50/50). We here state that the degree of early hypotonia constitutes an important early prognostic feature in this syndrome. The timely insertion of a gastrostomy is warranted in order to prevent aspiration. Conclusion: A karyotype is mandatory in female newborns with moderate to severe hypotonia in order to exclude polyploid mosaicism of the X chromosome. An ‘overall prognosis’ for 48,XXXX and 49,XXXXX girls is difficult to provide towards parents in line with a well-known, substantial variability in outcome for all polysomy X infants.

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Correspondence to Edith Schoubben.

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Schoubben, E., Decaestecker, K., Quaegebeur, K. et al. Tetrasomy and pentasomy of the X chromosome. Eur J Pediatr 170, 1325–1327 (2011).

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