title: Tetrasomy and pentasomy of the X chromosome.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors: Stedelijk Ziekenhuis, Brugsesteenweg 90, 8800 Roeselare, Belgium. eschoubben@yahoo.com
authors: Edith
authors: E
authors: Schoubben
authors: Karin
authors: K
authors: Decaestecker
authors: Koen
authors: K
authors: Quaegebeur
authors: Lode
authors: L
authors: Danneels
authors: Geert
authors: G
authors: Mortier
authors: Luc
authors: L
authors: Cornette
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