A unique association of Noonan syndrome and 47,XYY syndrome in a male presenting with failure to thrive

We describe a 24-month-old male patient who presented to our Genetics-Endocrinology Clinic with a history of failure to thrive, short stature and cryptorchidism. Soon after birth he was diagnosed with 47,XYY syndrome, but due unusual facial features had further diagnostic workup which revealed Noonan syndrome (NS) as well. This report illustrates significant phenotypic–cytogenetic variability within the clinical presentation of NS and 47,XYY syndrome, as well as the need to investigate patients for other genetic defects when phenotype does not correlate with genotype. Furthermore, in this case, the cellular pathways attenuating growth via PTPN11 mutation appear to supersede the SHOX overdosage—an observation that can lead to further research in genetic mechanisms of growth physiology.