Our son 4 months has been gaining weight rapidly currently weighs 20lbs we were referred by the health visitor to the doctor who referred us to the paediatrician as he was worried about weight gained and the size of his head. At the appointment yesterday we were shocked to discover they think he has PWS so blood test has been done but we just don't understand as he's so alert always smiling, babbling away starting to roll over on his own does anyone have any experience of this?