Bloom syndrome

A 5-year-old boy is brought to a dermatologist by his mother for evaluation of persistent facial redness for the past 2 months. The redness started over his nose and cheeks when he went to a summer camp where he was outdoors most of the day. The mother states that her son has always been sensitive to the sun, but has never had this type of redness before. Physical examination shows spidery veins and redness of the face in a butterfly distribution. Closer examination shows a long drawn face with protruding ears, and the patient appears quite small for his age. The mother mentions that he was born small and has had significant trouble meeting appropriate milestones in terms of growth. What chromosome is likely to be affected given this patient's presentation?