My son was born with severe hydronephrosis.nicu 4 days.failure to thrive first 2 years.age 4 now.chronic constipaton.no bm for 4days.what could be?

Has he had a CMA?: A chromosomal microarray ; genetics eval. Look for genetic syndromes ( some hereditary) associated with congenital hydronephrosis ; inadequate weight gain. Low muscle tone can cause chronic constipation along with motor delays. Constipation should be treated with a "clean-out" followed by MiraLAX (polyethylene glycol) for at least 6 mos., diet changes ; bowel re-training per his pediatrician or pediatric gi.

Workup and Mgt: As your son's kidneys grow with time the effect of the initial kidney disease may be less, but I would suggest following his renal function with blood and urine tests. In addition, a comprehensive metabolic panel, CBC, Thyroid screening and CF sweat tests are indicated. Diet changes to include fiber and drinking water will help in his management.