The Key to the Fountain of Youth? TLC Explores Medical Mystery in "40 YEAR OLD CHILD: A NEW CASE" - Monday, August 19 at 10 PM (ET/PT)

In an all-new one-hour special, 40 YEAR OLD CHILD: A NEW CASE, TLC revisits the Williams family in Billings, Montana, whose 8-year-old daughter Gabby suffers a mystery medical condition that slows her rate of aging. The Williams along with a handful of other families are facing the unknown when battling against this bizarre and inexplicable syndrome that affects the growth and overall development of their children, from blindness and deafness to the inability to walk, eat or even speak on their own. Following the everyday lives of these families and the doctors who have dedicated their careers to studying the signs of aging and are determined to find an answer, 40 YEAR OLD CHILD: A NEW CASE premieres Monday, August 19 at 10 PM (ET/PT) on TLC.

Two years ago, the Williams family embarked on a journey to discover why their daughter Gabby wasn't growing. But cutting edge medical testing failed to provide a diagnosis. Now, two new cases have emerged: a 29-year-old Florida man with the body of a 10-year-old, and a 31-year-old Brazilian woman who's still the size of a toddler. Can these incredible people help doctors solve this mystery? And will a voyage across America finally lead Gabby's family to some answers?

40 YEAR OLD CHILD: A NEW CASE

One-Hour Special Premieres Monday, August 19 at 10 PM (ET/PT)

Gabby is eight years old but is still a baby. She suffers from a mystery medical condition that slows her rate of aging. Two years ago, her family embarked on a journey to discover the cause. But cutting edge medical testing failed to provide a diagnosis. Now, two new cases have emerged: A 29-year-old Florida man with the body of a 10-year-old, and a 31-year-old Brazilian woman who's still a toddler. Can these incredible people help doctors solve this mystery? And will a voyage across America finally lead Gabby's family to some answers?