Henry had Rett syndrome.

NBC News Chief Foreign Correspondent Richard Engel has announced the death of his 6-year-old son Henry. The heartbroken father announced his son's death in a moving post on Twitter. His son Henry Engel was diagnosed with Rett syndrome after his parents noticed he wasn't reaching his milestones. Henry, who was born on September 29th, 2015, had a mutation in his MECP2 gene. The MECP2 mutations cause Rett syndrome, a disorder that typically affects girls after their first birthday. The disorder prevents children from learning skills. It also causes cognitive deficits, loss of speech, and numerous motor difficulties. Alongside a photo of his son, Richard shared the devastating news: "Our beloved son Henry passed away. He had the softest blue eyes, an easy smile, and a contagious giggle. "We always surrounded him with love and he returned it, and so much more. Mary and Richard." https://twitter.com/RichardEngel/status/1560272477854478343 His parents also shared that researchers are making amazing progress using Henry’s cells to help cure RETT Syndrome. They don't want "others to endure this terrible disease". The team at Texas Children’s Hospital’s Duncan Neurological Research Institute has been studying Henry since 2018. "Henry’s mutation has been studied by Dr. Huda Zoghbi, who discovered that MECP2 mutations cause Rett syndrome." "Henry made the best of every single day and worked tirelessly in his many physical and developmental therapies. "He continues to be an inspiration for Dr. Zoghbi and her team as they work to find effective treatments for Rett syndrome, and they already are making significant progress with Henry’s own cells." Dr. Huda Zoghbi said: "We will continue to push as hard as possible to develop treatments. This is how we will honor his life.” Henry's parents have asked the public to honour him by donating to research efforts here.