Jelte de Haan, a five-year-old boy from Leeuwarden, Netherlands, has died after a battle with metachromatic leukodystrophy (MLD), a rare and fatal neurological disease. Jelte became a public figure advocating for research into metabolic diseases, notably through involvement with the Serious Request fundraising campaign which raised over 11 million euros. His family shared the news of his peaceful passing on social media, expressing both sadness and acceptance. They had been celebrating monthly “fun days” knowing his life would be short, and actively fundraising for Metakids, a foundation dedicated to research. Jelte’s efforts contributed significantly to raising awareness and funds for metabolic disease research, which is the leading cause of death among children. A new award, the Jelte NextGen Award, has been created in his name to recognize young scientists working on treatments for these conditions. He “retired” from public appearances on his fifth birthday.