World Homocystinurias Awareness Day, also known as World HCU Awareness Day, is observed worldwide every May 18. This day was established to educate the public about homocystinurias, a group of inherited metabolic disorders that disrupt the metabolism of the essential amino acid methionine, leading to the accumulation of homocysteine in the body. The event highlights the various forms of homocystinuria, primarily caused by enzyme deficiencies, and the significant health impacts these disorders have on individuals, including brain, eye, blood, and skeletal issues. Organizations involved in this observance aim to raise global awareness of the condition and its effects on patients and their families. People can participate by learning about homocystinurias, sharing information, donating to relevant organizations, and using social media hashtags like #WorldHomocystinuriasAwarenessDay, #WHAD, and #GoBlue4HCU.