Welcome to our research highlight on classical homocystinuria (HCU), presented by Metabolic Support, HCU Network America, CanPKU+, and RARE-X.

Classical HCU is a rare inherited metabolic disorder caused by cystathionine beta-synthase deficiency, which leads to elevated homocysteine levels and systemic complications. Beyond physical health, affected individuals frequently face significant behavioural and neuropsychiatric challenges—including anxiety, depression, mood disturbances, and cognitive difficulties—that heavily impact daily functioning and long-term outcomes.

Because these behavioural symptoms can easily be underrecognised in routine clinical settings, capturing real-world patient and carer experiences is essential. Drawing on patient-reported data from the RARE-X platform, this study characterises the prevalence and onset of behavioural manifestations in classical HCU, highlighting that over half of respondents experience mental health or behavioural conditions and underscoring the vital need for routine behavioural monitoring alongside metabolic management.

The poster below summarises the key findings of this study: