The challenges of pregnancy management in pyridoxine nonresponsive homocystinuria: The Irish experience

Many patients with inborn errors of metabolism, due to early diagnosis and improved management, are living longer with less disease burden. Several are now having families of their own. This poses challenges both for the metabolic control of the mother and potential secondary effects on the fetus, as well as the risk of inheriting the inborn error. Classical homocystinuria (HCU, OMIM 236200) is a rare multisystem condition with intellectual, skeletal, ocular, and thromboembolic complications. Ireland has included HCU in the National Newborn Bloodspot Screening Program since 1971. The European network and registry for homocystinurias and methylation defects (E-HOD) guidelines outline the requirements for management and monitoring of this condition and associated complications. Pregnancy alone has many potential complications. When combined with an underlying condition such as HCU, which is prothrombotic and requires a highly medicalized diet, there are significantly increased risks to both mother and baby. Colleagues previously published an Irish case of maternal HCU with successful pregnancy outcome. We add five pregnancies to two women with classical HCU to the literature. We use these to highlight the importance of careful metabolic control and managing the predictable HCU associated risks during pregnancy and the postpartum period. Our cases demonstrate the potential for healthy pregnancies in HCU and that this is best achieved with a motivated clinical team and good patient engagement. Only small numbers of pregnancies in HCU have been reported and we are still learning best practice, but proactive management is essential, as in any inborn error of metabolism.