Lysinuric Protein Intolerance: A Treatable Cause of Developmental Delay with Multiple Complications

Background: Lysinuric protein intolerance (LPI) is a multi systemic disease with a variety of clinical symptoms. Early and aggressive treatment can significantly reduce the number of hyperammonaemic episodes and prevent mental disability. Case series: We report a case series from two siblings with LPI: The eldest boy presented at three and a half years of age with short stature, global developmental delay & a history of recurrent infections. His younger brother was identified in the newborn period with lethargy and weight loss. Basic metabolic screening showed hyperammonaemia, gross urinary excretion of lysine & to a lesser degree increased excretion of arginine, ornithine and orotic acid. Plasma amino acids showed either low or low normal lysine, arginine and ornithine. Results: Both cases were treated with protein restriction, nitrogen scavengers, citrulline and L-carnitine. They were provided with an appropriate oral and intravenous emergency regimen for use when unwell. At the last follow-up the eldest boy showed a marked improvement in his development, whilst the youngest infant has normal physical & mental development for age. Conclusions: Marked improvement in LPI patients can be achieved by strict diet and medication with early identification & treatment likely to lead to the best possible intellectual outcomes.