Lysinuric protein intolerance presenting with recurrent infections, severe liver injury and anemia in the neonatal period: A case report with organic acidemia-like manifestations

Background Lysine uric protein intolerance (LPI) is a rare autosomal recessive genetic metabolic disorder caused by variations in the SLC7A7 gene. The typical manifestations are protein intolerance, growth retardation and hyperammonemia. Case Report A 2-month-old male infant presented with recurrent respiratory tract infections. Upon admission, anemia and significantly elevated levels of liver enzymes and lactate dehydrogenase were identified. Metabolic screening indicated hyperammonemia. Blood tandem mass spectrometry revealed elevated acetylcarnitine (C2) and propionylcarnitine (C3), raising the possibility of methylmalonic acidemia (MMA) or propionic acidemia (PA). Further analysis of urine organic acids demonstrated increased concentrations of glutaric acid, 2-hydroxyglutaric acid, and 2-ketoglutaric acid. The physical examination indicated an anemic appearance and hepatomegaly, while growth and developmental parameters remained within normal limits. The response to conventional liver protection, iron supplementation, and other supportive treatments was unsatisfactory. Final gene mutation analysis via whole exome sequencing revealed a compound heterozygous variation in the SLC7A7 gene, thereby confirming the diagnosis of lysine uric acid protein intolerance. Conclusion This article presents a case of an infant with LPI exhibiting atypical clinical manifestations. The onset was marked by recurrent respiratory tract infections, markedly elevated liver enzymes and lactate dehydrogenase levels, as well as anaemia. Tandem mass spectrometry indicates a potential diagnosis of methylmalonic acidemia. The objective is to investigate these atypical manifestations and underscore the necessity for vigilance regarding cross-interference in tandem mass spectrometry, thereby emphasising the critical importance of early genetic diagnosis of atypical metabolic disorders during infancy.