When Dark Urine Is Not Nephritis: A Life-Threatening Case of Lipin-1 Deficiency in Infancy.

Lipin-1 deficiency is a rare inherited metabolic disorder and a major genetic cause of severe, recurrent rhabdomyolysis in early childhood, carrying a significant risk of acute kidney injury and mortality if unrecognized. We report the case of a male toddler who first presented at 19 months of age with dark urine and intercurrent viral illness. Initial investigations demonstrated hematuria/myoglobinuria, proteinuria, and markedly elevated transaminases, leading to a presumptive diagnosis of glomerulonephritis. Creatine kinase (CK) was not measured at that time, and the episode was retrospectively felt to represent missed rhabdomyolysis. The patient subsequently presented similarly with abdominal pain and dark urine when profound rhabdomyolysis was identified by checking CK (CK >120,000 U/L). Aggressive hyperhydration led to biochemical improvement, and genetic testing confirmed a homozygous pathogenic LPIN1 exon 18 deletion. Since diagnosis, he has experienced multiple recurrent episodes of rhabdomyolysis, predominantly triggered by viral infections, requiring repeated admissions and intensive metabolic management. Notably, this patient also has a background of global developmental delay (GDD). To our knowledge, this represents the first reported case describing an association between LPIN1 deficiency and developmental delay. Emerging experimental and clinical evidence suggests a potential biological link between LPIN1 dysfunction, impaired myelination, and abnormal neurodevelopment, raising the possibility that developmental delay may be an under-recognized phenotypic feature of this condition. This case highlights the importance of considering rhabdomyolysis in children presenting with dark urine and intercurrent illness and the critical role of early CK measurement in preventing missed diagnoses. Prompt recognition of LPIN1 deficiency is essential, as delayed treatment may result in life-threatening complications and avoidable morbidity.