CLN5 is a lysosomal bis(monoacylglycero)phosphate (BMP) synthase essential for lysosomal function and neuronal health 1. The protein catalyzes BMP synthesis through an energy-independent base exchange reaction between two lysophosphatidylglycerol molecules, with increased activity on BMP-laden vesicles 1. BMP is a critical phospholipid constituent of late endosomes/lysosomes that stimulates lipid catabolism, cholesterol homeostasis, and lysosomal organization 1. CLN5 deficiency causes variant late-infantile neuronal ceroid lipofuscinosis (Batten disease), with disease onset between 4-7 years, characterized by progressive neuronal loss, visual failure, motor and mental decline, epilepsy, and premature death 23. Loss of CLN5 function leads to massive accumulation of its precursor lysophosphatidylglycerol, BMP depletion, and dysfunctional lipid metabolism 1. Recent evidence reveals that CLN5 deficiency impairs glucose uptake and calcium homeostasis, with PHGDH identified as a potential biomarker 4. Genetically, CLN5 is implicated in Alzheimer's disease pathogenesis through lysosomal dysfunction pathways 5. Gene therapy approaches using adeno-associated viral vectors encoding CLN5 show promise in preclinical models, slowing disease progression and preserving visual and neurological function 6.