TPP1 and glycogen storage disease VI: Subunit C of mitochondrial ATP synthase (SCMAS), which has been previously detected in urine from NCL patients (Wisniewski et al., 1994, 1995), was present in four out of the five CSF samples from CLN2 disease patients (Sleat et al., 2017), suggesting that it is a biomarker for CLN2 disease.