Ceroid lipofuscinosis, neuronal, 5 (CLN5) was originally described as the 'Finnish variant of late-infantile NCL' (Finnish vLINCL). With the identification of molecular defect, CLN5 now refers to CLN caused by mutation in the CLN5 gene, regardless of the age at onset. Typical CLN5, Finnish vLINCL form, first presents at the age of 4 to 7 years usually with motor clumsiness and progressive mental deterioration. Visual failure and myoclonic seizures appear later. Most patients become non-ambulatory during the second decade with death between 13 and 30 years of age. MRI studies show signs of cortical atrophy. Three atypical phenotypes can also be recognized: juvenile, adult and infantile CLN5 disease. The product of CLN5 gene is a soluble lysosomal glycoprotein, but the pathogenetic mechanisms leading to neuronal death and accumulation of cytosomes with curvilear profiles, and/or fingerprint profiles are mostly unknown. The accumulating substance is subunit c of mitochondrial ATP synthase. See review: Kousi et al. Human mutation 2011:33:42-63