Nonsense mutations in CLN1 account for 52.3% of all disease causing alleles in infantile NCL, the most common of which worldwide is the p.R151X mutation.
The lysosomal storage of lipofuscins is the common pathological feature that characterizes the infantile, late-infantile, juvenile (Batten's disease), and Finnish-variant neuronal ceroid lipofuscinosis (INCL, LINCL, JNCL and FNCL), which are due to mutations in the genes CLN1, CLN2, CLN3, and CLN5, respectively.
Infantile-onset NCL (CLN1 disease) is caused by severe deficiency in a soluble lysosomal enzyme, palmitoyl-protein thioesterase-1 (PPT1) and no therapy beyond supportive care is available.
In five of the eight NCL variants distinguished at present, genes associated with the disease process have been isolated and characterized (CLN1, CLN2, CLN3, CLN5, CLN8).
The NCLs are clinically and genetically heterogeneous and more than 14 genetically distinct NCL subtypes have been described to date (CLN1-CLN14) (Haltia and Goebel, 2012 [1]).
Cases of ceroid lipofuscinosis with cytoplasmic storage of granular osmiophilic deposits are associated with reduced activity of palmitoyl-protein thioesterase-1 (PPT-1) and mutations in CLN1, and occur from infancy to adulthood.
In neutral conditions, pH 6.0, the PPT1 enzyme activities in NCL 1 patients showed rather higher residual activities and intermediate activities in heterozygotes in NCL 1, which was probably caused by mutated proteins in three cases with NCL 1 patients.
Neuronal ceroid lipofuscinoses (NCL) comprise the most common group of childhood encephalopathies caused by mutations in eight genetic loci, CLN1-CLN8.