Considering that inclusions of lipofuscin-like substances are observed in retinal pigmentary cells of patients with Stargardt's disease on the one hand, and that the early symptoms of neuronal ceroid lipofuscinosis (CLN3) are suggestive of Stargardt's disease on the other hand (age of loss of visual acuity, appearance of the fundus), we decided to test allelism of Stargardt's disease with the infantile (CLN1) and juvenile forms of neuronal ceroid lipofuscinosis (CLN3), which map to chromosomes 1p32 and 16p12-p11 respectively.
Recent advances in the genetics of NCL have enabled us to use polymorphic DNA markers linked to the CLN1 and CLN3 loci as a tool in the differential diagnosis of NCL.
The loci for the juvenile (CLN3) and infantile (CLN1) neuronal ceroid lipofuscinosis (NCL) types have been mapped by genetic linkage analysis to chromosome arms 16p and 1p, respectively.
The neuronal ceroid lipofuscinoses (NCL) are a relatively frequent group of progressive neurodegenerative disorders in children with similar, but not identical, clinical and morphological features, entailing different clinical groups, some of which have been found to represent different genetic entities, ie, infantile (INCL) or CLN1, late-infantile (LINCL) or CLN2, juvenile (JNCL) or CLN3, and a Finnish variant of LINCL or CLN5.
The main childhood subtypes are infantile (INCL;CLN1), classical late infantile (LINCL;CLN2) and juvenile NCL (JNCL;CLN3), distinguished on the basis of age of onset, clinical course and ultrastructural morphology, and recently genetic analysis.
A preliminary expression study of two of these mutant enzymes supports the conclusion that juvenile-onset NCL (JNCL with GROD) is caused by missense mutations in the PPT gene that result in mutated enzymes with residual PPT enzyme activity.
Mutations in the gene encoding a lysosomal enzyme, palmitoyl protein thioesterase (PPT), cause infantile NCL (locus CLN1 on chromosome 1p32) or Haltia-Santavuori disease.
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.
We determined that the mutations 223A --> G and 451C --> T in CLN1, T523-1G --> C, and 636 C --> T in CLN2, and deletion of a 1.02-kb genomic fragment in CLN3 are the five common mutations for NCL.
We have examined mRNA levels of the CLN1, CLN2, and CLN3 genes, which are associated with the infantile, late infantile, and juvenile forms of NCL in 64 different human tissues, and have grouped the results into gastrointestinal tract, central nervous system, glandular/secretory, muscle, and carcinoma tissue types. mRNA levels for CLN3 are highest in gastrointestinal tissue and are also high in glandular/secretory tissue, whereas mRNA levels for CLN1 and CLN2 do not appear to be preferentially elevated in any tissue type.
The infantile form of neuronal ceroid lipofuscinosis (INCL; CLN1) is the earliest onset form of the neuronal ceroid lipofuscinoses (NCL), a group of progressive encephalopathies of children.
In conclusion, the PPT1 expression pattern differed from the two other lysosomal enzymes implicated in NCL diseases, thus suggesting a distinctive role for PPT1 in brain development.
The NCLs include eight forms that result from genetic deficiency on genes CLN(1) to CLN(8), respectively: four classic forms with clinical onset at varying ages-infantile (INCL), late-infantile (LINCL), juvenile (JNCL), and adult (ANCL)-and four variants of late-infantile onset-the Finnish variant LINCL (fLINCL), Portuguese variant LINCL (pLINCL), Turkish variant LINCL (tLINCL), and progressive epilepsy with mental retardation (EPMR).
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).