Mutations in CLN7/MFSD8 are a common cause of variant late-infantile neuronal ceroid lipofuscinosis
Folkhälsan Institute of Genetics, Department of Medical Genetics and Neuroscience Center, University of Helsinki, Finland. Brain
(Impact Factor: 9.2).
02/2009; 132(Pt 3):810-9. DOI: 10.1093/brain/awn366
The neuronal ceroid lipofuscinoses (NCLs), the most common neurodegenerative disorders of childhood, are characterized by the accumulation of autofluorescent storage material mainly in neurons. Although clinically rather uniform, variant late-infantile onset NCL (vLINCL) is genetically heterogeneous with four major underlying genes identified so far. We evaluated the genetic background underlying vLINCL in 119 patients, and specifically analysed the recently reported CLN7/MFSD8 gene for mutations in 80 patients. Clinical data were collected from the CLN7/MFSD8 mutation positive patients. Eight novel CLN7/MFSD8 mutations and seven novel mutations in the CLN1/PPT1, CLN2/TPP1, CLN5, CLN6 and CLN8 genes were identified in patients of various ethnic origins. A significant group of Roma patients originating from the former Czechoslovakia was shown to bear the c.881C>A (p.Thr294Lys) mutation in CLN7/MFSD8, possibly due to a founder effect. With one exception, the CLN7/MFSD8 mutation positive patients present a phenotype indistinguishable from the other vLINCL forms. In one patient with an in-frame amino acid substitution mutation in CLN7/MFSD8, the disease onset was later and the disease course less aggressive than in variant late-infantile NCL. Our findings raise the total number of CLN7/MFSD8 mutations to 14 with the majority of families having private mutations. Our study confirms that CLN7/MFSD8 defects are not restricted to the Turkish population, as initially anticipated, but are a relatively common cause of NCL in different populations. CLN7/MFSD8 should be considered a diagnostic alternative not only in variant late-infantile but also later onset NCL forms with a more protracted disease course. A significant number of NCL patients in Turkey exist, in which the underlying genetic defect remains to be determined.
Available from: Romina Kohan
- "FP, n = 2 E3, p.Arg35*   I2, c.63-4delC  E10, p.Thr294Lys   E13, p.Arg482*  "
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ABSTRACT: The Argentinean program was initiated more than a decade ago as the first experience of systematic translational research focused on NCL in Latin America. The aim was to overcome misdiagnoses and underdiagnoses in the region.
216 NCL suspected individuals from 8 different countries and their direct family members.
Clinical assessment, enzyme testing, electron microscopy, DNA screening.
1) The study confirmed NCL disease in 122 subjects. Phenotypic studies comprised epileptic seizures and movement disorders, ophthalmology, neurophysiology, image analysis, rating scales, enzyme testing, and electron microscopy, carried out under a consensus algorithm; 2) DNA screening and validation of mutations in genes PPT1 (CLN1), TPP1 (CLN2), CLN3, CLN5, CLN6, MFSD8 (CLN7), and CLN8: characterization of variant types, novel/known mutations and polymorphisms; 3) Progress of the epidemiological picture in Latin America; 4) NCL-like pathology studies in progress. The Translational Research Program was highly efficient in addressing the misdiagnosis/ underdiagnosis in the NCL disorders. The study of "orphan diseases" in a public administrated hospital should be adopted by the health systems, as it positively impacts upon the family's quality of life, the collection of epidemiological data, and triggers research advances. This article is part of a Special Issue entitled: "Current Research on the Neuronal Ceroid Lipofuscinoses (Batten Disease).
Copyright © 2015. Published by Elsevier B.V.
Available from: Stephan Storch
- "The disease-associated c.103 C > T (p. Arg35X) mutation causes a truncation of CLN7 after the first 34 amino acids with deletion of all 12 transmembrane domains presumably resulting in a non-functional protein  . The clinical manifestation of patients carrying this mutation is indistinguishable from patients with the p.T294K and p.P412L mutations, strongly suggesting that these mutations also lead to a complete loss of CLN7 function. "
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ABSTRACT: CLN7 is a polytopic lysosomal membrane glycoprotein of unknown function and is deficient in variant late infantile neuronal ceroid lipofuscinosis. Here we show that full-length CLN7 is proteolytically cleaved twice, once proximal to the used N-glycosylation sites in lumenal loop L9 and once distal to these sites. Cleavage occurs by cysteine proteases in acidic compartments and disruption of lysosomal targeting of CLN7 results in inhibition of proteolytic cleavage. The apparent molecular masses of the CLN7 fragments suggest that both cleavage sites are located within lumenal loop L9. The known disease-causing mutations, p.T294K and p.P412L, localized in lumenal loops L7 and L9, respectively, did not interfere with correct lysosomal targeting of CLN7 but enhanced its proteolytic cleavage in lysosomes. Incubation of cells with selective cysteine protease inhibitors and expression of CLN7 in gene-targeted mouse embryonic fibroblasts revealed that cathepsin L is required for one of the two proteolytic cleavage events. Our findings suggest that CLN7 is inactivated by proteolytic cleavage and that enhanced CLN7 proteolysis caused by missense mutations in selected luminal loops is associated with disease.
Available from: Bruno Bembi
- "The missense mutation c.881C>A (p.T294K) was found in most patients of Romany origin previously studied by Elleder et al. (Elleder et al., 1997). Haplotype analysis of these patients was consistent with the existence of a common founder effect (Kousi et al., 2009). The human CLN8 gene has been located to chromosome 8p23 (Ranta et al., 1999). "
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