Variant Late-infantile Neuronal Ceroid Lipofuscinosis Research Articles

CLN6 deficiency causes selective changes in the lysosomal protein composition.

Neuronal ceroid lipofuscinoses (NCLs) collectively account for the highest prevalence of inherited neurodegenerative diseases in childhood. This disease group is classified by the deposition of similar autofluorescence storage material in lysosomes that is accompanied by seizures, blindness and premature mortality in later disease stages. Defects in several genes affecting various proteins lead to NCL, one of them being CLN6, a transmembrane protein resident in the endoplasmic reticulum. Dysfunctionality of CLN6 causes variant late infantile NCL (vLINCL). The function of CLN6 and how its deficiency affects lysosomal integrity remains unknown. In this work, we performed a comparative proteomic analysis of isolated lysosomal fractions from liver tissue of nclf mice, a natural mouse model displaying a similar disease course than its human counterpart. We could identify a drastic reduction in the protein amounts of selected lysosomal proteins, amongst them several members of the NCL protein family. Most of these proteins were N-glycosylated, soluble hydrolases and their reduction in protein levels was verified by western blotting and enzymatic assays. Hereby we could directly link Cln6 dysfunction to changes in the lysosomal compartment and to other NCL forms.

MFSD8 Mutation Causing Neuronal Ceroid Lipofuscinosis Type 7 in a Bangladeshi Patient: A Rare Case Report and Review of Literature

The neuronal ceroid lipofuscinoses (NCLs) are a heterogeneous group of inherited neurodegenerative disorders. Their unifying clinical hallmarks are seizures, visual loss, myoclonus, ataxia, cognitive and motor regression which lead to early death. Based on the clinical onset of symptoms NCL-affected individuals have been classified into six categories. Fourteen genetic forms of NCL (CLN1 to CLN14) have been identified so far. The variant late-infantile form of the disease has been linked to CLN5, CLN6, CLN7 (MFSD8) and CLN8 mutations.We report a patient of 9 years from a consanguineous family who presented with progressive visual loss and seizures. Clinical Exome sequencing reveals a homozygous missense mutation in exon 11 of the MFSD8 gene (c.1235C>T, p.Pro412Leu). To our knowledge, this is the first report of MFSD8 gene mutation in a Bangladeshi patient with variant late-infantile NCL. This study also provides information regarding the phenotypic and molecular spectrum of CLN7 disease.

A novel pathogenic frameshift variant unmasked by a large de novo deletion at 13q21.33-q31.1 in a Chinese patient with neuronal ceroid lipofuscinosis type 5

BackgroundNeuronal ceroid lipofuscinosis type 5 (CLN5) is a rare form of neuronal ceroid lipofuscinoses (NCLs) which are a group of inherited neurodegenerative diseases characterized by progressive intellectual and motor deterioration, visual failure, seizures, behavioral changes and premature death. CLN5 was initially named Finnish variant late infantile NCL, it is now known to be present in other ethnic populations and with variable age of onset. Few CLN5 patients had been reported in Chinese population.Case presentationIn this paper, we report the symptoms of a Chinese patient who suffer from developmental regression and grand mal epilepsy for several years. The DNA was extracted from peripheral blood of proband and both parents, and then whole exome sequencing was performed using genomic DNA. Both sequence variants and copy number variants (CNVs) were analyzed and classified according to guidelines. As the result, a novel frameshift mutation c.718_719delAT/p.Met240fs in CLN5 and a de novo large deletion at 13q21.33-q31.1 which unmasked the frameshift mutation were identified in the proband. Despite the large de novo deletion, which can be classified as a pathogenic copy number variant (CNV), the patient’s clinical presentation is mostly consistent with that of CLN5, except for early developmental delay which is believed due to the large deletion. Both variants were detected simultaneously by exome sequencing.ConclusionsThis is the first report of whole gene deletion in combination with a novel pathogenic sequence variant in a CLN5 patient. The two mutations detected with whole exome sequencing simultaneously proved the advantage of the sequencing technology for genetic diagnostics.

An EEG Investigation of Sleep Homeostasis in Healthy and CLN5 Batten Disease Affected Sheep

Sheep have large brains with human-like anatomy, making them a useful species for studying brain function. Sleep homeostasis has not been studied in sheep. Here, we establish correlates of sleep homeostasis in sheep through a sleep deprivation experiment. We then use these correlates to elucidate the nature of sleep deficits in a naturally occurring ovine model of neuronal ceroid lipofuscinosis (NCL, Batten disease) caused by a mutation in CLN5 In humans, mutations in this gene lead to cortical atrophy and blindness, as well as sleep abnormalities. We recorded electroencephalograms (EEGs) from unaffected and early stage CLN5(-/-) (homozygous, affected) sheep over 3 consecutive days, the second day being the sleep deprivation day. In unaffected sheep, sleep deprivation led to increased EEG delta (0.5-4 Hz) power during non-rapid eye movement (NREM) sleep, increased time spent in the NREM sleep state, and increased NREM sleep bout length. CLN5(-/-) sheep showed comparable increases in time spent in NREM sleep and NREM sleep bout duration, verifying the presence of increased sleep pressure in both groups. Importantly, CLN5(-/-) sheep did not show the increase in NREM sleep delta power seen in unaffected sheep. This divergent delta power response is consistent with the known cortical degeneration in CLN5(-/-) sheep. We conclude that, whereas sleep homeostasis is present in CLN5(-/-) sheep, underlying CLN5(-/-) disease processes prevent its full expression, even at early stages. Such deficits may contribute to early abnormalities seen in sheep and patients and warrant further study. Sleep abnormalities pervade most neurological diseases, including the neuronal ceroid lipofuscinoses (NCLs). Here, we show that, in an ovine model of a variant late-infantile NCL, there is abnormal expression of sleep homeostasis. Whereas some sleep pressure correlates respond to sleep deprivation, the strongest electroencephalogram (EEG) correlate of sleep pressure, non-REM delta power, failed to increase. This highlights the relevance of sleep deficits in this disease, in which the drive for sleep exists but the underlying disease prevents its full expression. Sleep abnormalities could contribute to early disease symptoms such as behavioral disorder and cognitive decline. Our study also shows sleep homeostatic EEG correlates in sheep, opening up new opportunities for studying sleep in a large social mammal with complex human-like brain neuroanatomy.

Mutations in MFSD8, Encoding a Lysosomal Membrane Protein, Are Associated with Nonsyndromic Autosomal Recessive Macular Dystrophy

This study aimed to identify the genetic defects in 2 families with autosomal recessive macular dystrophy with central cone involvement. Case series. Two families and a cohort of 244 individuals with various inherited maculopathies and cone disorders. Genome-wide linkage analysis and exome sequencing were performed in 1 large family with 5 affected individuals. In addition, exome sequencing was performed in the proband of a second family. Subsequent analysis of the identified mutations in 244 patients was performed by Sanger sequencing or restriction enzyme digestion. The medical history of individuals carrying the MFSD8 variants was reviewed and additional ophthalmic examinations were performed, including electroretinography (ERG), multifocal ERG (mfERG), perimetry, optical coherence tomography (OCT), fundus autofluorescence, and fundus photography. MFSD8 variants, age at diagnosis, visual acuity, fundus appearance, color vision defects, visual field, ERG, mfERG, fundus autofluorescence, and OCT findings. Compound heterozygous variants in MFSD8, a gene encoding a lysosomal transmembrane protein, were identified in 2 families with macular dystrophy with a normal or subnormal ERG, but reduced mfERG. In both families, a heterozygous missense variant p.Glu336Gln was identified, which was predicted to have a mild effect on the protein. In the first family, a protein-truncating variant (p.Glu381*) was identified on the other allele, and in the second family, a variant (c.1102G>C) was identified that results in a splicing defect leading to skipping of exon 11 (p.Lys333Lysfs*3). The p.Glu336Gln allele was found to be significantly enriched in patients with maculopathies and cone disorders (6/488) compared with ethnically matched controls (35/18 682; P < 0.0001), suggesting that it may act as a genetic modifier. In this study, we identified variants in MFSD8 as a novel cause of nonsyndromic autosomal recessive macular dystrophy with central cone involvement. Affected individuals showed no neurologic features typical for variant late-infantile neuronal ceroid lipofuscinosis (vLINCL), a severe and devastating multisystem lysosomal storage disease previously associated with mutations in MFSD8. We propose a genotype-phenotype model in which a combination of a severe and a mild variant cause nonsyndromic macular dystrophy with central cone involvement, and 2 severe mutations cause vLINCL.

Apoptotic Photoreceptor Loss and Altered Expression of Lysosomal Proteins in thenclfMouse Model of Neuronal Ceroid Lipofuscinosis

Mutations in the CLN6 gene cause variant late-infantile neuronal ceroid lipofuscinosis, a lysosomal storage disorder clinically characterized by progressive loss of vision, dementia, seizures, and early death. Here, we analyzed the time course of photoreceptor loss and the role of lysosomes in nclf mice, an animal model of the human CLN6 disease. Labeling of apoptotic cells, activated astrocytes, and Müller cells, and expression analyses of glial fibrillary acidic protein, rhodopsin, and lysosomal proteins were performed on nclf mice during the course of retinal degeneration. In addition, the distribution and variability of storage material was examined at the ultrastructural level. Progressive apoptotic loss of photoreceptor cells was observed in nclf mice, resulting in reduction of the outer nuclear layer to approximately 3 rows of photoreceptor cells at 9 months of age. Onset of reactive gliosis was observed in 1-month-old nclf mice. Ultrastructural analysis revealed lysosomal storage material containing curvilinear and fingerprint-like inclusions in various retinal cell types. Expression levels of soluble mannose 6-phosphate-containing lysosomal enzymes, such as cathepsin D and the lysosomal membrane protein Lamp1, were increased in retinal cells of nclf mice. Accumulation of heterogeneous nondegraded macromolecules in dysfunctional lysosomes and autolysosomes impairs photoreceptor cells, ultimately leading to early-onset apoptotic death with subsequent activation of astrocytes and Müller cells in the retina of nclf mice. The defined steps of photoreceptor degeneration suggest that nclf mice might serve as an ideal animal model for experimental therapeutic approaches aimed at attenuating vision loss in neuronal ceroid lipofuscinosis.

CLN6 disease caused by the same mutation originating in Pakistan has varying pathology

The neuronal ceroid lipofuscinoses (NCLs), the most common neurodegenerative diseases in children, are characterised by storage of autofluorescent material that has a characteristic ultrastructure. We report two families with variant late infantile NCL, both originating from Pakistan. Probands from both families were homozygous for the same mutation (c.316dupC) but had variable pathology to that currently thought to be typical for CLN6 disease, late infantile variant. The observed pathology of one proband resembled condensed fingerprints, previously described in late infantile CLN7 and CLN8 diseases, and pathology from the second proband was thought to be absent even after repeated skin biopsy, but observed after review. This mutation is the most common NCL mutation in families originating from Pakistan and could be prioritised for testing. Finally, this report contains the first prenatal diagnosis for late infantile CLN6 disease, initially made on the basis of EM and now confirmed by mutation analysis.

Atypical juvenile neuronal ceroid lipofuscinosis: A report of three cases

The diagnosis of juvenile neuronal ceroid lipofuscinosis (JNCL) is usually based on age of onset, initial clinical symptoms, clinical progression, and pathologic findings. Our cases manifested atypical clinical symptomatology and/or pathologic findings and therefore, represent variant forms of JNCL. Case 1 and 2 presented with slow developmental regression from the age of 4 years and became blind and wheelchair bound at around 8 years. Pathologic finding of lymphocytes showed fingerprint inclusion which was consistent with JNCL. Mutational analysis was positive for CLN5 which usually presents as variant late infantile NCL (LINCL) and more common in Finnish population. Case 3 presented with progressive visual loss from the age of 8 years. Clinical symptomatology and age of onset were similar to that of JNCL but was found to have low palmitoyl protein thioesterase, granular inclusion body, and CLN1 mutation, thus representing milder form of INCL. These three cases demonstrated phenotypic-genotypic variations. Pertinent issues relating diagnostic difficulties, ophthalmologic, neuroradiological, and laboratory aspects are discussed.

Disruption of the Autophagy-Lysosome Pathway Is Involved in Neuropathology of the nclf Mouse Model of Neuronal Ceroid Lipofuscinosis

Variant late-infantile neuronal ceroid lipofuscinosis, a fatal lysosomal storage disorder accompanied by regional atrophy and pronounced neuron loss in the brain, is caused by mutations in the CLN6 gene. CLN6 is a non-glycosylated endoplasmic reticulum (ER)-resident membrane protein of unknown function. To investigate mechanisms contributing to neurodegeneration in CLN6 disease we examined the nclf mouse, a naturally occurring model of the human CLN6 disease. Prominent autofluorescent and electron-dense lysosomal storage material was found in cerebellar Purkinje cells, thalamus, hippocampus, olfactory bulb and in cortical layer II to V. Another prominent early feature of nclf pathogenesis was the localized astrocytosis that was evident in many brain regions and the more widespread microgliosis. Expression analysis of mutant Cln6 found in nclf mice demonstrated synthesis of a truncated protein with a reduced half-life. Whereas the rapid degradation of the mutant Cln6 protein can be inhibited by proteasomal inhibitors, there was no evidence for ER stress or activation of the unfolded protein response in various brain areas during postnatal development. Age-dependent increases in LC3-II, ubiquitinated proteins, and neuronal p62-positive aggregates were observed, indicating a disruption of the autophagy-lysosome degradation pathway of proteins in brains of nclf mice, most likely due to defective fusion between autophagosomes and lysosomes. These data suggest that proteasomal degradation of mutant Cln6 is sufficient to prevent the accumulation of misfolded Cln6 protein, whereas lysosomal dysfunction impairs constitutive autophagy promoting neurodegeneration.

Variant late-infantile neuronal ceroid lipofuscinosis due to a novel heterozygous CLN8 mutation and de novo 8p23.3 deletion

Variant late-infantile neuronal ceroid lipofuscinosis due to a novel heterozygous CLN8 mutation and de novo 8p23.3 deletion

Kufs Disease, the Major Adult Form of Neuronal Ceroid Lipofuscinosis, Caused by Mutations in CLN6

The molecular basis of Kufs disease is unknown, whereas a series of genes accounting for most of the childhood-onset forms of neuronal ceroid lipofuscinosis (NCL) have been identified. Diagnosis of Kufs disease is difficult because the characteristic lipopigment is largely confined to neurons and can require a brain biopsy or autopsy for final diagnosis. We mapped four families with Kufs disease for whom there was good evidence of autosomal-recessive inheritance and found two peaks on chromosome 15. Three of the families were affected by Kufs type A disease and presented with progressive myoclonus epilepsy, and one was affected by type B (presenting with dementia and motor system dysfunction). Sequencing of a candidate gene in one peak shared by all four families identified no mutations, but sequencing of CLN6, found in the second peak and shared by only the three families affected by Kufs type A disease, revealed pathogenic mutations in all three families. We subsequently sequenced CLN6 in eight other families, three of which were affected by recessive Kufs type A disease. Mutations in both CLN6 alleles were found in the three type A cases and in one family affected by unclassified Kufs disease. Mutations in CLN6 are the major cause of recessive Kufs type A disease. The phenotypic differences between variant late-infantile NCL, previously found to be caused by CLN6, and Kufs type A disease are striking; there is a much later age at onset and lack of visual involvement in the latter. Sequencing of CLN6 will provide a simple diagnostic strategy in this disorder, in which definitive identification usually requires invasive biopsy.

P05.12 The first case of genetically proven variant late-infantile neuronal ceroid lipofuscinosis in Bulgaria harbors the founder CLN7/MFSD8 mutation in Roma

P05.12 The first case of genetically proven variant late-infantile neuronal ceroid lipofuscinosis in Bulgaria harbors the founder CLN7/MFSD8 mutation in Roma

Neuronal Ceroid Lipofuscinosis in Qatar: Report of a Novel Mutation in Ceroid-Lipofuscinosis, Neuronal 5 in the Arab Population

This study sought to genetically define the first family diagnosed with neuronal ceroid lipofuscinosis from Qatar. Onset was in late infancy (3 years), and sequencing in the affected children revealed a novel homozygous c.613C>T change in exon 3 of ceroid-lipofuscinosis, neuronal 5, corresponding to a missense mutation of a conserved amino acid, p.Pro205Ser. The clinical manifestations of the disease in this family largely resemble those of ceroid-lipofuscinosis, neuronal 5 disease, variant late infantile that was first described in Finland and include mental decline, visual deterioration, ataxia, and epileptic seizures. This description of ceroid-lipofuscinosis, neuronal 5 disease in an Arab family adds to the clinical and molecular diversity of the variant late-infantile neuronal ceroid lipofuscinoses, which were originally reported in Europe and are increasingly recognized in other populations.

Distinct early molecular responses to mutations causing vLINCL and JNCL presage ATP synthase subunit C accumulation in cerebellar cells.

Variant late-infantile neuronal ceroid lipofuscinosis (vLINCL), caused by CLN6 mutation, and juvenile neuronal ceroid lipofuscinosis (JNCL), caused by CLN3 mutation, share clinical and pathological features, including lysosomal accumulation of mitochondrial ATP synthase subunit c, but the unrelated CLN6 and CLN3 genes may initiate disease via similar or distinct cellular processes. To gain insight into the NCL pathways, we established murine wild-type and CbCln6 nclf/nclf cerebellar cells and compared them to wild-type and CbCln3 Δex7/8/Δex7/8 cerebellar cells. CbCln6 nclf/nclf cells and CbCln3 Δex7/8/Δex7/8 cells both displayed abnormally elongated mitochondria and reduced cellular ATP levels and, as cells aged to confluence, exhibited accumulation of subunit c protein in Lamp 1-positive organelles. However, at sub-confluence, endoplasmic reticulum PDI immunostain was decreased only in CbCln6 nclf/nclf cells, while fluid-phase endocytosis and LysoTracker® labeled vesicles were decreased in both CbCln6 nclf/nclf and CbCln3 Δex7/8/Δex7/8 cells, though only the latter cells exhibited abnormal vesicle subcellular distribution. Furthermore, unbiased gene expression analyses revealed only partial overlap in the cerebellar cell genes and pathways that were altered by the Cln3 Δex7/8 and Cln6 nclf mutations. Thus, these data support the hypothesis that CLN6 and CLN3 mutations trigger distinct processes that converge on a shared pathway, which is responsible for proper subunit c protein turnover and neuronal cell survival.

Expression and lysosomal targeting of CLN7, a major facilitator superfamily transporter associated with variant late-infantile neuronal ceroid lipofuscinosis

Neuronal ceroid lipofuscinoses (NCLs) constitute a group of progressive neurodegenerative disorders resulting from mutations in at least eight different genes. Mutations in the most recently identified NCL gene, MFSD8/CLN7, underlie a variant of late-infantile NCL (vLINCL). The MFSD8/CLN7 gene encodes a polytopic protein with unknown function, which shares homology with ion-coupled membrane transporters. In this study, we confirmed the lysosomal localization of the native CLN7 protein. This localization of CLN7 is not impaired by the presence of pathogenic missense mutations or after genetic ablation of the N-glycans. Expression of chimeric and full-length constructs showed that lysosomal targeting of CLN7 is mainly determined by an N-terminal dileucine motif, which specifically binds to the heterotetrameric adaptor AP-1 in vitro. We also show that CLN7 mRNA is more abundant in neurons than astrocytes and microglia, and that it is expressed throughout rat brain, with increased levels in the granular layer of cerebellum and hippocampal pyramidal cells. Interestingly, this cellular and regional distribution is in good agreement with the autofluorescent lysosomal storage and cell loss patterns found in brains from CLN7-defective patients. Overall, these data highlight lysosomes as the primary site of action for CLN7, and suggest that the pathophysiology underpinning CLN7-associated vLINCL is a cell-autonomous process.

CLN5 mutations are frequent in juvenile and late-onset non-Finnish patients with NCL

To explore a potential expansion of the phenotypic and genotypic characteristics of Finnish variant late-infantile neuronal ceroid lipofuscinosis (NCL), we screened a collection of 47 patients with clinically diagnosed NCL in whom no molecular diagnosis had been made. We used PCR amplification of genomic DNA, followed by fluorescent-labeled dideoxy-nucleotide chain termination sequencing and multiplex ligation-dependent probe amplification, to screen our cohort of patients for mutations in CLN5. We collected ethnic background, clinical, and pathologic information, as available, to clarify the breadth of CLN5 disease expression and to explore possible genotype-phenotype correlations. We identified 10 patients with pathogenic CLN5 mutations, including 11 mutations not previously described: 4 missense, 5 out-of-frame insertion/deletion mutations, and 2 large intragenic deletions. We also documented 3 previously reported CLN5 mutations. The age at disease onset in this cohort is predominantly juvenile rather than late infantile. Importantly, we have identified 2 adult-onset patients who share a common pathogenic allele. The majority of patients presented with motor and visual impairments and not seizures. In those patients with available longitudinal data, most had progressed to global neurodevelopmental and visual failure with seizures within 1 to 4 years. Our study suggests that CLN5 mutations 1) are more common in patients with neuronal ceroid lipofuscinosis (NCL) than previously reported, 2) are found in non-Finnish NCL patients of broad ethnic diversity, and 3) can be identified in NCL patients with disease onset in adult and juvenile epochs. CLN5 genetic testing is warranted in a wider population with clinical and pathologic features suggestive of an NCL disorder.

The neuronal ceroid lipofuscinosis protein CLN5: new insights into cellular maturation, transport, and consequences of mutations

Neuronal ceroid lipofuscinoses (NCLs) represent a group of children's inherited neurodegenerative disorders caused by mutations in at least eight different genes. Mutations in the CLN5 gene result in the Finnish variant late infantile NCL characterized by gradual loss of vision, epileptic seizures, and mental deterioration. The CLN5 gene encodes a lysosomal glycoprotein of unidentified function. In this study, we have used both transient and stable expression systems for the characterization of CLN5, focusing on the localization, processing, and intracellular trafficking. We show that CLN5 is proteolytically cleaved, and that the mature polypeptide is transported to the lysosomes. Our data provide the first evidence that soluble CLN5 protein can also undergo mannose-6-phosphate receptor-independent trafficking to the lysosomes. We studied the localization and maturation of the CLN5 carrying the previously uncharacterized vLINCL disease causing mutations in HeLa cells. All analyzed disease mutations disturb the lysosomal trafficking of the mutated CLN5 proteins. The level of lysosomal targeting does not correlate, however, to disease onset, indicating that CLN5 may also function outside lysosomes. This study furthers our understanding of the basic properties of the CLN5 protein, necessary for the characterization of the consequences of disease mutations and for the planning of future therapies for vLINCL.

Molecular correlates of axonal and synaptic pathology in mouse models of Batten disease

Neuronal ceroid lipofuscinoses (NCLs; Batten disease) are collectively the most frequent autosomal-recessive neurodegenerative disease of childhood, but the underlying cellular and molecular mechanisms remain unclear. Several lines of evidence have highlighted the important role that non-somatic compartments of neurons (axons and synapses) play in the instigation and progression of NCL pathogenesis. Here, we report a progressive breakdown of axons and synapses in the brains of two different mouse models of NCL: Ppt1−/− model of infantile NCL and Cln6nclf model of variant late-infantile NCL. Synaptic pathology was evident in the thalamus and cortex of these mice, but occurred much earlier within the thalamus. Quantitative comparisons of expression levels for a subset of proteins previously implicated in regulation of axonal and synaptic vulnerability revealed changes in proteins involved with synaptic function/stability and cell-cycle regulation in both strains of NCL mice. Protein expression changes were present at pre/early-symptomatic stages, occurring in advance of morphologically detectable synaptic or axonal pathology and again displayed regional selectivity, occurring first within the thalamus and only later in the cortex. Although significant differences in individual protein expression profiles existed between the two NCL models studied, 2 of the 15 proteins examined (VDAC1 and Pttg1) displayed robust and significant changes at pre/early-symptomatic time-points in both models. Our study demonstrates that synapses and axons are important early pathological targets in the NCLs and has identified two proteins, VDAC1 and Pttg1, with the potential for use as in vivo biomarkers of pre/early-symptomatic axonal and synaptic vulnerability in the NCLs.

Progressive thalamocortical neuron loss in Cln5 deficient mice: Distinct effects in Finnish variant late infantile NCL

Finnish variant LINCL (vLINCL Fin) is the result of mutations in the CLN5 gene. To gain insights into the pathological staging of this fatal pediatric disorder, we have undertaken a stereological analysis of the CNS of Cln5 deficient mice ( Cln5 −/− ) at different stages of disease progression. Consistent with human vLINCL Fin, these Cln5 −/− mice displayed a relatively late onset regional atrophy and generalized cortical thinning and synaptic pathology, preceded by early and localized glial responses within the thalamocortical system. However, in marked contrast to other forms of NCL, neuron loss in Cln5 −/− mice began in the cortex and only subsequently occurred within thalamic relay nuclei. Nevertheless, as in other NCL mouse models, this progressive thalamocortical neuron loss was still most pronounced within the visual system. These data provide unexpected evidence for a distinctive sequence of neuron loss in the thalamocortical system of Cln5 −/− mice, diametrically opposed to that seen in other forms of NCL.

Mutations in CLN7/MFSD8 are a common cause of variant late-infantile neuronal ceroid lipofuscinosis

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.