Adult-onset autosomal recessive ataxia associated with neuronal ceroid lipofuscinosis type 5 gene (CLN5) mutations

The conserved cellular roles of CLN proteins: Novel insights from Dictyostelium discoideum

The neuronal ceroid lipofuscinoses (NCLs), collectively referred to as Batten disease, are a group of fatal neurodegenerative disorders that primarily affect children. The etiology of Batten disease is linked to mutations in 13 genes that encode distinct CLN proteins, whose functions have yet to be fully elucidated. The social amoeba Dictyostelium discoideum has been adopted as an efficient and powerful model system for studying the diverse cellular roles of CLN proteins. The genome of D. discoideum encodes several homologs of human CLN proteins, and a growing body of literature supports the conserved roles and networking of CLN proteins in D. discoideum and humans. In humans, CLN proteins have diverse cellular roles related to autophagy, signal transduction, lipid homeostasis, lysosomal ion homeostasis, and intracellular trafficking. Recent work also indicates that CLN proteins play an important role in protein secretion. Remarkably, many of these findings have found parallels in studies with D. discoideum. Accordingly, this review will highlight the translatable value of novel work with D. discoideum in the field of NCL research and propose further avenues of research using this biomedical model organism for studying the NCLs.

A novel CLN5 mutation in Turkish patient with variant late-onset neuronal ceroid lipofuscinosis and recurrent fractures that causes severe morbidity

Neuronal ceroid lipofuscinosis (NCL) is characterized by ataxia, epilepsy, mental and motor deterioration, and visual loss. The phenotype of patients is highly heterogeneous. We report a patient with late-infantile-onset psychomotor retardation, visual loss, seizure, movement disorder, and recurrent bone fractures. Clinical exome sequencing revealed a novel homozygous c.1113_1116del, p.Y371fs mutation in CLN5. No variant was detected associated with simple bone cyst. While NCL disease is difficult disease in itself, recurrent fractures significantly increased morbidity. This case report contributes to genotypic spectrum of CLN5 and emphasizes clinical importance of Turkish patients with CLN5 mutations, and non-NCL factors/diseases can adversely affect morbidity.

Dictyostelium discoideum as a Model for Investigating Neurodegenerative Diseases

The social amoeba Dictyostelium discoideum is a model organism that is used to investigate many cellular processes including chemotaxis, cell motility, cell differentiation, and human disease pathogenesis. While many single-cellular model systems lack homologs of human disease genes, Dictyostelium's genome encodes for many genes that are implicated in human diseases including neurodegenerative diseases. Due to its short doubling time along with the powerful genetic tools that enable rapid genetic screening, and the ease of creating knockout cell lines, Dictyostelium is an attractive model organism for both interrogating the normal function of genes implicated in neurodegeneration and for determining pathogenic mechanisms that cause disease. Here we review the literature involving the use of Dictyostelium to interrogate genes implicated in neurodegeneration and highlight key questions that can be addressed using Dictyostelium as a model organism.

Autosomal recessive adult onset ataxia

Autosomal recessive ataxias (ARCA) represent a complex group of diseases ranging from primary ataxias to rare and complex metabolic disorders in which ataxia is a part of the clinical picture. Small number of ARCA manifest exclusively in adulthood, while majority of typical childhood onset ARCA may also start later with atypical clinical presentation. We have systematically searched the literature for ARCA with adult onset, both in the group of primary ataxias including those that are less frequently described in isolated or in a small number of families, and also in the group of complex and metabolic diseases in which ataxia is only part of the clinical picture. We propose an algorithm that could be used when encountering a patient with adult onset sporadic or recessive ataxia in whom the acquired causes are excluded. ARCA are frequently neglected in the differential diagnosis of adult-onset ataxias. Rising awareness of their clinical significance is important, not only because some of these disorders may be potentially treatable, but also for prognostic implications and inclusion of patients to future clinical trials with disease modifying agents.

Ocular Manifestations of Neuronal Ceroid Lipofuscinoses

Neuronal ceroid lipofuscinoses (NCLs) are a group of rare neurodegenerative storage disorders associated with devastating visual prognosis, with an incidence of 1/1,000,000 in the United States and comparatively higher incidence in European countries. The pathophysiological mechanisms causing NCLs occur due to enzymatic or transmembrane defects in various sub-cellular organelles including lysosomes, endoplasmic reticulum, and cytoplasmic vesicles. NCLs are categorized into different types depending upon the underlying cause i.e., soluble lysosomal enzyme deficiencies or non-enzymatic deficiencies (functions of identified proteins), which are sub-divided based on an axial classification system. In this review, we have evaluated the current evidence in the literature and reported the incidence rates, underlying mechanisms and currently available management protocols for these rare set of neuroophthalmological disorders. Additionally, we also highlighted the potential therapies under development that can expand the treatment of these rare disorders beyond symptomatic relief.

A lysosomal enigma CLN5 and its significance in understanding neuronal ceroid lipofuscinosis

Neuronal Ceroid Lipofuscinosis (NCL), also known as Batten disease, is an incurable childhood brain disease. The thirteen forms of NCL are caused by mutations in thirteen CLN genes. Mutations in one CLN gene, CLN5, cause variant late-infantile NCL, with an age of onset between 4 and 7 years. The CLN5 protein is ubiquitously expressed in the majority of tissues studied and in the brain, CLN5 shows both neuronal and glial cell expression. Mutations in CLN5 are associated with the accumulation of autofluorescent storage material in lysosomes, the recycling units of the cell, in the brain and peripheral tissues. CLN5 resides in the lysosome and its function is still elusive. Initial studies suggested CLN5 was a transmembrane protein, which was later revealed to be processed into a soluble form. Multiple glycosylation sites have been reported, which may dictate its localisation and function. CLN5 interacts with several CLN proteins, and other lysosomal proteins, making it an important candidate to understand lysosomal biology. The existing knowledge on CLN5 biology stems from studies using several model organisms, including mice, sheep, cattle, dogs, social amoeba and cell cultures. Each model organism has its advantages and limitations, making it crucial to adopt a combinatorial approach, using both human cells and model organisms, to understand CLN5 pathologies and design drug therapies. In this comprehensive review, we have summarised and critiqued existing literature on CLN5 and have discussed the missing pieces of the puzzle that need to be addressed to develop an efficient therapy for CLN5 Batten disease.

Association of the Recurrent Rare Variant c.415T>C p.Phe139Leu in CLN5 With a Recessively Inherited Macular Dystrophy

Importance

Homozygous variants in the neuronal ceroid lipofuscinosis type 5 (CLN5) gene are associated with neuronal ceroid lipofuscinosis, a progressive neurologic disorder that leads to ataxia, seizures, and early death. The association between a homozygous variant in this gene and a macular dystrophy is described here.

Objective

To describe an autosomal recessive macular dystrophy associated with a recurrent variant in CLN5.

Design, Setting, and Participants

This cohort study took place at a national referral center and had a follow-up duration ranging between 1 and 5 years. All patients who were identified to carry a specific homozygous missense variant in CLN5, among more than 2000 patients who were diagnosed with or suspected to have retinal dystrophies, who did not carry this variant, were included. Data were collected between June 2014 and September 2020.

Exposures

All patients who were sampled for DNA analysis due to molecularly unconfirmed retinal dystrophy and who were subsequently identified to carry the homozygous missense variant c.415T>C (p.Phe139Leu) in CLN5 were included, while patients who did not carry the variant were excluded.

Main Outcomes and Measures

Retinal phenotype associated with this specific homozygous missense variant in CLN5.

Results

Seven affected patients (mean [SD] age, 43 [18] years; age range, 33-52 years; 5 male) carried the homozygous missense in CLN5. All patients were diagnosed as having a macular dystrophy. Four patients had mild electroretinographic alterations. All patients had hypoautofluorescent maculas with retinal thinning (central subfield thickness, 80 µm). Visual acuity ranged between 2/200 and 20/100. Neurologic symptoms were mild (dizziness) in 5 patients and absent in 2 patients. Neuroimaging demonstrated cerebellar atrophy and white matter lesions, respectively, in 2 patients.

Conclusions and Relevance

These results suggest that CLN5, similar to CLN7, may be associated with isolated macular dystrophy as well as neuronal ceroid lipofuscinosis. The variant c.415T>C p.Phe139Leu does not seem to be associated with any prominent neurologic disease at least until the fourth to sixth decades of life. These findings may imply a specific role of CLN5 in macular neurons. Additional study is suggested, such as molecular screening for this variant in cohorts of patients with undiagnosed macular dystrophies and biological studies of its molecular effects.

Functional Analysis of a Novel CLN5 Mutation Identified in a Patient With Neuronal Ceroid Lipofuscinosis

Neuronal ceroid lipofuscinoses (NCLs) are a group of autosomal recessive inherited neurodegenerative disorders mainly affecting children, and at least 13 causative genes (CLN1 to CLN8 and CLN10 to CLN14) have been identified. Here, we reported a novel homozygous missense mutation (c.434G > C, p.Arg145Pro) identified in CLN5 gene via whole exome sequencing in a 5-year-old girl. The patient first presented paroxysmal epilepsy associated with vomiting, followed by progressive regression in walking, vision, intelligence and speaking. Combining the molecular and clinical analysis, the diagnosis of NCL could be made, although the missense mutation (c.434G > C, p.Arg145Pro) in CLN5 was evaluated to be a variant of uncertain significance according to American College of Medical Genetics and Genomics (ACMG) standard. We further performed expression and localization studies and our results provide evidence of impaired cellular trafficking of CLN5 to lysosome, indicating that this mutation might be deleterious to the function of CLN5 for its mislocalization. Our study demonstrated the efficacy of next generation sequencing in molecular diagnosis, and a deleterious effect of the variant discovered in our patient on CLN5, triggering the NCL 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

BACKGROUND

Neuronal 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 PRESENTATION

In 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.

CONCLUSIONS

This 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.

The Neuronal Ceroid Lipofuscinoses-Linked Loss of Function CLN5 and CLN8 Variants Disrupt Normal Lysosomal Function

Neuronal ceroid lipofuscinoses (NCLs) are a group of neurodegenerative disorders caused by mutations in fourteen distinct ceroid lipofuscinoses, neuronal (CLN) genes described with various severe symptoms such as seizures, visual failure, motor decline, and progressive cognitive deterioration. The current research represents novel CLN5 (c.741G > A) and CLN8 (c.565delT) mutations in two different Iranian families with late-infantile NCL (LINCL) and their relatives by using whole-exome sequencing (WES). The first family had a 10-year-old male with consanguineous parents and severe NCL symptoms, including motor clumsiness, telangiectasia, and cerebellar atrophy. The second family with a child who suffered from nystagmus rotation, motor difficulties, and seizure was a 5-year-old male with consanguineous parent. WES of probands 1 and 2 revealed homozygotic mutations in exon 4 of CLN5 (c.741G > A, p.W247X) and deletion in exon 3 (c.565delT, p.F189fs) of CLN8, respectively. Both patients' parents were heterozygous for these alterations. In concordance with previous studies, our results indicate that pathogenic mutations in CLN genes, especially CLN5 and 8, are a main cause of LINCL; these results also suggest that LINCL is not a regionally or nationally dependent disorder and can occur in any ethnic group despite the fact that some populations may be more at risk. Consequently, CLN gene screening for patients with typical signs of LINCL is recommended.

Therapeutic landscape for Batten disease: current treatments and future prospects

Batten disease (also known as neuronal ceroid lipofuscinoses) constitutes a family of devastating lysosomal storage disorders that collectively represent the most common inherited paediatric neurodegenerative disorders worldwide. Batten disease can result from mutations in 1 of 13 genes. These mutations lead to a group of diseases with loosely overlapping symptoms and pathology. Phenotypically, patients with Batten disease have visual impairment and blindness, cognitive and motor decline, seizures and premature death. Pathologically, Batten disease is characterized by lysosomal accumulation of autofluorescent storage material, glial reactivity and neuronal loss. Substantial progress has been made towards the development of effective therapies and treatments for the multiple forms of Batten disease. In 2017, cerliponase alfa (Brineura), a tripeptidyl peptidase enzyme replacement therapy, became the first globally approved treatment for CLN2 Batten disease. Here, we provide an overview of the promising therapeutic avenues for Batten disease, highlighting current FDA-approved clinical trials and prospective future treatments.

Recent Insights into NCL Protein Function Using the Model Organism Dictyostelium discoideum

The neuronal ceroid lipofuscinoses (NCLs) are a group of devastating neurological disorders that have a global distribution and affect people of all ages. Commonly known as Batten disease, this form of neurodegeneration is linked to mutations in 13 genetically distinct genes. The precise mechanisms underlying the disease are unknown, in large part due to our poor understanding of the functions of NCL proteins. The social amoeba Dictyostelium discoideum has proven to be an exceptional model organism for studying a wide range of neurological disorders, including the NCLs. The Dictyostelium genome contains homologs of 11 of the 13 NCL genes. Its life cycle, comprised of both single-cell and multicellular phases, provides an excellent system for studying the effects of NCL gene deficiency on conserved cellular and developmental processes. In this review, we highlight recent advances in NCL research using Dictyostelium as a biomedical model.

Novel Mutations in CLN5 of Chinese Patients With Neuronal Ceroid Lipofuscinosis

Neuronal ceroid lipofuscinosis is a hereditary disease, and ceroid-lipofuscinosis neuronal protein 5 (CLN5) has been proved to be associated with neuronal ceroid lipofuscinosis. Here we report 3 patients from 2 families diagnosed with CLN5 neuronal ceroid lipofuscinosis. Whole genome sequencing of DNAs from 3 patients and their families revealed 3 novel homozygous mutations, including 1 deletion CLN5.c718 719delAT and 2 missense mutations c.1082T>C and c.623G>A. We reviewed 278 papers about neuronal ceroid lipofuscinosis resulting from CLN5 mutations and compared Chinese cases with 27 European and American cases. The overall age of onset of European and American patients occur mainly at 3 to 6 years (66%, 18/27), 100% (27/27) of patients had psychomotor regression, 99% (26/27) patients presented vision decline, and 70% (19/27) of patients suffered seizures. In China, the age of onset in 3 patients was 5 years, but for 1 patient it was at 17 months. Four Chinese patients presented psychomotor deterioration and seizures; only 1 had visual problems.

Secretion and function of Cln5 during the early stages of Dictyostelium development

Mutations in CLN5 cause neuronal ceroid lipofuscinosis (NCL), a currently untreatable neurodegenerative disorder commonly known as Batten disease. Several genetic models have been generated to study the function of CLN5, but one limitation has been the lack of a homolog in lower eukaryotic model systems. Our previous work revealed a homolog of CLN5 in the social amoeba Dictyostelium discoideum. We used a Cln5-GFP fusion protein to show that the protein is secreted and functions as a glycoside hydrolase in Dictyostelium. Importantly, we also revealed this to be the molecular function of human CLN5. In this study, we generated an antibody against Cln5 to show that the endogenous protein is secreted during the early stages of Dictyostelium development. Like human CLN5, the Dictyostelium homolog is glycosylated and requires this post-translational modification for secretion. Cln5 secretion bypasses the Golgi complex, and instead, occurs via an unconventional pathway linked to autophagy. Interestingly, we observed co-localization of Cln5 and GFP-Cln3 as well as increased secretion of Cln5 and Cln5-GFP in cln3- cells. Loss of Cln5 causes defects in adhesion and chemotaxis, which intriguingly, has also been reported for Dictyostelium cells lacking Cln3. Finally, autofluorescence was detected in cln5- cells, which is consistent with observations in mammalian systems. Together, our data support a function for Cln5 during the early stages of multicellular development, provide further evidence for the molecular networking of NCL proteins, and provide insight into the mechanisms that may underlie CLN5 function in humans.

Cln5 is secreted and functions as a glycoside hydrolase in Dictyostelium

Ceroid lipofuscinosis neuronal 5 (CLN5) is a member of a family of proteins that are linked to neuronal ceroid lipofuscinosis (NCL). This devastating neurological disorder, known commonly as Batten disease, affects all ages and ethnicities and is currently incurable. The precise function of CLN5, like many of the NCL proteins, remains to be elucidated. In this study, we report the localization, molecular function, and interactome of Cln5, the CLN5 homolog in the social amoeba Dictyostelium discoideum. Residues that are glycosylated in human CLN5 are conserved in the Dictyostelium homolog as are residues that are mutated in patients with CLN5 disease. Dictyostelium Cln5 contains a putative signal peptide for secretion and we show that the protein is secreted during growth and starvation. We also reveal that both Dictyostelium Cln5 and human CLN5 are glycoside hydrolases, providing the first evidence in any system linking a molecular function to CLN5. Finally, immunoprecipitation coupled with mass spectrometry identified 61 proteins that interact with Cln5 in Dictyostelium. Of the 61 proteins, 67% localize to the extracellular space, 28% to intracellular vesicles, and 20% to lysosomes. A GO term enrichment analysis revealed that a majority of the interacting proteins are involved in metabolism, catabolism, proteolysis, and hydrolysis, and include other NCL-like proteins (e.g., Tpp1/Cln2, cathepsin D/Cln10, cathepsin F/Cln13) as well as proteins linked to Cln3 function in Dictyostelium (e.g., AprA, CfaD, CadA). In total, this work reveals a CLN5 homolog in Dictyostelium and further establishes this organism as a complementary model system for studying the functions of proteins linked to NCL in humans.

Loss of Cln5 causes altered neurogenesis in a mouse model of a childhood neurodegenerative disorder

Neural stem/progenitor cells (NPCs) generate new neurons in the brain throughout an individual's lifetime in an intricate process called neurogenesis. Neurogenic alterations are a common feature of several adult-onset neurodegenerative diseases. The neuronal ceroid lipofuscinoses (NCLs) are the most common group of inherited neurodegenerative diseases that mainly affect children. Pathological features of the NCLs include accumulation of lysosomal storage material, neuroinflammation and neuronal degeneration, yet the exact cause of this group of diseases remains poorly understood. The function of the CLN5 protein, causative of the CLN5 disease form of NCL, is unknown. In the present study, we sought to examine neurogenesis in the neurodegenerative disorder caused by loss of Cln5 Our findings demonstrate a newly identified crucial role for CLN5 in neurogenesis. We report for the first time that neurogenesis is increased in Cln5-deficient mice, which model the childhood neurodegenerative disorder caused by loss of Cln5 Our results demonstrate that, in Cln5 deficiency, proliferation of NPCs is increased, NPC migration is reduced and NPC differentiation towards the neuronal lineage is increased concomitantly with functional alterations in the NPCs. Moreover, the observed impairment in neurogenesis is correlated with increased expression of the pro-inflammatory cytokine IL-1β. A full understanding of the pathological mechanisms that lead to disease and the function of the NCL proteins are critical for designing effective therapeutic approaches for this devastating neurodegenerative disorder.

Phenotype and natural history of variant late infantile ceroid-lipofuscinosis 5

AIM

To characterize the phenotypic profile of a cohort of children affected with CLN5, a rare form of neuronal ceroid-lipofuscinosis (NCL), and to trace the features of the natural history of the disease.

METHOD

Records of 15 children (nine males, six females) were obtained from the data sets of the DEM-CHILD International NCL Registry. Disease progression was measured by rating six functional domains at different time points along the disease course. All patients underwent mutation analysis of the CLN5 gene and ultrastructural investigations of peripheral tissues. Expression of the gene product, pCLN5, was characterized in vitro in six patients.

RESULTS

Disease onset was at 2 to 7 years 6 months of age: impaired learning and cognition were the most common early symptoms. Seizures occurred relatively late (median age 8y) and were the presenting symptoms in two children. Nine mutations were detected in 30 alleles, including six mutations predicting a truncated protein. Mixed cytosomes were observed by electron microscopy. Differences of disease progression were observed in two groups of patients and could be related to their genetic profile.

INTERPRETATION

Clinical features in a multicentre cohort of patients with CLN5 confirm that cognitive difficulties are early clinical markers of this condition. Severe mutations were associated with a more rapid decline of neurological function.

Induced Pluripotent Stem Cells Derived from a CLN5 Patient Manifest Phenotypic Characteristics of Neuronal Ceroid Lipofuscinoses

Neuronal ceroid lipofuscinoses (NCLs) are autosomal recessive progressive encephalopathies caused by mutations in at least 14 different genes. Despite extensive studies performed in different NCL animal models, the molecular mechanisms underlying neurodegeneration in NCLs remain poorly understood. To model NCL in human cells, we generated induced pluripotent stem cells (iPSCs) by reprogramming skin fibroblasts from a patient with CLN5 (ceroid lipofuscinosis, neuronal, 5) disease, the late infantile variant form of NCL. These CLN5 patient-derived iPSCs (CLN5Y392X iPSCs) harbouring the most common CLN5 mutation, c.1175_1176delAT (p.Tyr392X), were further differentiated into neural lineage cells, the most affected cell type in NCLs. The CLN5Y392X iPSC-derived neural lineage cells showed accumulation of autofluorescent storage material and subunit C of the mitochondrial ATP synthase, both representing the hallmarks of many forms of NCLs, including CLN5 disease. In addition, we detected abnormalities in the intracellular organelles and aberrations in neuronal sphingolipid transportation, verifying the previous findings obtained from Cln5-deficient mouse macrophages. Therefore, patient-derived iPSCs provide a suitable model to study the mechanisms of NCL diseases.

Australian Cattle Dogs with Neuronal Ceroid Lipofuscinosis are Homozygous for a CLN5 Nonsense Mutation Previously Identified in Border Collies

Background

Neuronal ceroid lipofuscinosis (NCL), a fatal neurodegenerative disease, has been diagnosed in young adult Australian Cattle Dogs.

Objective

Characterize the Australian Cattle Dog form of NCL and determine its molecular genetic cause.

Animals

Tissues from 4 Australian Cattle Dogs with NCL‐like signs and buccal swabs from both parents of a fifth affected breed member. Archived DNA samples from 712 individual dogs were genotyped.

Methods

Tissues were examined by fluorescence, electron, and immunohistochemical microscopy. A whole‐genome sequence was generated for 1 affected dog. A TaqMan allelic discrimination assay was used for genotyping.

Results

The accumulation of autofluorescent cytoplasmic storage material with characteristic ultrastructure in tissues from the 4 affected dogs supported a diagnosis of NCL. The whole‐genome sequence contained a homozygous nonsense mutation: CLN5:c.619C>T. All 4 DNA samples from clinically affected dogs tested homozygous for the variant allele. Both parents of the fifth affected dog were heterozygotes. Archived DNA samples from 346 Australian Cattle Dogs, 188 Border Collies, and 177 dogs of other breeds were homozygous for the reference allele. One archived Australian Cattle Dog sample was from a heterozygote.

Conclusions and Clinical Importance

The homozygous CLN5 nonsense is almost certainly causal because the same mutation previously had been reported to cause a similar form of NCL in Border Collies. Identification of the molecular genetic cause of Australian Cattle Dog NCL will allow the use of DNA tests to confirm the diagnosis of NCL in this breed.

Brain imaging in Kufs disease type B: case reports

Background

The clinical traits of Kufs disease (KD) type B (CLN13), an adult-onset neuronal ceroid lipofuscinosis (NCL), are well established according to the neurological features of the cases reported with mutations in CTSF.

The neuroradiological characteristics of this uncommon disease have not yet been outlined.

Case presentation

We hereby report the brain MRI features in two Caucasian women who carried homozygous mutations in CTSF, providing a short review of the neuroradiological findings of other common NCLs.

Together with a brain volume reduction, the two cases showed white matter hyperintensities and thinning of the corpus callosum at onset of the cognitive decline.

Conclusion

White matter hyperintensities associated with volume reduction of the corpus callosum may be present at the beginning of the behavioural changes in CLN13 and represent further clues for searching mutations in CTSF.

Golden Retriever dogs with neuronal ceroid lipofuscinosis have a two-base-pair deletion and frameshift in CLN5

We studied a recessive, progressive neurodegenerative disease occurring in Golden Retriever siblings with an onset of signs at 15 months of age. As the disease progressed these signs included ataxia, anxiety, pacing and circling, tremors, aggression, visual impairment and localized and generalized seizures. A whole genome sequence, generated with DNA from one affected dog, contained a plausibly causal homozygous mutation: CLN5:c.934_935delAG. This mutation was predicted to produce a frameshift and premature termination codon and encode a protein variant, CLN5:p.E312Vfs*6, which would lack 39 C-terminal amino acids. Eighteen DNA samples from the Golden Retriever family members were genotyped at CLN5:c.934_935delAG. Three clinically affected dogs were homozygous for the deletion allele; whereas, the clinically normal family members were either heterozygotes (n = 11) or homozygous for the reference allele (n = 4). Among archived Golden Retrievers DNA samples with incomplete clinical records that were also genotyped at the CLN5:c.934_935delAG variant, 1053 of 1062 were homozygous for the reference allele, 8 were heterozygotes and one was a deletion-allele homozygote. When contacted, the owner of this homozygote indicated that their dog had been euthanized because of a neurologic disease that progressed similarly to that of the affected Golden Retriever siblings. We have collected and stored semen from a heterozygous Golden Retriever, thereby preserving an opportunity for us or others to establish a colony of CLN5-deficient dogs.