KCTD7 deficiency defines a distinct neurodegenerative disorder with a conserved autophagy-lysosome defect.

OBJECTIVE: Several small case series identified KCTD7 mutations in patients with a rare autosomal recessive disorder designated progressive myoclonic epilepsy (EPM3) and neuronal ceroid lipofuscinosis (CLN14). Despite the name KCTD (potassium channel tetramerization domain), KCTD protein family members lack predicted channel domains. We sought to translate insight gained from yeast studies to uncover disease mechanisms associated with deficiencies in KCTD7 of unknown function. METHODS: Novel KCTD7 variants in new and published patients were assessed for disease causality using genetic analyses, cell-based functional assays of patient fibroblasts and knockout yeast, and electron microscopy of patient samples. RESULTS: Patients with KCTD7 mutations can exhibit movement disorders or developmental regression before seizure onset, and are distinguished from similar disorders by an earlier age of onset. Although most published KCTD7 patient variants were excluded from a genome sequence database of normal human variations, most newly identified patient variants are present in this database, potentially challenging disease causality. However, genetic analysis and impaired biochemical interactions with cullin 3 support a causal role for patient KCTD7 variants, suggesting deleterious alleles of KCTD7 and other rare disease variants may be underestimated. Both patient-derived fibroblasts and yeast lacking Whi2 with sequence similarity to KCTD7 have impaired autophagy consistent with brain pathology. INTERPRETATION: Biallelic KCTD7 mutations define a neurodegenerative disorder with lipofuscin and lipid droplet accumulation but without defining features of neuronal ceroid lipofuscinosis or lysosomal storage disorders. KCTD7 deficiency appears to cause an underlying autophagy-lysosome defect conserved in yeast, thereby assigning a biological role for KCTD7. Ann Neurol 2018;84:774-788.

Detailed Clinical Phenotype and Molecular Genetic Findings in CLN3-Associated Isolated Retinal Degeneration.

Importance: Mutations in genes traditionally associated with syndromic retinal disease are increasingly found to cause nonsyndromic inherited retinal degenerations. Mutations in CLN3 are classically associated with juvenile neuronal ceroid lipofuscinosis, a rare neurodegenerative disease with early retinal degeneration and progressive neurologic deterioration, but have recently also been identified in patients with nonsyndromic inherited retinal degenerations. To our knowledge, detailed clinical characterization of such cases has yet to be reported. Objective: To provide detailed clinical, electrophysiologic, structural, and molecular genetic findings in nonsyndromic inherited retinal degenerations associated with CLN3 mutations. Design, Setting, and Participants: A multi-institutional case series of 10 patients who presented with isolated nonsyndromic retinal disease and mutations in CLN3. Patient ages ranged from 16 to 70 years; duration of follow-up ranged from 3 to 29 years. Main Outcomes and Measures: Longitudinal clinical evaluation, including full ophthalmic examination, multimodal retinal imaging, perimetry, and electrophysiology. Molecular analyses were performed using whole-genome sequencing or whole-exome sequencing. Electron microscopy studies of peripheral lymphocytes and CLN3 transcript analysis with polymerase chain reaction amplification were performed in a subset of patients. Results: There were 7 females and 3 males in this case series, with a mean (range) age at last review of 37.1 (16-70) years. Of the 10 patients, 4 had a progressive late-onset rod-cone dystrophy, with a mean (range) age at onset of 29.7 (20-40) years, and 6 had an earlier onset rod-cone dystrophy, with a mean (range) age at onset of 12.1 (7-17) years. Ophthalmoscopic examination features included macular edema, mild intraretinal pigment migration, and widespread atrophy in advanced disease. Optical coherence tomography imaging demonstrated significant photoreceptor loss except in patients with late-onset disease who had a focal preservation of the ellipsoid zone and outer nuclear layer in the fovea. Electroretinography revealed a rod-cone pattern of dysfunction in 6 patients and were completely undetectable in 2 patients. Six novel CLN3 variants were identified in molecular analyses. Conclusions and Relevance: This report describes detailed clinical, imaging, and genetic features of CLN3-associated nonsyndromic retinal degeneration. The age at onset and natural progression of retinal disease differs greatly between syndromic and nonsyndromic CLN3 disease, which may be associated with genotypic differences.

Diagnosis and misdiagnosis of adult neuronal ceroid lipofuscinosis (Kufs disease).

OBJECTIVE: To critically re-evaluate cases diagnosed as adult neuronal ceroid lipofuscinosis (ANCL) in order to aid clinicopathologic diagnosis as a route to further gene discovery. METHODS: Through establishment of an international consortium we pooled 47 unsolved cases regarded by referring centers as ANCL. Clinical and neuropathologic experts within the Consortium established diagnostic criteria for ANCL based on the literature to assess each case. A panel of 3 neuropathologists independently reviewed source pathologic data. Cases were given a final clinicopathologic classification of definite ANCL, probable ANCL, possible ANCL, or not ANCL. RESULTS: Of the 47 cases, only 16 fulfilled the Consortium's criteria of ANCL (5 definite, 2 probable, 9 possible). Definitive alternate diagnoses were made in 10, including Huntington disease, early-onset Alzheimer disease, Niemann-Pick disease, neuroserpinopathy, prion disease, and neurodegeneration with brain iron accumulation. Six cases had features suggesting an alternate diagnosis, but no specific condition was identified; in 15, the data were inadequate for classification. Misinterpretation of normal lipofuscin as abnormal storage material was the commonest cause of misdiagnosis. CONCLUSIONS: Diagnosis of ANCL remains challenging; expert pathologic analysis and recent molecular genetic advances revealed misdiagnoses in >1/3 of cases. We now have a refined group of cases that will facilitate identification of new causative genes.

The Chihuahua dog: A new animal model for neuronal ceroid lipofuscinosis CLN7 disease?

Neuronal ceroid lipofuscinoses (NCLs) are a group of incurable lysosomal storage disorders characterized by neurodegeneration and accumulation of lipopigments mainly within the neurons. We studied two littermate Chihuahua dogs presenting with progressive signs of blindness, ataxia, pacing, and cognitive impairment from 1 year of age. Because of worsening of clinical signs, both dogs were euthanized at about 2 years of age. Postmortem examination revealed marked accumulation of autofluorescent intracellular inclusions within the brain, characteristic of NCL. Whole-genome sequencing was performed on one of the affected dogs. After sequence alignment and variant calling against the canine reference genome, variants were identified in the coding region or splicing regions of four previously known NCL genes (CLN6, ARSG, CLN2 [=TPP1], and CLN7 [=MFSD8]). Subsequent segregation analysis within the family (two affected dogs, both parents, and three relatives) identified MFSD8:p.Phe282Leufs13*, which had previously been identified in one Chinese crested dog with no available ancestries, as the causal mutation. Because of the similarities of the clinical signs and histopathological changes with the human form of the disease, we propose that the Chihuahua dog could be a good animal model of CLN7 disease.

mTOR-dependent abnormalities in autophagy characterize human malformations of cortical development: evidence from focal cortical dysplasia and tuberous sclerosis.

Focal cortical dysplasia (FCD) is a localized malformation of cortical development and is the commonest cause of severe childhood epilepsy in surgical practice. Children with FCD are severely disabled by their epilepsy, presenting with frequent seizures early in life. The commonest form of FCD in children is characterized by the presence of an abnormal population of cells, known as balloon cells. Similar pathological changes are seen in the cortical malformations that characterize patients with tuberous sclerosis complex (TSC). However, the cellular and molecular mechanisms that underlie the malformations of FCD and TSC are not well understood. We provide evidence for a defect in autophagy in FCD and TSC. We have found that balloon cells contain vacuoles that include components of the autophagy pathway. Specifically, we show that balloon cells contain prominent lysosomes by electron microscopy, immunohistochemistry for LAMP1 and LAMP2, LysoTracker labelling and enzyme histochemistry for acid phosphatase. Furthermore, we found that balloon cells contain components of the ATG pathway and that there is cytoplasmic accumulation of the regulator of autophagy, DOR. Most importantly we found that there is abnormal accumulation of the autophagy cargo protein, p62. We show that this defect in autophagy can be, in part, reversed in vitro by inhibition of the mammalian target of rapamycin (mTOR) suggesting that abnormal activation of mTOR may contribute directly to a defect in autophagy in FCD and TSC.

Human pathology in NCL.

In childhood the neuronal ceroid lipofuscinoses (NCL) are the most frequent lysosomal diseases and the most frequent neurodegenerative diseases but, in adulthood, they represent a small fraction among the neurodegenerative diseases. Their morphology is marked by: (i) loss of neurons, foremost in the cerebral and cerebellar cortices resulting in cerebral and cerebellar atrophy; (ii) an almost ubiquitous accumulation of lipopigments in nerve cells, but also in extracerebral tissues. Loss of cortical neurons is selective, indiscriminate depletion in early childhood forms occurring only at an advanced stage, whereas loss of neurons in subcortical grey-matter regions has not been quantitatively documented. Among the fourteen different forms of NCL described to date, CLN1 and CLN10 are marked by granular lipopigments, CLN2 by curvilinear profiles (CVPs), CLN3 by fingerprint profiles (FPPs), and other forms by a combination of these features. Among extracerebral tissues, lymphocytes, skin, rectum, skeletal muscle and, occasionally, conjunctiva are possible guiding targets for diagnostic identification, the precise type of NCL then requiring molecular analysis within the clinical and morphological context. Autosomal-recessive adult NCL has been linked molecularly to different childhood forms, i.e. CLN1, CLN5, and CLN6, whilst autosomal-dominant adult NCL, now designated as CLN4, is caused by a newly identified separate gene, DNAJC5. This article is part of a Special Issue entitled: The Neuronal Ceroid Lipofuscinoses or Batten Disease.