A postzygotic de novo NCDN mutation identified in a sporadic FTLD patient results in neurochondrin haploinsufficiency and altered FUS granule dynamics.

Frontotemporal dementia (FTD) is a heterogeneous clinical disorder characterized by progressive abnormalities in behavior, executive functions, personality, language and/or motricity. A neuropathological subtype of FTD, frontotemporal lobar degeneration (FTLD)-FET, is characterized by protein aggregates consisting of the RNA-binding protein fused in sarcoma (FUS). The cause of FTLD-FET is not well understood and there is a lack of genetic evidence to aid in the investigation of mechanisms of the disease. The goal of this study was to identify genetic variants contributing to FTLD-FET and to investigate their effects on FUS pathology. We performed whole-exome sequencing on a 50-year-old FTLD patient with ubiquitin and FUS-positive neuronal inclusions and unaffected parents, and identified a de novo postzygotic nonsense variant in the NCDN gene encoding Neurochondrin (NCDN), NM_014284.3:c.1206G > A, p.(Trp402*). The variant was associated with a ~ 31% reduction in full-length protein levels in the patient's brain, suggesting that this mutation leads to NCDN haploinsufficiency. We examined the effects of NCDN haploinsufficiency on FUS and found that depleting primary cortical neurons of NCDN causes a reduction in the total number of FUS-positive cytoplasmic granules. Moreover, we found that these granules were significantly larger and more highly enriched with FUS. We then examined the effects of a loss of FUS function on NCDN in neurons and found that depleting cells of FUS leads to a decrease in NCDN protein and mRNA levels. Our study identifies the NCDN protein as a likely contributor of FTLD-FET pathophysiology. Moreover, we provide evidence for a negative feedback loop of toxicity between NCDN and FUS, where loss of NCDN alters FUS cytoplasmic dynamics, which in turn has an impact on NCDN expression.

Early-Onset Cerebral Amyloid Angiopathy and Alzheimer Disease Related to an APP Locus Triplication.

BACKGROUND AND OBJECTIVE: To report a triplication of the amyloid-ß precursor protein (APP) locus along with relative messenger RNA (mRNA) expression in a family with autosomal dominant early-onset cerebral amyloid angiopathy (CAA) and Alzheimer disease (AD). METHODS: Four copies of the APP gene were identified by quantitative multiplex PCR of short fluorescent fragments, fluorescent in situ hybridization (FISH), and array comparative genomic hybridization. APP mRNA levels were assessed using reverse-transcription-digital droplet PCR in the proband's whole blood and compared with 10 controls and 9 APP duplication carriers. RESULTS: Beginning at age 39 years, the proband developed severe episodic memory deficits with a CSF biomarker profile typical of AD and multiple lobar microbleeds in the posterior regions on brain MRI. His father had seizures and recurrent cerebral hemorrhage since the age of 37 years. His cerebral biopsy showed abundant perivascular amyloid deposits, leading to a diagnosis of CAA. In the proband, we identified 4 copies of a 506-kb region located on chromosome 21q21.3 and encompassing the whole APP gene without any other gene. FISH suggested that the genotype of the proband was 3 copies/1 copy corresponding to an APP locus triplication, which was consistent with the presence of 2 APP copies in the healthy mother and with the paternal medical history. Analysis of the APP mRNA level showed a 2-fold increase in the proband and a 1.8 fold increase in APP duplication carriers compared with controls. DISCUSSION: Increased copy number of APP is sufficient to cause AD and CAA, with likely earlier onset in case of triplication compared with duplication.

Biallelic MYORG mutation carriers exhibit primary brain calcification with a distinct phenotype.

Primary familial brain calcification (PFBC) is a rare neurogenetic disorder with diverse neuropsychiatric expression. Mutations in four genes cause autosomal dominant PFBC: SLC20A2, XPR1, PDGFB and PDGFRB. Recently, biallelic mutations in the MYORG gene have been reported to cause PFBC with an autosomal recessive pattern of inheritance. We screened MYORG in 29 unrelated probands negatively screened for the autosomal dominant PFBC genes and identified 11 families with a biallelic rare or novel predicted damaging variant. We studied the clinical and radiological features of 16 patients of these 11 families and compared them to that of 102 autosomal dominant PFBC patients carrying a mutation in one of the four known autosomal dominant PFBC genes. We found that MYORG patients exhibited a high clinical penetrance with a median age of onset of 52 years (range: 21-62) with motor impairment at the forefront. In particular, dysarthria was the presenting sign in 11/16 patients. In contrast to patients with autosomal dominant PFBC, 12/15 (80%) symptomatic patients eventually presented at least four of the following five symptoms: dysarthria, cerebellar syndrome, gait disorder of any origin, akinetic-hypertonic syndrome and pyramidal signs. In addition to the most severe clinical pattern, MYORG patients exhibited the most severe pattern of calcifications as compared to the patients from the four autosomal dominant PFBC gene categories. Strikingly, 12/15 presented with brainstem calcifications in addition to extensive calcifications in other brain areas (lenticular nuclei, thalamus, cerebellar hemispheres, vermis, ±cortex). Among them, eight patients exhibited pontine calcifications, which were observed in none of the autosomal dominant PFBC patients and hence appeared to be highly specific. Finally, all patients exhibited cerebellar atrophy with diverse degrees of severity on CT scans. We confirmed the existence of cerebellar atrophy by performing MRI voxel-based morphometry analyses of MYORG patients with autosomal dominant PFBC mutation carriers as a comparison group. Of note, in three families, the father carried small pallido-dentate calcifications while carrying the mutation at the heterozygous state, suggesting a putative phenotypic expression in some heterozygous carriers. In conclusion, we confirm that MYORG is a novel major PFBC causative gene and that the phenotype associated with such mutations may be recognized based on pedigree, clinical and radiological features.

APP Mutations in Cerebral Amyloid Angiopathy with or without Cortical Calcifications: Report of Three Families and a Literature Review.

BACKGROUND: Specific APP mutations cause cerebral amyloid angiopathy (CAA) with or without Alzheimer's disease (AD). OBJECTIVE: We aimed at reporting APP mutations associated with CAA, describe the clinical, cerebrospinal fluid AD biomarkers, and neuroimaging features, and compare them with the data from the literature. METHODS: We performed a retrospective study in two French genetics laboratories by gathering all clinical and neuroimaging data from patients referred for a genetic diagnosis of CAA with an age of onset before 66 years and fulfilling the other Boston revised criteria. We studied the segregation of mutations in families and performed a comprehensive literature review of all cases reported with the same APP mutation. RESULTS: We screened APP in 61 unrelated French patients. Three mutations, located in the Aß coding region, were detected in five patients from three families: p.Ala692Gly (Flemish), p.Glu693Lys (Italian), and p.Asp694Asn (Iowa). Patients exhibited CAA and progressive cognitive impairment associated with cortical calcifications in the Iowa and Italian mutation carriers, but not the patient carrying the Flemish mutation. CONCLUSIONS: This is the first evidence of cortical calcification in patients with an APP mutation other than the Iowa mutation. We discuss the radiological, cerebrospinal fluid, and clinical phenotype of patients carrying these mutations in the literature.

A de novo nonsense PDGFB mutation causing idiopathic basal ganglia calcification with laryngeal dystonia.

Idiopathic basal ganglia calcification (IBGC) is characterized by brain calcification and a wide variety of neurologic and psychiatric symptoms. In families with autosomal dominant inheritance, three causative genes have been identified: SLC20A2, PDGFRB, and, very recently, PDGFB. Whereas in clinical practice sporadic presentation of IBGC is frequent, well-documented reports of true sporadic occurrence are rare. We report the case of a 20-year-old woman who presented laryngeal dystonia revealing IBGC. Her healthy parents' CT scans were both normal. We identified in the proband a new nonsense mutation in exon 4 of PDGFB, c.439C>T (p.Gln147*), which was absent from the parents' DNA. This mutation may result in a loss-of-function of PDGF-B, which has been shown to cause IBGC in humans and to disrupt the blood-brain barrier in mice, resulting in brain calcification. The c.439C>T mutation is located between two previously reported nonsense mutations, c.433C>T (p.Gln145*) and c.445C>T (p.Arg149*), on a region that could be a hot spot for de novo mutations. We present the first full demonstration of the de novo occurrence of an IBGC-causative mutation in a sporadic case.

Phenotypic spectrum of probable and genetically-confirmed idiopathic basal ganglia calcification.

Idiopathic basal ganglia calcification is characterized by mineral deposits in the brain, an autosomal dominant pattern of inheritance in most cases and genetic heterogeneity. The first causal genes, SLC20A2 and PDGFRB, have recently been reported. Diagnosing idiopathic basal ganglia calcification necessitates the exclusion of other causes, including calcification related to normal ageing, for which no normative data exist. Our objectives were to diagnose accurately and then describe the clinical and radiological characteristics of idiopathic basal ganglia calcification. First, calcifications were evaluated using a visual rating scale on the computerized tomography scans of 600 consecutively hospitalized unselected controls. We determined an age-specific threshold in these control computerized tomography scans as the value of the 99th percentile of the total calcification score within three age categories: <40, 40-60, and >60 years. To study the phenotype of the disease, patients with basal ganglia calcification were recruited from several medical centres. Calcifications that rated below the age-specific threshold using the same scale were excluded, as were patients with differential diagnoses of idiopathic basal ganglia calcification, after an extensive aetiological assessment. Sanger sequencing of SLC20A2 and PDGFRB was performed. In total, 72 patients were diagnosed with idiopathic basal ganglia calcification, 25 of whom bore a mutation in either SLC20A2 (two families, four sporadic cases) or PDGFRB (one family, two sporadic cases). Five mutations were novel. Seventy-one per cent of the patients with idiopathic basal ganglia calcification were symptomatic (mean age of clinical onset: 39 ± 20 years; mean age at last evaluation: 55 ± 19 years). Among them, the most frequent signs were: cognitive impairment (58.8%), psychiatric symptoms (56.9%) and movement disorders (54.9%). Few clinical differences appeared between SLC20A2 and PDGFRB mutation carriers. Radiological analysis revealed that the total calcification scores correlated positively with age in controls and patients, but increased more rapidly with age in patients. The expected total calcification score was greater in SLC20A2 than PDGFRB mutation carriers, beyond the effect of the age alone. No patient with a PDGFRB mutation exhibited a cortical or a vermis calcification. The total calcification score was more severe in symptomatic versus asymptomatic individuals. We provide the first phenotypical description of a case series of patients with idiopathic basal ganglia calcification since the identification of the first causative genes. Clinical and radiological diversity is confirmed, whatever the genetic status. Quantification of calcification is correlated with the symptomatic status, but the location and the severity of the calcifications don't reflect the whole clinical diversity. Other biomarkers may be helpful in better predicting clinical expression.

Mutation of the PDGFRB gene as a cause of idiopathic basal ganglia calcification.

OBJECTIVES: To identify a new idiopathic basal ganglia calcification (IBGC)-causing gene. METHODS: In a 3-generation family with no SLC20A2 mutation, we performed whole exome sequencing in 2 affected first cousins, once removed. Nonsynonymous coding variants, splice acceptor and donor site variants, and frameshift coding indels (NS/SS/I) were filtered against dbSNP131, the HapMap Project, 1000 Genomes Project, and our in-house database including 72 exomes. RESULTS: Seventeen genes were affected by identical unknown NS/SS/I variations in the 2 patients. After screening the relatives, the p.Leu658Pro substitution within the PDGFRB gene remained the sole unknown mutation segregating with the disease in the family. This variation, which is predicted to be highly damaging, was present in 13 of 13 affected subjects and absent in 8 relatives without calcifications. Sequencing PDGFRB of 19 other unrelated IBGC cases allowed us to detect another potentially pathogenic substitution within PDGFRB, p.Arg987Trp, also predicted to be highly damaging. PDGFRB encodes a protein involved in angiogenesis and in the regulation of inorganic phosphate (Pi) transport in vascular smooth muscle cells via Pit-1, a Pi transporter encoded by SLC20A1. CONCLUSION: Mutations of PDGFRB further support the involvement of this biological pathway in IBGC pathophysiology.

Expression of p53 family members and CD44 in oral squamous cell carcinoma (OSCC) in relation to tumorigenesis.

Oral squamous cell carcinomas (OSCCs) are described as the result of a multistep tumorigenesis process. In order to develop useful diagnosis of pre-malignant lesions, expression of p53 family members and the cancer stem cell (CSCs) marker, CD44v6, were studied in histologically normal oral epithelium, precancerous lesions and succeeding invasive OSCCs. p53 was expressed focally in normal epithelium adjacent to tumors, while expression was high in intra-epithelial neoplasia and moderate in OSCC. p63 nuclear staining was important in basal and suprabasal layers of histologically normal oral mucosa and in immature compartments of premalignant lesions and cancer. In epithelium without neoplasia, intense p73 staining was observed in the basal layer, while focal expression was present in suprabasal layers. Most immature dysplastic areas showed either high or moderate staining, whereas those in OSCCs expressed low and moderate p73 level expression. CD44v6 was only expressed in poorly differentiated areas of epithelium, altered or not. p53, p63 and p73 positive stainings were statistically related in intra-epithelial neoplasia to tumours. Analysis of TP53 mutations in 17% of tumours principally revealed G>A and A>G transitions. No relation was observed between this mutational profile and different immunostainings. In conclusion, our results support that immunostaining of p53 family members might be helpful in diagnosis and monitoring of high-risk pre-malignant lesions of oral epithelium. The combination of staining patterns of p63, p73alpha and CD44v6 enabled us to isolate phenotypic undifferentiated or transient amplifying areas, reflecting the immaturity of the tumour cell lineage. While CD44v6 expression is an interesting marker of such epithelial cells, it is not specific enough to be useful alone and other phenotypic markers are needed.

Disease progression despite early loss of polyglutamine protein expression in SCA7 mouse model.

Nine neurodegenerative diseases including Huntington's disease (HD) and spinocerebellar ataxia type 7 (SCA7) are caused by an expansion of a polyglutamine (polyQ) stretch in the respective proteins. Aggregation of expanded polyQ-containing proteins into the nucleus is a hallmark of these diseases. Recent evidence indicates that transcriptional dysregulation may contribute to the molecular pathogenesis of these diseases. Using SCA7 and HD mouse models in which we recently described a retinal phenotype, we investigated whether altered gene expression underlies photoreceptor dysfunction. In both models, rhodopsin promoter activity was early and dramatically repressed, suggesting that downregulation of photoreceptor-specific genes plays a major role in polyQ-induced retinal dysfunction. Because the rhodopsin promoter drives mutant ataxin-7 expression in our SCA7 mice, we also assessed whether downregulation of mutant SCA7 transgene would reverse retinopathy progression and aggregate formation. Although residual expression of mutant ataxin-7 was found negligible from 9 weeks of age, SCA7 transgenic mice showed a progressive decline of photoreceptor activity leading to a complete loss of electroretinographic responses from 1 year of age. At this age, aggregates were cleared in only half of the photoreceptors, indicating that their formation is not fully reversible in this model. We demonstrate here that abolishing full-length mutant ataxin-7 expression did not reverse retinopathy progression in SCA7 mice, raising the possibility that some polyQ-induced pathological events might be irreversible.