Diagnostic tests for Niemann-Pick disease type C (NP-C): A critical review

Niemann-Pick disease type C (NP-C) is a neurovisceral lysosomal cholesterol trafficking and lipid storage disorder caused by mutations in one of the two genes, NPC1 or NPC2. Diagnosis has often been a difficult task, due to the wide range in age of onset of NP-C and clinical presentation of the disease, combined with the complexity of the cell biology (filipin) laboratory testing, even in combination with genetic testing. This has led to substantial delays in diagnosis, largely depending on the access to specialist centres and the level of knowledge about NP-C of the physician in the area. In recent years, advances in mass spectrometry has allowed identification of several sensitive plasma biomarkers elevated in NP-C (e.g. cholestane-3β,5α,6β-triol, lysosphingomyelin isoforms and bile acid metabolites), which, together with the concomitant progress in molecular genetic technology, have greatly impacted the strategy of laboratory testing. Specificity of the biomarkers is currently under investigation and other pathologies are being found to also result in elevations. Molecular genetic testing also has its limitations, notably with unidentified mutations and the classification of new variants. This review is intended to increase awareness on the currently available approaches to laboratory diagnosis of NP-C, to provide an up to date, comprehensive and critical evaluation of the various techniques (cell biology, biochemical biomarkers and molecular genetics), and to briefly discuss ongoing/future developments. The use of current tests in proper combination enables a rapid and correct diagnosis in a large majority of cases. However, even with recent progress, definitive diagnosis remains challenging in some patients, for whom combined genetic/biochemical/cytochemical markers do not provide a clear answer. Expertise and reference laboratories thus remain essential, and further work is still required to fulfill unmet needs

A novel mutation of AFG3L2 might cause dominant optic atrophy in patients with mild intellectual disability

Dominant optic neuropathies causing fiber loss in the optic nerve are among the most frequent inherited mitochondrial diseases. In most genetically resolved cases, the disease is associated to a mutation in OPA1, which encodes an inner mitochondrial dynamin involved in network fusion, cristae structure and mitochondrial genome maintenance. OPA1 cleavage is regulated by two m-AAA proteases, SPG7 and AFG3L2, which are, respectively involved in Spastic Paraplegia 7 and Spino-Cerebellar Ataxia 28. Here, we identified a novel mutation c.1402C>T in AFG3L2, modifying the arginine 468 in cysteine in an evolutionary highly conserved arginine-finger motif, in a family with optic atrophy and mild intellectual disability. Ophthalmic examinations disclosed a loss of retinal nerve fibers on the temporal and nasal sides of the optic disk and a red-green dyschromatopsia. Thus, our results suggest that neuro-ophthalmological symptom as optic atrophy might be associated with AFG3L2 mutations, and should prompt the screening of this gene in patients with isolated and syndromic inherited optic neuropathies

Ataxia with oculomotor apraxia type 2: clinical, biological and genotype/phenotype correlation study of a cohort of 90 patients

Ataxia with oculomotor apraxia type 2 (AOA2) is an autosomal recessive disease due to mutations in the senataxin gene, causing progressive cerebellar ataxia with peripheral neuropathy, cerebellar atrophy, occasional oculomotor apraxia and elevated alpha-feto-protein (AFP) serum level. We compiled a series of 67 previously reported and 58 novel ataxic patients who underwent senataxin gene sequencing because of suspected AOA2. An AOA2 diagnosis was established for 90 patients, originating from 15 countries worldwide, and 25 new senataxin gene mutations were found. In patients with AOA2, median AFP serum level was 31.0 mu g/l at diagnosis, which was higher than the median AFP level of AOA2 negative patients: 13.8 mu g/l, P = 0.0004; itself higher than the normal level (3.4 mu g/l, range from 0.5 to 17.2 mu g/l) because elevated AFP was one of the possible selection criteria. Polyneuropathy was found in 97.5% of AOA2 patients, cerebellar atrophy in 96%, occasional oculomotor apraxia in 51%, pyramidal signs in 20.5%, head tremor in 14%, dystonia in 13.5%, strabismus in 12.3% and chorea in 9.5%. No patient was lacking both peripheral neuropathy and cerebellar atrophy. The age at onset and presence of occasional oculomotor apraxia were negatively correlated to the progression rate of the disease (P = 0.03 and P = 0.009, respectively), whereas strabismus was positively correlated to the progression rate (P = 0.03). An increased AFP level as well as cerebellar atrophy seem to be stable in the course of the disease and to occur mostly at or before the onset of the disease. One of the two patients with a normal AFP level at diagnosis had high AFP levels 4 years later, while the other had borderline levels. The probability of missing AOA2 diagnosis, in case of sequencing senataxin gene only in non-Friedreich ataxia non-ataxia-telangiectasia ataxic patients with AFP level >= 7 mu g/l, is 0.23% and the probability for a non-Friedreich ataxia non-ataxia-telangiectasia ataxic patient to be affected with AOA2 with AFP levels >= 7 mu g/l is 46%. Therefore, selection of patients with an AFP level above 7 mu g/l for senataxin gene sequencing is a good strategy for AOA2 diagnosis. Pyramidal signs and dystonia were more frequent and disease was less severe with missense mutations in the helicase domain of senataxin gene than with missense mutations out of helicase domain and deletion and nonsense mutations (P = 0.001, P = 0.008 and P = 0.01, respectively). The lack of pyramidal signs in most patients may be explained by masking due to severe motor neuropathy

Gain-of-Function Mutation in Filamin A Potentiates Platelet Integrin αβ Activation

OBJECTIVE: Dominant mutations of the X-linked filamin A () gene are responsible for filaminopathies A, which are rare disorders including brain periventricular nodular heterotopia, congenital intestinal pseudo-obstruction, cardiac valves or skeleton malformations, and often macrothrombocytopenia. APPROACH AND RESULTS: We studied a male patient with periventricular nodular heterotopia and congenital intestinal pseudo-obstruction, his unique X-linked allele carrying a stop codon mutation resulting in a 100-amino acid-long FLNa C-terminal extension (NP_001447.2: ). Platelet counts were normal, with few enlarged platelets. FLNa was detectable in all platelets but at 30% of control levels. Surprisingly, all platelet functions were significantly upregulated, including platelet aggregation and secretion, as induced by ADP, collagen, or von Willebrand factor in the presence of ristocetin, as well as thrombus formation in blood flow on a collagen or on a von Willebrand factor matrix. Most importantly, patient platelets stimulated with ADP exhibited a marked increase in αβ integrin activation and a parallel increase in talin recruitment to β, contrasting with normal Rap1 activation. These results are consistent with the mutant FLNa affecting the last step of αβ activation. Overexpression of mutant FLNa in the HEL megakaryocytic cell line correlated with an increase (compared with wild-type FLNa) in PMA-induced fibrinogen binding to and in talin and kindlin-3 recruitment by αβ. CONCLUSIONS: Altogether, our results are consistent with a less binding of mutant FLNa to β and the facilitated recruitment of talin by β on platelet stimulation, explaining the increased αβ activation and the ensuing gain-of-platelet functions

Effectiveness of anti-psychotics and related drugs in the Huntington French-speaking group cohort.

PURPOSE: Huntington's disease is a rare condition. Patients are commonly treated with antipsychotics and tetrabenazine. The evidence of their effect on disease progression is limited and no comparative study between these drugs has been conducted. We therefore compared the effectiveness of antipsychotics on disease progression. METHODS: 956 patients from the Huntington French Speaking Group were followed for up to 8 years between 2002 and 2010. The effectiveness of treatments was assessed using Unified Huntington's Disease Rating Scale (UHDRS) scores and then compared using a mixed model adjusted on a multiple propensity score. RESULTS: 63% of patients were treated with antipsychotics during the survey period. The most commonly prescribed medications were dibenzodiazepines (38%), risperidone (13%), tetrabenazine (12%) and benzamides (12%). There was no difference between treatments on the motor and behavioural declines observed, after taking the patient profiles at the start of the drug prescription into account. In contrast, the functional decline was lower in the dibenzodiazepine group than the other antipsychotic groups (Total Functional Capacity: 0.41 ± 0.17 units per year vs. risperidone and 0.54 ± 0.19 vs. tetrabenazine, both p<0.05). Benzamides were less effective than other antipsychotics on cognitive evolution (Stroop interference, Stroop color and Literal fluency: p<0.05). CONCLUSIONS: Antipsychotics are widely used to treat patients with Huntington's disease. Although differences in motor or behavioural profiles between patients according to the antipsychotics used were small, there were differences in drug effectiveness on the evolution of functional and cognitive scores

Pathogenic variants in the AFG3L2 proteolytic domain cause SCA28 through haploinsufficiency and proteostatic stress-driven OMA1 activation

Background: Spinocerebellar ataxia type 28 (SCA28) is a dominantly inherited neurodegenerative disease caused by pathogenic variants in AFG3L2. The AFG3L2 protein is a subunit of mitochondrial m-AAA complexes involved in protein quality control. Objective of this study was to determine the molecular mechanisms of SCA28, which has eluded characterisation to date. Methods: We derived SCA28 patient fibroblasts carrying different pathogenic variants in the AFG3L2 proteolytic domain (missense: the newly identified p.F664S and p.M666T, p.G671R, p.Y689H and a truncating frameshift p.L556fs) and analysed multiple aspects of mitochondrial physiology. As reference of residual m-AAA activity, we included SPAX5 patient fibroblasts with homozygous p.Y616C pathogenic variant, AFG3L2 +/\ue2 ' HEK293 T cells by CRISPR/Cas9-genome editing and Afg3l2 \ue2 '/\ue2 ' murine fibroblasts. Results: We found that SCA28 cells carrying missense changes have normal levels of assembled m-AAA complexes, while the cells with a truncating pathogenic variant had only half of this amount. We disclosed inefficient mitochondrial fusion in SCA28 cells caused by increased OPA1 processing operated by hyperactivated OMA1. Notably, we found altered mitochondrial proteostasis to be the trigger of OMA1 activation in SCA28 cells, with pharmacological attenuation of mitochondrial protein synthesis resulting in stabilised levels of OMA1 and OPA1 long forms, which rescued mitochondrial fusion efficiency. Secondary to altered mitochondrial morphology, mitochondrial calcium uptake resulted decreased in SCA28 cells. Conclusion: Our data identify the earliest events in SCA28 pathogenesis and open new perspectives for therapy. By identifying similar mitochondrial phenotypes between SCA28 cells and AFG3L2 +/- cells, our results support haploinsufficiency as the mechanism for the studied pathogenic variants

Clin Case Rep

The early onset of gait akinesia should not rule out the diagnosis of hereditary chorea. It would be helpful to proceed to a whole‐genome and long‐read sequencing in order to track a new pathogenic variant including noncoding repeat expansion

Follow-up nationwide survey on predictive genetic testing for late-onset hereditary neurological diseases in Japan

A follow-up nationwide survey on predictive genetic testing for late-onset neurological diseases in Japan was conducted. A questionnaire was sent to 89 institutional members of the Japan's National Liaison Council for Clinical Sections of Medical Genetics, and was returned by 60 (67.4%). A total of 301 clients with an interest in predictive testing were accumulated from April 2006 to March 2011. The greatest interest was shown for spinocerebellar degeneration (SCD, n = 110), followed by myotonic dystrophy type 1 (DM1, n = 69), Huntington's disease (HD, n = 52) and familial amyloid polyneuropathy (FAP, n = 35). The ratios of clients who actually underwent predictive testing were: SCD, 21.8%; DM1, 39.1%; HD, 26.9%; and FAP, 74.3%, indicating that predictive testing was conducted very cautiously for untreatable neurological diseases in Japan. Clinical geneticists were predominantly involved in genetic counseling, whereas the participation of non-medical doctor (non-MD) staff, including nurses, clinical psychologists and genetic counselors, was not common. Lack of non-MD counseling staff was one of the most serious issues in conducting predictive testing, which has not been improved since the previous survey performed in 2006. Institutional arrangements, such as revision of medical insurance system regarding genetic testing and counseling, might be necessary to resolve this issue.ArticleJOURNAL OF HUMAN GENETICS. 58(8):560-563 (2013)journal articl

Hereditary optic neuropathies share a common mitochondrial coupling defect

Hereditary optic neuropathies are heterogeneous diseases characterized by the degeneration of retinal ganglion cells leading to optic nerve atrophy and impairment of central vision. We found a common coupling defect of oxidative phosphorylation in fibroblasts of patients affected by autosomal dominant optic atrophy (mutations of OPA1), autosomal dominant optic atrophy associated with cataract (mutations of OPA3), and Leber\u27s hereditary optic neuropathy, a disorder associated with point mutations of mitochondrial DNA complex I genes. Interestingly, the energetic defect was significantly more pronounced in Leber\u27s hereditary optic neuropathy and autosomal dominant optic atrophy patients with a more complex phenotype, the so-called plus phenotype. Ann Neurol 200

KCNQ2 R144 variants cause neurodevelopmental disability with language impairment and autistic features without neonatal seizures through a gain-of-function mechanism

Prior studies have revealed remarkable phenotypic heterogeneity in KCNQ2-related disorders, correlated with effects on biophysical features of heterologously expressed channels. Here, we assessed phenotypes and functional properties associated with KCNQ2 missense variants R144W, R144Q, and R144G. We also explored in vitro blockade of channels carrying R144Q mutant subunits by amitriptyline