Glycan-independent role of calnexin in the intracellular retention of Charcot-Marie-tooth 1A Gas3/PMP22 mutants

Missense point mutations in Gas3/PMP22 are responsible for the peripheral neuropathies Charcot-Marie-Tooth 1A and Dejerine Sottas syndrome. These mutations induce protein misfolding with the consequent accumulation of the proteins in the endoplasmic reticulum and the formation of aggresomes. During folding, Gas3/PMP22 associates with the lectin chaperone calnexin. Here, we show that calnexin interacts with the misfolded transmembrane domains of Gas3/PMP22, fused to green fluorescent protein, in a glycan-independent manner. In addition, photobleaching experiments in living cells revealed that Gas3/PMP22-green fluorescent protein mutants are mobile but diffuse at almost half the diffusion coefficient of wild type protein. Our results support emerging models for a glycan-independent chaperone role for calnexin and for the mechanism of retention of misfolded membrane proteins in the endoplasmic reticulum

Rare among rare: phenotypes of uncommon CMT genotypes

(1) Background: Charcot-Marie-Tooth disease (CMT) is the most frequent form of inherited chronic motor and sensory polyneuropathy. Over 100 CMT causative genes have been identified. Previous reports found PMP22, GJB1, MPZ, and MFN2 as the most frequently involved genes. Other genes, such as BSCL2, MORC2, HINT1, LITAF, GARS, and autosomal dominant GDAP1 are responsible for only a minority of CMT cases. (2) Methods: we present here our records of CMT patients harboring a mutation in one of these rare genes (BSCL2, MORC2, HINT1, LITAF, GARS, autosomal dominant GDAP1). We studied 17 patients from 8 unrelated families. All subjects underwent neurologic evaluation and genetic testing by next-generation sequencing on an Ion Torrent PGM (Thermo Fischer) with a 44-gene custom panel. (3) Results: the following variants were found: BSCL2 c.263A > G p.Asn88Ser (eight subjects), MORC2 c.1503A > T p.Gln501His (one subject), HINT1 c.110G > C p.Arg37Pro (one subject), LITAF c.404C > G p.Pro135Arg (two subjects), GARS c.1660G > A p.Asp554Asn (three subjects), GDAP1 c.374G > A p.Arg125Gln (two subjects). (4) Expanding the spectrum of CMT phenotypes is of high relevance, especially for less common variants that have a higher risk of remaining undiagnosed. The necessity of reaching a genetic definition for most patients is great, potentially making them eligible for future experimentations

Clinical and pathology characterization of small nerve fiber neuro(no)pathy in cerebellar ataxia with neuropathy and vestibular areflexia syndrome

Background and purpose; Biallelic mutation/expansion of the gene RFC1 has been described in association with a spectrum of manifestations ranging from isolated sensory neuro(no)pathy to a complex presentation as cerebellar ataxia with neuropathy and vestibular areflexia syndrome (CANVAS). Our aim was to define the frequency and characteristics of small fiber neuropathy (SFN) in RFC1 disease at different stages.Methods: RFC1 cases were screened for SFN using the Neuropathic Pain Symptom Inventory and Composite Autonomic Symptom Score 31 questionnaires. Clinical data were retrospectively collected. If available, lower limb skin biopsy samples were evaluated for somatic epidermal and autonomic subepidermal structure innervation and compared to healthy controls (HCs).Results: Forty patients, median age at onset 54 years (interquartile range [IQR] 49-61) and disease duration 10 years (IQR 6-16), were enrolled. Mild-to-moderate positive symptoms (median Neuropathic Pain Symptom Inventory score 12.1/50, IQR 5.5-22.3) and relevant autonomic disturbances (median Composite Autonomic Symptom Score 31 37.0/100, IQR 17.7-44.3) were frequently reported and showed scarce correlation with disease duration. A non-length-dependent impairment in nociception was evident in both clinical and paraclinical investigations. An extreme somatic denervation was observed in all patients at both proximal (fibers/mm, RFC1 cases 0.0 vs. HCs 20.5, p < 0.0001) and distal sites (fibers/mm, RFC1 cases 0.0 vs. HCs 13.1, p < 0.0001); instead only a slight decrease was observed in cholinergic and adrenergic innervation of autonomic structures.Conclusions: RFC1 disease is characterized by a severe and widespread somatic SFN. Skin denervation may potentially represent the earliest feature and drive towards the suspicion of this disorder

A CD21 low phenotype, with no evidence of autoantibodies to complement proteins, is consistent with a poor prognosis in CLL.

B-cell chronic lymphocytic leukemia (CLL) is characterized by differential BCR signaling and autoimmune complications. Complement modulates B-cell function via C3d and CD21 cross-linked to the B-cell receptor (BCR). We hypothesized that CD21 contributes to BCR signaling and participates in the autoimmunity associated with CLL. We analyzed CD21 expression on 106 CLL patient samples and matched serum from 50 patients for the presence of soluble CD21 and autoantibodies to CR2, CR1, MCP and FH. CD21 expression on CLL B-cells was significantly lower than that expressed on B-cells from age-matched controls (P < 0.0001) and was inversely correlated with soluble CD21 (r2 = –0.41). We found no evidence of autoantibody to any complement regulator. Low CD21 expression correlated to prognostic subsets of CLL patients, i.e. cases with unmutated IGHV genes (P = 0.0006), high CD38 (P = 0.02) and high ZAP70 expression (P = 0.0017). Low CD21 expression was inversely correlated to the levels of phosphotyrosine induced in CLL cells following BCR ligation with αIgM (r2=–0.21). Importantly, lower CD21 expression was also predictive for reduced overall survival (P = 0.005; HR = 2.7). In conclusion, we showed that reduced expression of CD21 on CLL B-cells appears functionally relevant and was associated with poor clinical outcomes

Temple building on the Egyptian margins: the geopolitical issues behind Seti II and Ramesses IX’s activity at Amheida

Middle Eastern Studie

Glycan-independent role of calnexin in the intracellular retention of Charcot-Marie-Tooth 1A Gas3/PMP22 mutants

Missense point mutations in Gas3/PMP22 are responsible for the peripheral neuropathies Charcot-Marie-Tooth 1A and Dejerine Sottas syndrome. These mutations induce protein misfolding with the consequent accumulation of the proteins in the endoplasmic reticulum and the formation of aggresomes. During folding, Gas3/PMP22 associates with the lectin chaperone calnexin. Here, we show that calnexin interacts with the misfolded transmembrane domains of Gas3/PMP22, fused to green fluorescent protein, in a glycan-independent manner. In addition, photobleaching experiments in living cells revealed that Gas3/PMP22-green fluorescent protein mutants are mobile but diffuse at almost half the diffusion coefficient of wild type protein. Our results support emerging models for a glycan-independent chaperone role for calnexin and for the mechanism of retention of misfolded membrane proteins in the endoplasmic reticulum

A novel mutation of aprataxin associated with ataxia ocular apraxia type 1: Phenotypical and genotypical characterization

Ataxia oculomotor apraxia type 1 (AOA1) is the most common form of autosomal recessive ataxia in Japan, and the second in Portugal after Friedreich ataxia. AOA1 is typically characterized by early-onset cerebellar ataxia, oculomotor apraxia, hypoalbuminemia, hypercholesterolemia and late axonal sensori-motor neuropathy. AOA1 is associated with the aprataxin gene (APTX) encoding a protein involved in DNA repair. We characterized a novel homozygous missense mutation of APTX in a 34 year-old female patient born from consanguineous parents. The mutation, a Val230Gly caused by a c.689 T>G substitution, involved the histidine-triad (HIT) domain of the protein, affected a phylogenetically conserved amino acid and was absent in the control population. We described the clinical and neurophysiological features, the findings at structural and functional brain imaging, and the pathological picture of the sural nerve biopsy. The report emphasized the genetical and phenotypical heterogeneity of AOA1 by demonstrating atypical features such as absence of oculomotor apraxia and signs of pyramidal involvement. Expression studies by Western blotting on fibroblasts demonstrated that the homozygous Val230Gly mutation was associated with decreased levels of APTX indicating a loss-of-function mechanism

Deoxysphingolipids as candidate biomarkers for a novel SPTLC1 mutation associated with HSAN-I

[no abstract available

Parental mosaicism of a novel PMP22 mutation with a minimal neuropathic phenotype.

Genetic germinal and somatic mosaicisms of dominant Charcot-Marie-Tooth disease (CMT) mutations are rarely reported and/or recognized. We describe a novel heterozygous p.Trp39Cys missense mutation in the extracellular domain of the peripheral myelin protein 22 (PMP22) associated with an early-onset demyelinating CMT type 1 E (CMT1E) in two siblings born from asymptomatic non-consanguineous parents. The 29-year-old mother, harboring approximately 20% of the mutant PMP22 allele in blood, had minor signs of distal polyneuropathy (pes cavus, decreased ankle jerk reflexes and vibration sense in legs) and slight reduction of sural nerve action potentials (SNAPs). Authors suggest that mutations of CMT-related genes which originate in post-zygotic stages may be associated with mild phenotypes of peripheral neuropathy