Niemann‐Pick C disease (NPC) is an autosomal recessive neurodegenerative disorder caused by the abnormal function of NPC1 or NPC2 proteins, leading to an accumulation of unesterified cholesterol and glycosphingolipids (GSLs) in the lysosomes. The mechanisms underlying the pathophysiology in NPC disease are not clear. Oxidative damage is implicated in the pathophysiology of different neurological disorders and the effect of GSL accumulation on the intracellular redox state has been documented. Therefore, we determined whether the intracellular redox state might contribute to the NPC disease pathophysiology. Because the treatment of NPC mice with allopregnanolone (ALLO) increases their lifespan and delays the onset of neurological impairment, we analysed the effect of ALLO on the oxidative damage in human NPC fibroblasts. Concentrations of reactive oxygen species (ROS) and lipid peroxidation were higher in fibroblasts from NPC patients than in fibroblasts from normal subjects. Fibroblasts from NPC patients were more susceptible to cell death through apoptosis after an acute oxidative insult. This process is mediated by activation of the NF‐κB signalling pathway. Knockdown of NPC1 mRNA both in normal fibroblasts and in human SH‐SY5Y neuroblastoma cells caused increased ROS concentrations. ALLO treatment of fibroblasts from NPC patients or NPC1 knockdown cells reduced the levels of ROS and lipid peroxidation and prevented peroxide‐induced apoptosis and NF‐kB activation. Thus, these findings suggest that oxidative stress might contribute to the NPC disease and ALLO might be beneficial in the treatment of the disease, at least in part, due to its ability to restore the intracellular redox state.

Niemann-Pick Types A and B (NPA/B) diseases are autosomal recessive lysosomal storage disorders caused by the deficient activity of acid sphingomyelinase (ASM) because of the mutations in the SMPD1 gene. Here, we provide a comprehensive updated review of already reported and newly identified SMPD1 variants. Among them, 185 have been found in NPA/B patients. Disease-causing variants are equally distributed along the SMPD1 gene; most of them are missense (65.4%) or frameshift (19%) mutations. The most frequently reported mutation worldwide is the p.R610del, clearly associated with an attenuated NP disease type B phenotype. The available information about the impact of 52 SMPD1 variants on ASM mRNA and/or enzymatic activity has been collected and whenever possible, phenotype/genotype correlations were established. In addition, we created a locus-specific database easily accessible at http://www.inpdr.org/genes that catalogs the 417 SMPD1 variants reported to date and provides data on their in silico predicted effects on ASM protein function or mRNA splicing. The information reviewed in this article, providing new insights into the genotype/phenotype correlation, is extremely valuable to facilitate diagnosis and genetic counseling of families affected by NPA/B.

Glycogen storage disease type II is a lysosomal storage disorder due to mutations of the GAA gene, which causes lysosomal alpha-glucosidase deficiency. Clinically, glycogen storage disease type II has been classified in infantile and late-onset forms. Most late-onset patients share the leaky splicing mutation c.-32-13T>G. To date, the mechanism by which the c.-32-13T>G mutation affects the GAA mRNA splicing is not fully known. In this study, we demonstrate that the c.-32-13T>G mutation abrogates the binding of the splicing factor U2AF65 to the polypyrimidine tract of exon 2 and that several splicing factors affect exon 2 inclusion, although the only factor capable of acting in the c.-32-13 T>G context is the SR protein family member, SRSF4 (SRp75). Most importantly, a preliminary screening using small molecules described to be able to affect splicing profiles, showed that resveratrol treatment resulted in a significant increase of normal spliced GAA mRNA, GAA protein content and activity in cells transfected with a mutant minigene and in fibroblasts from patients carrying the c-32-13T>G mutation. In conclusion, this work provides an in-depth functional characterization of the c.-32-13T>G mutation and, most importantly, an in vitro proof of principle for the use of small molecules to rescue normal splicing of c.-32-13T>G mutant alleles.

Gaucher disease is the most frequent lysosomal storage disorder due to the deficiency of the acid β-glucosidase, encoded by the GBA gene. In this study, we report the structural and functional characterization of 11 novel GBA alleles. Seven single missense alleles, P159S, N188I, E235K, P245T, W312S, S366R and W381C, and two alleles carrying in cis mutations, (N188S; G265R) and (E326K; D380N), were studied for enzyme activity in transiently transfected cells. All mutants were inactive except the P159S, which retained 15% of wild-type activity. To further characterize the alleles carrying two in cis mutations, we expressed constructs bearing singly each mutation. The presence of G265R or D380N mutations completely abolished enzyme activity, while N188S and E326K mutants retained 25 and 54% of wild-type activity, respectively. Two mutations, affecting the acceptor splice site of introns 5 (c.589-1G>A) and 9 (c.1389-1G>A), led to the synthesis of aberrant mRNA. Unpredictably, family studies showed that two alleles resulted from germline or ‘de novo’ mutations. These results strengthen the importance of performing a complete and accurate molecular analysis of the GBA gene in order to avoid misleading conclusions and provide a comprehensive functional analysis of new GBA mutations.