Expanding the genetic and clinical spectrum of SORD-related peripheral neuropathy by reporting a novel variant c.210T>G and evidence of subclinical muscle involvement.

BACKGROUND AND AIMS: Biallelic variants in the sorbitol dehydrogenase (SORD) gene have been identified as the genetic cause of autosomal recessive (AR) peripheral neuropathy (PN) manifesting as Charcot-Marie-Tooth disease type 2 (CMT2) or distal hereditary motor neuropathy (dHMN). We aim to observe the genetic and clinical spectrum of a cohort of patients with SORD-related PN (SORD-PN). METHODS: A total of 107 patients with AR or sporadic CMT2/dHMN underwent molecular diagnosis by whole-exome sequencing and subsequent Sanger sequencing validation. Available phenotypic data for SORD-PN were collected and analyzed. RESULTS: Eleven (10.28%) of 107 patients were identified as SORD-PN, including four with CMT2 and seven with dHMN. The SORD variant c.210 T > G;p.His70Gln in F-d3 was firstly reported and subsequent analysis showed that it resulted in loss of SORD enzyme function. Evidence of subclinical muscle involvement was frequently detected in patients with SORD-PN, including mildly to moderately elevated serum creatine kinase (CK) levels in 10 patients, myogenic electrophysiological changes in one patient, and muscle edema in five patients undergoing lower extremity MRI. Fasting serum sorbitol level was 88-fold higher in SORD-PN patients (9.69 ± 1.07 mg/L) than in healthy heterozygous subjects (0.11 ± 0.01 mg/L) and 138-fold higher than in healthy controls (0.07 ± 0.02 mg/L). INTERPRETATION: The novel SORD variant c.210 T > G;p.His70Gln and evidence of subclinical muscle involvement were identified, which expanded the genetic and clinical spectrum of SORD-PN. Subclinical muscle involvement might be a common but easily overlooked clinical feature. The serum CK and fasting serum sorbitol levels were expected to be sensitive biomarkers confirmed by follow-up cohort study.

A medical odyssey of a 72-year-old man with Charcot-Marie-Tooth disease type 2 newly diagnosed with biallelic variants in SORD gene causing sorbitol dehydrogenase deficiency.

A 72-year-old man was referred to the Undiagnosed Diseases Network (UDN) because of gradual progressive weakness in both lower extremities for the past 45 years. He was initially diagnosed as having Charcot-Marie-Tooth disease type 2 (CMT2) without a defined molecular genetic cause. Exome sequencing (ES) failed to detect deleterious neuromuscular variants. Very recently, biallelic variants in sorbitol dehydrogenase (SORD) were discovered to be a novel cause of inherited neuropathies including CMT2 or distal hereditary motor neuropathy (dHMN) referred to as Sorbitol Dehydrogenase Deficiency with Peripheral Neuropathy (SORDD, OMIM 618912). The most common variant identified was c.757delG; p.A253Qfs*27. Through the Vanderbilt UDN clinical site, this patient was formally diagnosed with SORDD after the identification of homozygosity for the above SORD frameshift through UDN Genome Sequencing (GS). His medical odyssey was solved by GS and detection of extremely high levels of sorbitol. The diagnosis provided him the opportunity to receive potential treatment with an investigational drug in a clinical trial for SORDD. We suggest that similar studies be considered in other individuals thought to possibly have CMT2 or dHMN.

An inducible Komagataella phaffii system for protein expression using sorbitol dehydrogenase promoter.

OBJECTIVES: The aim of the present work was to develop a methanol-independent Komagataella phaffii (K. phaffii) strain using a non-methanol promoter. RESULTS: In this study, the food grade enzyme xylanase from Aspergillus niger ATCC 1015 was used as the reporter protein, a recombinant K. phaffii containing a cascade gene circus was designed and constructed using sorbitol as inducer. Sorbitol induced PSDH leading to MIT1 expression firstly, and heterologous protein xylanase expression finally. This system showed 1.7 fold of xylanase activity at the condition of single copy number of extra MIT1, and 2.1 fold of xylanase activity at condition of multi-copy extra MIT1 gene. CONCLUSIONS: This sorbitol-induced expression system of K. phaffii avoided toxic and explosive methanol. It was a novel cascade gene expression and a food safety system.

Sorbitol reduction via govorestat ameliorates synaptic dysfunction and neurodegeneration in sorbitol dehydrogenase deficiency.

Sorbitol dehydrogenase (SORD) deficiency has been identified as the most frequent autosomal recessive form of hereditary neuropathy. Loss of SORD causes high sorbitol levels in tissues due to the inability to convert sorbitol to fructose in the 2-step polyol pathway, leading to degenerative neuropathy. The underlying mechanisms of sorbitol-induced degeneration have not been fully elucidated, and no current FDA-approved therapeutic options are available to reduce sorbitol levels in the nervous system. Here, in a Drosophila model of SORD deficiency, we showed synaptic degeneration in the brain, neurotransmission defect, locomotor impairment, and structural abnormalities in the neuromuscular junctions. In addition, we found reduced ATP production in the brain and ROS accumulation in the CNS and muscle, indicating mitochondrial dysfunction. Applied Therapeutics has developed a CNS-penetrant next-generation aldose reductase inhibitor (ARI), AT-007 (govorestat), which inhibits the conversion of glucose to sorbitol. AT-007 significantly reduced sorbitol levels in patient-derived fibroblasts, induced pluripotent stem cell-derived (iPSC-derived) motor neurons, and Drosophila brains. AT-007 feeding in Sord-deficient Drosophila mitigated synaptic degeneration and significantly improved synaptic transduction, locomotor activity, and mitochondrial function. Moreover, AT-007 treatment significantly reduced ROS accumulation in Drosophila CNS, muscle, and patient-derived fibroblasts. These findings uncover the molecular and cellular pathophysiology of SORD neuropathy and provide a potential treatment strategy for patients with SORD deficiency.

Membrane-bound sorbitol dehydrogenase is responsible for the unique oxidation of D-galactitol to L-xylo-3-hexulose and D-tagatose in Gluconobacter oxydans.

BACKGROUND: Gluconobacter oxydans, is used in biotechnology because of its ability to oxidize a wide variety of carbohydrates, alcohols, and polyols in a stereo- and regio-selective manner by membrane-bound dehydrogenases located in periplasmic space. These reactions obey the well-known Bertrand-Hudson's rule. In our previous study (BBA-General Subjects, 2021, 1865:129740), we discovered that Gluconobacter species, including G. oxydans and G. cerinus strain can regio-selectively oxidize the C-3 and C-5 hydroxyl groups of D-galactitol to rare sugars D-tagatose and L-xylo-3-hexulose, which represents an exception to Bertrand Hudson's rule. The enzyme catalyzing this reaction is located in periplasmic space or membrane-bound and is PQQ (pyrroloquinoline quinine) and Ca2+-dependent; we were encouraged to determine which type of enzyme(s) catalyze this unique reaction. METHODS: Enzyme was identified by complementation of multi-deletion strain of Gluconobacter oxydans 621H with all putative membrane-bound dehydrogenase genes. RESULTS AND CONCLUSIONS: In this study, we identified this gene encoding the membrane-bound PQQ-dependent dehydrogenase that catalyzes the unique galactitol oxidation reaction in its 3'-OH and 5'-OH. Complement experiments in multi-deletion G. oxydans BP.9 strains established that the enzyme mSLDH (encoded by GOX0855-0854, sldB-sldA) is responsible for galactitol's unique oxidation reaction. Additionally, we demonstrated that the small subunit SldB of mSLDH was membrane-bound and served as an anchor protein by fusing it to a red fluorescent protein (mRubby), and heterologously expressed in E. coli and the yeast Yarrowia lipolytica. The SldB subunit was required to maintain the holo-enzymatic activity that catalyzes the conversion of D-galactitol to L-xylo-3-hexulose and D-tagatose. The large subunit SldA encoded by GOX0854 was also characterized, and it was discovered that its 24 amino acids signal peptide is required for the dehydrogenation activity of the mSLDH protein. GENERAL SIGNIFICANCE: In this study, the main membrane-bound polyol dehydrogenase mSLDH in G. oxydans 621H was proved to catalyze the unique galactitol oxidation, which represents an exception to the Bertrand Hudson's rule, and broadens its substrate ranges of mSLDH. Further deciphering the explicit enzymatic mechanism will prove this theory.

Skeletal muscle involvement in biallelic SORD mutations: case report and review of the literature.

Biallelic mutations in the sorbitol dehydrogenase (SORD) gene have been identified as a genetic cause of autosomal recessive axonal Charcot-Marie-Tooth disease 2 (CMT2) and distal hereditary motor neuropathy (dHMN). We herein review the main phenotypes associated with SORD mutations and report the case of a 16-year-old man who was referred to our outpatient clinic for a slowly worsening gait disorder with wasting and weakness of distal lower limbs musculature. Since creatine phosphokinase (CPK) values were persistently raised (1.5fold increased) and a Next-Generation Sequencing CMT-associated panel failed in identifying pathogenic variants, a muscle biopsy was performed with evidence of alterations suggestive of a protein surplus distal myopathy. Finally, Whole-Exome Sequencing (WES) identified two pathogenic SORD variants in the heterozygous state: c.458C > A (p.Ala153Asp) and c.757delG (p.Ala253Glnfs*27). This is an isolated report of compound heterozygosity for two SORD mutations associated with clinical and histological signs of skeletal muscle involvement, expanding the phenotypic expression of SORD mutations.

Association of SORD mutation with autosomal recessive asymmetric distal hereditary motor neuropathy.

BACKGROUND: The aim of this study was to identify the underlying genetic defect in a family segregating autosomal recessive asymmetric hereditary motor neuropathy (HMN). Asymmetric HMN has not been associated earlier with SORD mutations. METHODS: For this study, we have recruited a family and collected blood samples from affected and normal individuals of a family. Detailed clinical examination and electrophysiological studies were carried out. Whole exome sequencing was performed to detect the underlying genetic defect in this family. The potential variant was validated using the Sanger sequencing approach. RESULTS: Clinical and electrophysiological examination revealed asymmetric motor neuropathy with normal nerve conduction velocities and action potentials. Genetic analysis identified a homozygous mononucleotide deletion mutation (c.757delG) in a SORD gene in a patient. This mutation is predicted to cause premature truncation of a protein (p.A253Qfs*27). CONCLUSIONS: Interestingly, the patient with homozygous SORD mutation demonstrates normal motor and nerve conduction velocities and action potentials. The affected individual describes in this study has a unique presentation of asymmetric motor neuropathy predominantly affecting the right side more than the left as supported by the clinical examination. This is the first report of SORD mutation from Saudi Arabia and this study further expands the phenotypic spectrum of SORD mutation.

Long read sequencing overcomes challenges in the diagnosis of SORD neuropathy.

Biallelic mutations in sorbitol dehydrogenase (SORD) have been recently identified as a common cause of recessive axonal Charcot-Marie-Tooth neuropathy (CMT2). We aimed to assess a novel long-read sequencing approach to overcome current limitations in SORD neuropathy diagnostics due to the SORD2P pseudogene and the phasing of biallelic mutations in recessive disease. We conducted a screen of our Australian whole exome sequencing (WES) CMT cohort to identify individuals with homozygous or compound heterozygous SORD variants. Individuals detected with SORD mutations then underwent long-read sequencing, clinical assessment, and serum sorbitol analysis. An individual was detected with compound heterozygous truncating mutations in SORD exon 7, NM_003104.5:c.625C>T (p.Arg209Ter) and NM_003104.5:c.757del (p.Ala253GlnfsTer27). Subsequent Oxford Nanopore Tech (ONT) long-read sequencing was used to successfully differentiate SORD from the highly homologous non-functional SORD2P pseudogene and confirmed that the mutations were biallelic through haplotype-resolved analysis. The patient presented with axonal sensorimotor polyneuropathy (CMT2) and ulnar neuropathy without compression at the elbow. Burning neuropathic pain in the forearms and feet was also reported and was exacerbated by alcohol consumption and improved with alcohol cessation. UPLC-tandem mass spectrometry confirmed that the patient had elevated serum sorbitol levels (12.0 mg/L) consistent with levels previously observed in patients with biallelic SORD mutations. This represents a novel clinical presentation and expands the phenotype associated with biallelic SORD mutations causing CMT2. Our study is the first report of long-read sequencing for an individual with CMT and demonstrates the utility of this approach for clinical genomics.

Clinical and pathological study of SORD-related distal motor neuropathy caused by novel compound heterozygous mutations in a Chinese patient.

Sorbitol dehydrogenase (SORD) has been identified as the causative gene of autosomal recessive distal hereditary motor neuropathies (dHMN). Here, we describe a 25-year-old woman who presented with progressive weakness of both lower limbs for the previous 10 years. Electrophysiological results suggested only a reduction in the compound muscle action potential (CMAP) amplitude of both the tibial and left deep peroneal nerves and neurogenic changes in needle EMG. A heterozygous c.757delG variant with a splicing c.786 + 1 G>A variant in the SORD gene was identified. A sural nerve biopsy revealed slight axon separation from the myelin sheath and thin myelin sheaths in very few nerve fibres and thickening of the microvasculature basement membrane. Our study expands the pathological and mutation spectrum of the SORD-related neuropathy.

Juvenile amyotrophic lateral sclerosis associated with biallelic c.757delG mutation of sorbitol dehydrogenase gene.

Mutation in the sorbitol dehydrogenase gene (SORD) has been recently described to cause axonal Charcot-Marie-Tooth disease (CMT), intermediate CMT, and distal hereditary motor neuropathy (dHMN). We herein report the case of a 24-year-old patient diagnosed with juvenile amyotrophic lateral sclerosis (JALS) who carried the homozygous c.757delG mutation in SORD. No other pathogenic variant in frequent JALS-causative genes was found. Our findings expand the phenotype related to SORD mutation, a new and potentially treatable genetic disease.

Variation in the promoter of the sorbitol dehydrogenase gene MdSDH2 affects binding of the transcription factor MdABI3 and alters fructose content in apple fruit.

Fructose (Fru) content is a key determinant of fruit sweetness and quality. An F1 hybrid population of the apple cultivars 'Honeycrisp' × 'Qinguan' was used to investigate the quantitative trait locus (QTL) regions and genes controlling Fru content in fruit. A stable QTL on linkage group (LG) 01 in 'Honeycrisp' was detected on the single nucleotide polymorphism (SNP) genetic linkage maps. In this region, a sorbitol dehydrogenase (SDH) gene, MdSDH2, was detected and showed promoter variations and differential expression patterns between 'Honeycrisp' and 'Qinguan' fruits as well as their hybrids. A SNP variant (A/G) in the MdSDH2 promoter region (SDH2p-491) affected the binding ability of the transcription factor MdABI3, which can affect the expression of MdSDH2. Promoter sequences with an A nucleotide at SDH2p-491 had stronger binding affinity for MdABI3 than those with a G. Among 27 domesticated apple cultivars and wild relatives, this SNP (A/G) was associated with Fru content. Our results indicate that MdSDH2 can alter Fru content as the major regulatory gene and that ABA signaling might be involved in Fru content accumulation in apple fruit.

Biallelic variants in the SORD gene are one of the most common causes of hereditary neuropathy among Czech patients.

Recently, biallelic variants in the SORD gene were identified as causal for axonal hereditary neuropathy (HN). We ascertained the spectrum and frequency of SORD variants among a large cohort of Czech patients with unknown cause of HN. Exome sequencing data were analysed for SORD (58 patients). The prevalent c.757del variant was tested with fragment analysis (931 patients). Sanger sequencing in additional 70 patients was done. PCR primers were designed to amplify the SORD gene with the exclusion of the pseudogene SORD2P. Sequence differences between gene and pseudogene were identified and frequencies of SNPs were calculated. Eighteen patients from 16 unrelated families with biallelic variants in the SORD gene were found and the c.757del was present in all patients on at least one allele. Three novel, probably pathogenic, variants were detected, always in a heterozygous state in combination with the c.757del on the second allele. Patients presented with a slowly progressive axonal HN. Almost all patients had moderate pes cavus deformity. SORD neuropathy is frequent in Czech patients and the third most common cause of autosomal recessive HN. The c.757del is highly prevalent. Specific amplification of the SORD gene with the exclusion of the pseudogene is essential for a precise molecular diagnostics.

Identification of coding region SNPs from specific and sensitive mRNA biomarkers for the deconvolution of the semen donor in a body fluid mixture.

mRNA markers provide a very promising method for the identification of human body fluids or tissues in the context of forensic investigations. Previous studies have shown that different body fluids can be distinguished from each other according to their specific mRNA biomarkers. In this study, we evaluated eight semen-specific mRNA markers (KLK3, NKX3-1, CKB, KLK2, PRAC1, SEMG1, TGM4, and SORD) that encompass 12 coding single nucleotide polymorphisms (cSNPs) to identify the semen contributor in a mixed stain. Five highly specific and sensitive mRNA markers for blood, menstrual blood, saliva, vaginal secretions, and skin were also incorporated into the PCR system as body fluid-positive controls. Reverse transcription polymerase chain reaction (RT-PCR), multiplex PCR and SNaPshot mini-sequencing assays were established for the identification of semen-specific mRNA. The amplicon size ranged from 133 to 337 bp. The semen-specific system was examined against blood, menstrual blood, saliva, vaginal secretions, and skin swabs. The eight mRNA biomarkers were semen-specific and could be successfully typed in laboratory-generated mixtures composed of different body fluids supplemented with 1 ng of semen cDNA. This system possessed a high sensitivity that ranged from 1:10-1:100 for detecting trace amounts of semen in semen-containing body fluid mixtures. Additionally, our results demonstrated that the cSNPs polymorphisms included in the mRNA markers were concordant with genomic DNA (gDNA). Despite the presence of other body fluids, the system exhibited high sensitivity and specificity to the semen in the mixture. In future studies, we will add other cSNPs from the semen-specific genes using massively parallel sequencing to further improve our system.

Molecular cloning and biochemical characterization of a NAD-dependent sorbitol dehydrogenase from cold-adapted Pseudomonas mandelii.

Sugar alcohols (polyols) have important roles as nutrients, anti-freezing agents and scavengers of free radicals in cold-adapted bacteria, but the characteristics of polyol dehydrogenases in cold-adapted bacteria remain largely unknown. In this study, based on the observation that a cold-adapted bacterium Pseudomonas mandelii JR-1 predominantly utilized d-sorbitol as its carbon source, among the four polyols examined (d-galactitol, d-mannitol, d-sorbitol and d-xylitol), we cloned and characterized a sorbitol dehydrogenase (SDH, EC 1.1.1.14) belonging to the short-chain dehydrogenase/reductase family from this bacterium (the SDH hereafter referred to as PmSDH). PmSDH contained Asn111, Ser140, Tyr153 and Lys157 as catalytic active site residues and existed as an ∼67-kDa dimer in size-exclusion chromatography. PmSDH converted d-sorbitol to d-fructose using nicotinamide adenine dinucleotide (NAD+) as a cofactor and, vice versa, d-fructose to d-sorbitol using nicotinamide adenine dinucleotide reduced (NADH) as a cofactor. PmSDH maintained its conformational flexibility, secondary and tertiary structures, and thermal stability at 4-25°C. These results indicate that PmSDH, which has a flexible structure and a high catalytic activity at colder temperatures, is well suited to sorbitol utilization in the cold-adapted bacterium P. mandelii JR-1.

Improvement of pyrroloquinoline quinone-dependent d-sorbitol dehydrogenase activity from Gluconobacter oxydans via expression of Vitreoscilla hemoglobin and regulation of dissolved oxygen tension for the biosynthesis of 6-(N-hydroxyethyl)-amino-6-deoxy-α-l-sorbofuranose.

The miglitol intermediate, 6-(N-hydroxyethyl)-amino-6-deoxy-α-l-sorbofuranose (6NSL), is catalyzed from N-2-hydroxyethyl glucamine (NHEG) by resting cells of Gluconobacter oxydans. One of the key factors limiting 6NSL production was the availability of oxygen during both cell cultivation and biotransformation of NHEG to 6NSL. Based on G. oxydans/pBBR1-sldAB-pqqABCDE-tldD (G. oxydans/AB-PQQ), the Vitreoscilla hemoglobin (VHb) was heterologously expressed in G. oxydans to enhance oxygen transfer efficiency and improve 6NSL production. The recombinant G. oxydans/AB-PQQ-VHb displayed higher biomass and NHEG oxidation activity than the control stain. The transcription levels of respiratory chain-related enzyme genes in G. oxydans/AB-PQQ-VHb exhibited up-regulation, indicating that the presence of VHb promoted the respiration. The dissolved oxygen (DO) concentration for cell cultivation was optimized in a 5-L stirred bioreactor. At a DO concentration of 20%, the maximum volumetric oxidation activity of NHEG of G. oxydans/AB-PQQ-VHb in the stirred bioreactor reached 168.3 ± 3.2 U/L. Furthermore, the biotransformation of NHEG to 6NSL using G. oxydans/AB-PQQ-VHb was carried out under different oxygen tensions to investigate the effect of oxygen on 6NSL production. Finally, up to 87.5 ± 5.9 g/L 6NSL was accumulated in the reaction mixture within 16 h when the DO was controlled at 30%.

Effects of abiotic stresses on sorbitol biosynthesis and metabolism in tomato (Solanum lycopersicum).

Polyols such as sorbitol and ribitol are a class of compatible solutes in plants that may play roles in tolerance to abiotic stresses. This study investigated the effects of water stress on sorbitol biosynthesis and metabolism and sorbitol and ribitol accumulation in tomato (Solanum lycopersicum L.). Water stress induced by withholding water and by using polyethylene glycol as a root incubation solution to mimic water stress, and NaCl stress were applied to wild-type (WT) and three genetically-modified lines of tomato (cv. Ailsa Craig), a control vector line TR22, and 2 sorbitol dehydrogenase (sdh) antisense lines TR45 and TR49. Sorbitol and ribitol content, as well as the enzymatic activities, protein accumulation, and gene expression patterns of the key sorbitol cycle enzymes aldose-6-phosphate reductase (A6PR), aldose reductase (AR), and sorbitol dehydrogenase (SDH), were measured in mature leaves. In response to the stresses, both sorbitol and ribitol accumulated in leaf tissue, most significantly in the sdh antisense lines. A6PR, characterised for the first time in this work, and AR both exhibited increased enzymatic activity correlated with sorbitol accumulation during the stress treatments, with SDH also increasing in WT and TR22 to metabolise sorbitol, reducing the content to control levels within 3 days after re-watering. In the sdh antisense lines, the lack of significant SDH activity resulted in the increased sorbitol and ribitol content above WT levels. The results highlighted a role for both A6PR and AR in biosynthesis of sorbitol in tomato where the high activity of both enzymes was associated with sorbitol accumulation. Although both A6PR and AR are aldo-keto reductases and use NADPH as a co-factor, the AR-specific inhibitor sorbinil inhibited AR only indicating that they are different enzymes. The determination that sorbitol, and perhaps ribitol as well, plays a role in abiotic responses in tomato provides a cornerstone for future studies examining how they impact tomato tolerance to abiotic stresses, and if their alteration could improve stress tolerance.

Evaluation of SORD mutations as a novel cause of Charcot-Marie-Tooth disease.

Biallelic mutations in the sorbitol dehydrogenase (SORD) encoding gene were recently identified as a common genetic cause in autosomal-recessive CMT patients. Here, we investigated the clinical, genetic, and electrophysiological characteristics of three CMT patients with biallelic SORD mutations from a Chinese cohort. Two patients harbored c.757delG (p.A253Qfs*27) homozygous mutations, and one patient carried both c.757delG (p.A253Qfs*27) and c.625C>T (p.R209X) compound heterozygous mutations. Interestingly, the two patients homozygous for the c.757delG mutation exhibited positive responses for pinprick test. In conclusion, we confirmed SORD mutations as causative for CMT and further expanded the mutational and phenotypic spectrum of SORD-related CMT.

Kinetic characterization and structure analysis of an altered polyol dehydrogenase with d-lactate dehydrogenase activity.

During adaptive metabolic evolution a native glycerol dehydrogenase (GDH) acquired a d-lactate dehydrogenase (LDH) activity. Two active-site amino acid changes were detected in the altered protein. Biochemical studies along with comparative structure analysis using an X-ray crystallographic structure model of the protein with the two different amino acids allowed prediction of pyruvate binding into the active site. We propose that the F245S alteration increased the capacity of the glycerol binding site and facilitated hydrogen bonding between the S245 γ-O and the C1 carboxylate of pyruvate. To our knowledge, this is the first GDH to gain LDH activity due to an active site amino acid change, a desired result of in vivo enzyme evolution.

Recent Advances in Drosophila Models of Charcot-Marie-Tooth Disease.

Charcot-Marie-Tooth disease (CMT) is one of the most common inherited peripheral neuropathies. CMT patients typically show slowly progressive muscle weakness and sensory loss in a distal dominant pattern in childhood. The diagnosis of CMT is based on clinical symptoms, electrophysiological examinations, and genetic testing. Advances in genetic testing technology have revealed the genetic heterogeneity of CMT; more than 100 genes containing the disease causative mutations have been identified. Because a single genetic alteration in CMT leads to progressive neurodegeneration, studies of CMT patients and their respective models revealed the genotype-phenotype relationships of targeted genes. Conventionally, rodents and cell lines have often been used to study the pathogenesis of CMT. Recently, Drosophila has also attracted attention as a CMT model. In this review, we outline the clinical characteristics of CMT, describe the advantages and disadvantages of using Drosophila in CMT studies, and introduce recent advances in CMT research that successfully applied the use of Drosophila, in areas such as molecules associated with mitochondria, endosomes/lysosomes, transfer RNA, axonal transport, and glucose metabolism.

Combinational expression of D-sorbitol dehydrogenase and pyrroloquinoline quinone increases 6-(N-hydroxyethyl)-amino-6-deoxy-α-L-sorbofuranose production by Gluconobacter oxydans through cofactor manipulation.

6-(N-hydroxyethyl)-amino-6-deoxy-l-sorbofuranose (6NSL), a key precursor in the synthesis of miglitol, is produced from N-2-hydroxyethyl-glucamine (NHEG) by the regioselective oxidation of Gluconobacter oxydans. The limitation of PQQ biosynthesis became a bottleneck for improvement of PQQ-dependent D-sorbitol dehydrogenase (mSLDH) activity. Five expression plasmids were constructed for the co-expression of the pqqABCDE gene cluster and the tldD gene on the basis of pBBR1-gHp0169-sldAB in G. oxydans to increase the biosynthesis of PQQ. The G. oxydans/pGA004, in which pqqABCDE and tldD were expressed as a cluster under the control of gHp0169 promoter, showed the optimal performance. The intracellular PQQ concentration and specific activity of mSLDH in cells increased by 79.3 % and 53.7 %, respectively, compared to that in G. oxydans/pBBR-sldAB. Then, the repeated batch biotransformation of NHEG to 6NSL by G. oxydans/pGA004 was carried out. Up to 75.0 ±â€¯3.0 g/L of 6NSL production with 94.5 ±â€¯3.6 % of average conversion rate of NHEG to 6NSL was achieved after four cycles of run. These results indicated that G. oxydans/pGA004 with high productivity had great potential for 6NSL production in industrial bioprocess.