A novel mutation in the FGD4 gene causing Charcot-Marie-Tooth disease

Lamivudine modulates the expression of neurological impairment-related genes and LINE-1 retrotransposons in brain tissues of a Down syndrome mouse model

Elevated activity of retrotransposons is increasingly recognized to be implicated in a wide range of neurodegenerative and neurodevelopmental diseases, including Down syndrome (DS), which is the most common chromosomal condition causing intellectual disability globally. Previous research by our group has revealed that treatment with lamivudine, a reverse transcriptase inhibitor, improved neurobehavioral phenotypes and completely rescued hippocampal-dependent recognition memory in a DS mouse model, Ts65Dn. We hypothesized that retrotransposition rates would increase in the Ts65Dn mouse model, and lamivudine could block retrotransposons. We analyzed the differentially expressed long interspersed element-1 (LINE-1 or L1) mapping on MMU16 and 17, and showed for the first time that retrotransposition could be associated with Ts65Dn's pathology, as misregulation of L1 was found in brain tissues associated with trisomy. In the cerebral cortex, 6 out of 26 upregulated L1s in trisomic treated mice were located in the telomeric region of MMU16 near Ttc3, Kcnj6, and Dscam genes. In the hippocampus, one upregulated L1 element in trisomic treated mice was located near the Fgd4 gene on MMU16. Moreover, two downregulated L1s rescued after treatment with lamivudine were located in the intronic region of Nrxn1 (MMU17) and Snhg14 (MMU7), implicated in a variety of neurodegenerative disorders. To gain further insight into the mechanism of this improvement, we here analyzed the gene expression profile in the hippocampus and cerebral cortex of trisomic mice treated and no-treated with lamivudine compared to their wild-type littermates. We found that treatment with lamivudine rescued the expression of 24% of trisomic genes in the cortex (located on mouse chromosome (MMU) 16 and 17) and 15% in the hippocampus (located in the human chromosome 21 orthologous regions), with important DS candidate genes such as App and Ets2, rescued in both regions.

A Novel Mutation in Frabin (FGD4) Causing a Mild Phenotype of CMT4H in an Indian Patient

Charcot-Marie-Tooth disease 4H(CMT4H) is an autosomal recessive demyelinating form of CMT caused by FGD4/FRABIN mutations. CMT4H is characterized by early onset and slowly progressing motor and sensory deficits in the distal extremities, along with foot deformities. We describe a patient with CMT4H who presented with rapidly progressing flaccid quadriparesis during the postpartum period, which improved significantly with steroid therapy. Magnetic resonance imaging and ultrasonography demonstrated considerable nerve thickening with increased cross-sectional area in the peripheral nerves. A nerve biopsy revealed significant demyelination and myelin outfolding. This is the first report of an Indian patient with a novel homozygous nonsense c.1672C>T (p.Arg558Ter) mutation in the FGD4 gene, expanding the mutational and phenotypic spectrum of this disease.

Sibling Cases of Charcot-Marie-Tooth Disease Type 4H with a Homozygous FGD4 Mutation and Cauda Equina Thickening

Charcot-Marie-Tooth disease type 4H (CMT4H) is an autosomal recessive inherited demyelinating neuropathy caused by an FYVE, RhoGEF, and a PH domain-containing protein 4 (FGD4) gene mutation. CMT4H is characterized by an early onset, slow progression, scoliosis, distal muscle atrophy, and foot deformities. We herein present sibling cases of CMT4H with a homozygous mutation in the FGD4 gene. Both patients exhibited cauda equina thickening on magnetic resonance imaging, which had not been reported among the previous CMT4H cases. This is the first report of CMT4H with a homozygous FGD4 c.1730G>A (p.Arg577Gln) mutation showing mild progression and cauda equina thickening.

MiR-23a induced the activation of CDC42/PAK1 pathway and cell cycle arrest in human cov434 cells by targeting FGD4

Background

MiRNAs play important roles in the development of ovarian cancer, activation of primitive follicles, follicular development, oocyte maturation and ovulation. In the present study, we investigated the specific role of miR-23a in cov434 cells.

Results

Downregulation of miR-23a was observed in serum of PCOS patients compared with the healthy control, suggesting the inhibitory effect of miR-23a in PCOS. MiR-23a was positively correlated with Body Mass Index (BMI) and negatively correlated with Luteinizing hormone (LH), Testostrone (T), Glucose (Glu) and Insulin (INS) of PCOS patients. MiR-23a mimic inhibited the proliferation and promoted apoptosis of human cov434 cells. In addition, flow cytometry assay confirmed that miR-23a blocked cell cycle on G0/G1 phase. MiR-23a inhibitor showed opposite results. Furthermore, double luciferase reporter assay proved that miR-23a could bind to the 3’UTR of FGD4 directly through sites predicted on Target Scan. FGD4 level was significantly suppressed by miR-23a mimic, but was significantly enhanced by miR-23a inhibitor. We further proved that miR-23a increased the expression of activated CDC42 (GTP bround) and p-PAK-1, suggesting that miR-23a induced cell cycle arrest through CDC42/PAK1 pathway.

Conclusions

In conclusion, our study reveals that miR-23a participates in the regulation of proliferation and apoptosis of cov434 cells through target FGD4, and may play a role in the pathophysiology of PCOS.

Structural and functional divergence of GDAP1 from the glutathione S-transferase superfamily

Mutations in ganglioside-induced differentiation-associated protein 1 (GDAP1) alter mitochondrial morphology and result in several subtypes of the inherited peripheral neuropathy Charcot-Marie-Tooth disease; however, the mechanism by which GDAP1 functions has remained elusive. GDAP1 contains primary sequence homology to the GST superfamily; however, the question of whether GDAP1 is an active GST has not been clearly resolved. Here, we present biochemical evidence, suggesting that GDAP1 has lost the ability to bind glutathione without a loss of substrate binding activity. We have revealed that the α-loop, located within the H-site motif is the primary determinant for substrate binding. Using structural data of GDAP1, we have found that critical residues and configurations in the G-site which canonically interact with glutathione are altered in GDAP1, rendering it incapable of binding glutathione. Last, we have found that the overexpression of GDAP1 in HeLa cells results in a mitochondrial phenotype which is distinct from oxidative stress-induced mitochondrial fragmentation. This phenotype is dependent on the presence of the transmembrane domain, as well as a unique hydrophobic domain that is not found in canonical GSTs. Together, we data point toward a non-enzymatic role for GDAP1, such as a sensor or receptor.

A very mild phenotype of Charcot-Marie-Tooth disease type 4H caused by two novel mutations in FGD4

BACKGROUND

Mutations in the FGD4 gene cause an autosomal recessive demyelinating peripheral neuropathy referred to as CMT4H, characterized by its onset in infancy or early-childhood and its slow progression.

METHODS

The clinical and genetic status of two patients with CMT4H was studied, performing genetic testing with a panel of genes and analysing FGD4 mRNA expression by quantitative PCR.

RESULTS

Two novel FGD4 variants (c.514delG and c.2211dupA) were identified in two mildly affected Spanish siblings with CMT4H, and with disease onset in late adolescence/adulthood (one of them remaining asymptomatic at 20). On examination, foot deformity was observed without weakness or sensory involvement, and in the muscles of the lower extremities magnetic resonance imaging showed no fat replacement. Further analysis of FGD4 expression in peripheral blood suggested that neither mutation affected splicing, nor did they affect the dosage of FGD4 mRNA (compared to a healthy control). It was predicted that each allele would produce a truncated protein, p.Ala172Glnfs*28 (c.514delG) and p.Ala738Serfs*5 (c.2211dupA), the latter containing all the functional domains of the native protein.

CONCLUSIONS

The conservation of functional domains in the proteins produced from the FGD4 gene of two patients with CMT4H, could explain both the milder phenotype and the later disease onset in these patients. These results expand the clinical and mutational spectrum of FGD4-related peripheral neuropathies.