Anja Schirmacher

Mutations in SEPT9 cause hereditary neuralgic amyotrophy

Hereditary neuralgic amyotrophy (HNA) is an autosomal dominant recurrent neuropathy affecting the brachial plexus. HNA is triggered by environmental factors such as infection or parturition. We report three mutations in the gene septin 9 (SEPT9) in six families with HNA linked to chromosome 17q25. HNA is the first monogenetic disease caused by mutations in a gene of the septin family. Septins are implicated in formation of the cytoskeleton, cell division and tumorigenesis.

Association of the functional V158M catechol-O-methyl-transferase polymorphism with panic disorder in women.

Panic disorder is an anxiety disorder with an estimated heritability of up to 48%. Pharmacological and genetic studies suggest that genes coding for proteins involved in the catecholaminergic system might be relevant for the pathogenesis of the disease. In the present study, we genotyped a single nucleotide polymorphism (472G/A=V158M) in the coding region of the catechol-O-methyl-transferase (COMT) gene in 115 patients with panic disorder and age- and sex-matched controls. Association analysis revealed a significant excess of the more active COMT allele (472G=V158) in patients with panic disorder (p=0.04), particularly in female patients (p=0.01), but not in male patients (p=1.0). The assessment of a possible interaction of the COMT polymorphism with a previously reported functional 30-bp VNTR in the monoamine oxidase A promoter (MAOALPR) in female patients did not yield significant results. Our data support a role of the 472G/A (V158M) COMT polymorphism or a nearby locus in the pathogenesis of panic disorder in women.

Interaction of BDNF and COMT Polymorphisms on Paired-Associative Stimulation-Induced Cortical Plasticity

The common single-nucleotide polymorphism (SNP) brain-derived neurotrophic factor (BDNF) valine-to-methionine substitution at codon 66 (Val66Met) has been associated with differences in memory functions and cortical plasticity following brain stimulation. Other studies could not confirm these results, though, and potential interactions of BDNF carrier status with other learning-relevant SNPs are largely unknown. The present study aimed to evaluate the effects of BDNF Val66Met genotype on paired associative stimulation (PAS)-induced motor cortex plasticity, while additionally taking catechol-O-methyltransferase (COMT) Val158Met and kidney and brain (KIBRA) rs17070145 carrier status into account. Therefore, a cohort of 2 × 16 age- and education-matched healthy young females underwent transcranial magnetic stimulation using an excitatory PAS25 protocol to induce cortical plasticity. Cognitive performance was assessed using implicit grammar- and motor-learning tasks and a detailed neuropsychological test battery. While BDNF carrier status alone did not significantly influence PAS-induced cortical plasticity, we found a significant BDNF × COMT interaction, showing higher plasticity immediately following the PAS25 protocol for the BDNF Val/Val vs Met genotype in COMT Met homozygotes only (ANOVA, p = 0.027). A similar advantage for this group was noted for implicit grammar learning (ANOVA, p = 0.021). Accounting for KIBRA rs17070145 did not explain significant variance. Our findings for the first time demonstrate an interaction of BDNF by COMT on human cortical plasticity. Moreover, they show that genotype-related differences in neurophysiology translate into behavioral differences. These findings might contribute to a better understanding of the mechanisms of interindividual differences in cognition.

Giant axonal neuropathy (GAN): Case report and two novel mutations in the gigaxonin gene

Abstract—Giant axonal neuropathy (GAN) is an autosomal recessive neurologic disorder clinically characterized by a severe polyneuropathy, CNS abnormalities, and characteristic tightly curled hair. Recently, mutations in the gigaxonin gene have been identified as the underlying genetic defect. The authors report two novel mutations confirming that GAN is caused by mutations in the gigaxonin gene and raise the question whether some mutations may cause a mild subclinical neuropathy.

Cholecystokinin- and cholecystokinin-B-receptor gene polymorphisms in panic disorder

Panic disorder like other neuropsychiatric disorders is believed to be caused by multiple psychosocial and biological factors. Several lines of evidence point to a role for the peptide neurotransmitter cholecystokinin in the pathogenesis of panic disorder. We therefore determined the allele and genotype frequencies of a single nucleotide polymorphism in the CCK gene (-36C>T) and one CT repeat polymorphism in the CCK-B-receptor gene in a German panic disorder sample (n = 115 for CCK gene polymorphism, n = 111 for CCK-B-receptor polymorphism) and compared them with gender and age matched controls. The length of the polymorphic CT repeat alleles varies between 146 bp and 180 bp. We first analysed the results by a permutation test which provided evidence for heterogeneity between patients and controls (p=0.002). We then analysed the data as a di-allelic polymorphism with a short (146-162bp) and a long (164-180bp) allele and as a tetra-allelic polymorphism with 4 alleles (146-154bp, 156-162bp, 164-170bp, 172-180bp). In the di-allelic analysis as well as in the tetra-allelic analysis there was an excess of the longer allele (p = 0.001) or the two longer alleles (p = 0.041) respectively in patients with panic disorder. No difference between groups was observed for the -36C > T polymorphism. Our findings are consistent with the notion that genetic variation in the CCK neurotransmitter system contributes to the pathogenesis of panic disorder.

Charcot-Marie-Tooth disease: Frequency of genetic subtypes in a German neuromuscular center population

Charcot-Marie-Tooth (CMT) neuropathies belong to the most common neurogenetic disorders. To date, mutations in more than 40 genes are known to be able to cause CMT. This genetic heterogeneity is a challenge for genetic diagnostics. Data on frequencies of mutations in CMT genes from large patient cohorts are needed to develop strategies for efficient genetic testing. In this study we have analysed patient histories, electrophysiological and genetic testing data in our cohort of 776 patients. In electrophysiologically demyelinating CMT, PMP22 duplication was the most common genetic cause, followed by mutations in GJB1 and MPZ. In axonal CMT, GJB1 was the most commonly affected gene, followed by MFN2 and MPZ. In CMT1, the clearance rate was 66%, in CMT2 it was 35%. Overall, the genetic clearance rate in our patient cohort was 58%. We found a higher rate of genetic diagnosis in patients seen in our neuromuscular center compared to out-of-clinic patients whose DNA was tested in our laboratory. This study provides further data on frequencies of CMT genes and subtypes and points to the importance of a thorough clinical and electrophysiological work-up for the direction of genetic testing.

Human nuclear transcription factor gene CREM: Genomic organization, mutation screening, and association analysis in panic disorder

Panic disorder is an anxiety disorder with an estimated heritability of 48%. Variation in the gene of the nuclear transcription factor “cAMP‐responsive element modulator” (CREM) might contribute to its pathogenesis. CREM knock‐out mice exhibit significantly less anxiety behavior than wild‐type mice and the alternative CREM gene product “inducible cAMP early repressor” (ICER) plays a pivotal role in the hypothalamo‐pituitary‐adrenal (HPA) axis, which is disturbed in panic disorder. We characterized the genomic organization of the human CREM gene and performed a systematic mutation screening by means of single stranded conformational analysis (SSCA) in a sample of 40 German patients with panic disorder (DSM‐III‐R). Four novel single nucleotide polymorphisms in CREM promoters P 1 and P 4, one trinucleotide (ATT)‐repeat polymorphism in CREM promoter P 2—generating the ICER isoform—and a rare amino acid substitution in CREM exon glut 2 were identified. Association analysis in an extended sample of German patients (n = 88) revealed a significant excess of the shorter CREM P 2 promoter eight‐repeat trinucleotide allele and of genotypes containing the eight‐repeat trinucleotide allele in panic disorder (P = 0.02), in particular in panic disorder without agoraphobia (P = 0.001). A replication study in independent Italian (n = 76) and Spanish (n = 62) samples, however, failed to confirm this observation. This suggests that the CREM P 2 promoter trinucleotide polymorphism is not a major susceptibility factor in the pathogenesis of panic disorder. Functional analysis of the observed CREM P 2 promoter polymorphism as well as studies in independent panic disorder samples are necessary.

Enhanced Rapid-Onset Cortical Plasticity in CADASIL as a Possible Mechanism of Preserved Cognition

Ischemic small vessel disease (SVD) may lead to cognitive impairment, but cognitive deficits with a given burden of SVD vary significantly. The underlying mechanisms of impaired or preserved cognition are unknown. Here, we investigated the impact of ischemic SVD on rapid-onset cortical plasticity, as induced with a paired-associative stimulation protocol. To exclude concomitant effects of aging, we examined 12 middle-aged patients (48.3 ± 8.3 years) with cerebral autosomal dominant arteriopathy with subcortical infarctions and leucoencephalopathy (CADASIL) who suffered from severe ischemic SVD and a group of 12 age-matched controls (49.9 ± 8.3 years). Cognitive status, motor performance and learning, and motor cortex excitability in response to cathodal transcranial direct current stimulation (ctDCS) were assessed. White matter integrity was analyzed by conventional magnetic resonance imaging and diffusion tensor imaging. We found that cognitive and motor functions were largely preserved in CADASIL patients, while rapid-onset cortical plasticity was significantly higher in the CADASIL group compared with controls (repeated measures analysis of variance [group × time] interaction: P = 0.03). This finding was even more pronounced in patients with higher white matter lesion load. ctDCS revealed no evidence of cortical dysplasticity. We conclude that increased rapid-onset cortical plasticity may contribute to largely preserved cognitive and motor function despite extensive ischemic SVD.

Kinetics of 3-[123I]iodo-l-α-methyltyrosine transport in rat C6 glioma cells

Abstract. 3-[123I]Iodo-l-α-methyltyrosine (123I-IMT) is used for the diagnosis and monitoring of brain tumours by means of single-photon emission tomography (SPET). To date, little has been known about the system for the transport of 123I-IMT into brain tumour cells. It is assumed that 123I-IMT is transported by a specific carrier for large, neutral amino acids (L-system). In this study, rat C6 glioma cells were used to characterize the uptake system of 123I-IMT and to investigate its precise kinetics. The time course of 123I-IMT uptake into the cells was examined for a range of 1–60 min. 123I-IMT uptake rates with varying concentrations of 123I-IMT (2.5–50 µM) in the medium were quantified to assess the kinetic parameters of 123I-IMT transport. Furthermore, competition of 123I-IMT with other amino acids was investigated to identify the distinct transport systems involved in 123I-IMT uptake. 123I-IMT uptake into C6 glioma cells was linear for approximately 10 min and reached a steady-state level within 30 min. The analysis of the rate of uptake of 123I-IMT at different concentrations was concordant with the predominance of a single uptake system. The apparent Michaelis constant (Km) of 123I-IMT was 26.2±1.9 µM, and the maximum transport velocity (Vmax) was 35.4±1.7 nmol/mg protein per 10 min. 77%±10% of 123I-IMT transport was sodium independent and 23%±3% was sodium dependent. Competitive inhibition of 123I-IMT uptake by 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid, α-(methylamino)isobutyric acid and naturally occurring amino acids revealed a major 123I-IMT transport via the sodium-independent system L (72%) and a minor uptake via the sodium-dependent system B0,+ (17%). Our results show that 123I-IMT transport into C6 glioma cells is principally mediated by the L-system and to a minor extent by the B0,+-system. The kinetic parameters of 123I-IMT uptake are in the range of those of naturally occurring amino acids.

Genotype-phenotype analysis in patients with giant axonal neuropathy (GAN)

Giant axonal neuropathy (GAN, MIM: 256850) is a devastating autosomal recessive disorder characterized by an early onset severe peripheral neuropathy, varying central nervous system involvement and strikingly frizzly hair. Giant axonal neuropathy is usually caused by mutations in the gigaxonin gene (GAN) but genetic heterogeneity has been demonstrated for a milder variant of this disease. Here, we report ten patients referred to us for molecular genetic diagnosis. All patients had typical clinical signs suggestive of giant axonal neuropathy. In seven affected individuals, we found disease causing mutations in the gigaxonin gene affecting both alleles: two splice-site and four missense mutations, not reported previously. Gigaxonin binds N-terminally to ubiquitin activating enzyme E1 and C-terminally to various microtubule associated proteins causing their ubiquitin mediated degradation. It was shown for a number of gigaxonin mutations that they impede this process leading to accumulation of microtubule associated proteins and there by impairing cellular functions.