Whole-brain T2 mapping demonstrates occult abnormalities in focal epilepsy.

OBJECTIVES: To examine the cerebral structure of 14 patients with partial seizures and acquired lesions, 20 patients with malformations of cortical development (MCDs), and 45 patients with partial seizures and normal conventional MRI using whole-brain T2 mapping and statistical parametric mapping (SPM). METHODS: T2 maps were calculated, and individual patients were compared with a group of 30 control subjects using SPM. RESULTS: T2 mapping and objective voxel-by-voxel statistical comparison identified regions of increased T2 signal in all 14 patients with acquired nonprogressive cerebral lesions and partial seizures. In all of these, the areas of increased T2 signal concurred with abnormalities identified on visual inspection of conventional MRI. In 18 of 20 patients with MCDs, SPM detected regions of increased T2 signal, all of which corresponded to abnormalities identified on visual inspection of conventional MRI. In addition, in both groups, there were areas that were normal on conventional imaging, which demonstrated abnormal T2 signal. Voxel-by-voxel statistical analysis identified increased T2 signal in 23 of the 45 patients with cryptogenic focal epilepsy. In 20 of these, the areas of increased T2 signal concurred with epileptiform EEG abnormality and clinical seizure semiology. Group analysis of MRI-negative patients with electroclinical seizure onset localizing to the left and right temporal and left and right frontal regions revealed increased T2 signal within the white matter of each respective lobe. CONCLUSIONS: T2 mapping analyzed using statistical parametric mapping was sensitive in patients with malformations of cortical development and acquired cerebral damage. Increased T2 signal in individual and grouped MRI-negative patients suggests that minor structural abnormalities exist in occult epileptogenic cerebral lesions.

Magnetization transfer imaging in focal epilepsy.

OBJECTIVES: To test the hypothesis that magnetization transfer imaging (MTI), analyzed on a voxel-by-voxel basis, would identify areas of abnormal magnetization transfer ratio (MTR) in patients with focal epilepsy. METHODS: The authors used MTI maps and statistical parametric mapping (SPM) to objectively compare the cerebral structures of 15 patients with malformations of cortical development (MCD), 10 with partial seizures and acquired lesions, and 42 with partial seizures and normal conventional MRI with those of 30 control subjects. RESULTS: Significant reductions of MTR were identified in all 10 patients with acquired nonprogressive cerebral lesions and partial seizures. In all, the areas of decreased MTR concurred with abnormalities identified on visual inspection of conventional MRI. In 13 of the 15 patients with MCD, SPM detected regions of significantly reduced MTR, all of which corresponded to abnormalities identified on visual inspection of conventional MRI. In addition, in both groups, there were areas that were normal on conventional imaging that demonstrated abnormal MTR. There was a significant reduction of MTR in 15 of the 42 patients with cryptogenic focal epilepsy. In all of these, the areas of reduced MTR concurred with epileptiform EEG abnormality and clinical seizure semiology. CONCLUSIONS: Magnetization transfer imaging analyzed using statistical parametric mapping was sensitive in identifying malformations of cortical development and acquired cerebral lesions. Abnormalities of magnetization transfer ratio in individual MRI-negative patients suggest that minor structural disorganization exists in occult epileptogenic cerebral lesions.

Diffusion imaging shows abnormalities after blunt head trauma when conventional magnetic resonance imaging is normal.

The investigation and management of patients after head injury must include the accurate and complete identification of cerebral damage. Using diffusion tensor imaging, abnormalities of diffusion in patients with head injuries and unremarkable MRI have been shown for the first time.

Evaluation of the accuracy of seizure descriptions by the relatives of patients with epilepsy.

The descriptions of seizures by witnesses are important in the diagnosis and classification of epileptic seizures. The aim of the study was to evaluate the accuracy of this information obtained from relatives of patients with epileptic and non-epileptic attacks. Thirty patients with epileptic or non-epileptic attacks had seizures videorecorded whilst inpatients at the Assessment and Treatment Centre of the National Society for Epilepsy and the National Hospital for Neurology and Neurosurgery, Chalfont, Buckinghamshire, UK. A relative or close friend of each patient viewed the recording and subsequently completed a structured questionnaire, testing recall of 15 separate elements of the episode. This account was compared to a definitive evaluation completed by medical staff. An accuracy of describing seizures was therefore obtained. Our results showed that there was a wide variation in the accuracy of recall with convulsive episodes described less well than non-convulsive (median accuracies 44.5 and 70%, respectively, P<0.05). Attacks in which the diagnosis had been changed, following admission, from the one obtained on history alone were particularly inaccurately described (median accuracy 26%). Elements of the questionnaire that were most inaccurately recalled were description of limb movement and post-ictal behaviour. Those most accurately described were facial appearance and vocalization. Features only present in non-epileptic attacks included reactivity to eyelash stimulation, opisthotonic posturing, flailing or protective limb movements. In conclusion, our results confirm that inaccuracy exists when witnesses describe attacks and that this may lead to errors in diagnosis and subsequent treatment.

Diffusion tensor imaging in patients with epilepsy and malformations of cortical development.

Malformations of cortical development (MCD) are a common cause of epilepsy. Studies of structural MRIs and PET data in patients with MCD have found widespread changes outside the visually identified lesions. The aim of this study was to investigate diffusion changes interictally in patients with MCD and to test the hypothesis that MCD would be associated with widespread abnormalities of diffusion. We used diffusion tensor imaging (DTI) and statistical parametric mapping (SPM) to compare objectively tissue organization in 22 patients with partial seizures and MCD, with 30 control subjects. Whole-brain DTI was acquired using echo planar imaging. Rotationally invariant anisotropy and diffusivity maps were calculated and, after normalization to Talairach space, each patient was compared with the group of control subjects using SPM. Areas of reduced anisotropy were found in 17 patients and areas of increased diffusivity in 10. Two patients had areas of increased anisotropy. There were no patients with reduced diffusivity. Areas of increased diffusivity were in general more extensive than areas of reduced anisotropy. Changes in tissue beyond the MCD, that appeared normal on conventional MRI, were found in six patients for anisotropy and nine patients for diffusivity. Both measurements showed widespread changes in tissue beyond the MCD, i.e. adding information to conventional MRI. Increased or abnormally located grey matter or pathological white matter with abnormal myelination or ectopic neurones could cause reduced anisotropy. Increased diffusivity could be caused by a defect of neurogenesis or cell loss resulting in increased extracellular space. The widespread nature of abnormalities should be considered if surgical treatment is contemplated.

Diffusion tensor imaging of cryptogenic and acquired partial epilepsies.

Current optimal MRI identifies a relevant structural abnormality in up to 80% of patients with refractory partial seizures. Identification of a structural lesion is fundamental to pre-surgical evaluation. We used diffusion tensor imaging (DTI) and statistical parametric mapping (SPM) to examine objectively the diffusion properties, and hence structural organization, of cerebral tissue in 10 patients with partial seizures and acquired lesions and 30 patients with partial seizures and normal MRI. Fractional anisotropy and mean diffusivity maps were calculated and, using SPM, individual patients were compared with a group of 30 control subjects. Diffusion tensor imaging and voxel-by-voxel statistical comparisons identified significant increases in diffusivity and significant reductions of anisotropy in all patients with acquired non-progressive cerebral lesions and partial seizures. In all of these patients, the areas of increased diffusivity, and in nine patients the areas of decreased anisotropy, concurred with abnormalities identified on visual inspection of conventional MRI. In addition, there were 10 areas which were normal on conventional imaging which exhibited abnormal anisotropy or diffusivity. Individual analyses of the 30 patients with partial seizures and normal optimal MRI identified a significant increase in diffusivity in eight of the subjects. In six of these, the areas of increased diffusivity concurred with the localization of epileptiform EEG abnormality. Analysis of anisotropy in the MRI-negative patients revealed significant differences in two patients, one of which concurred with electroclinical seizure localization. Group analysis of nine patients with normal conventional MRI and electroclinical seizure onset localizing to the left temporal region revealed a significant increase in diffusivity and a significant reduction in anisotropy within the white matter of the left temporal lobe. DTI analysed using SPM was sensitive in patients with acquired cerebral damage. Significant differences in the diffusion indices in individual MRI negative patients and the group effect in patients with left temporal lobe epilepsy suggest that minor structural disorganization exists in occult epileptogenic cerebral lesions. These techniques are promising, non-invasive imaging methods for identifying the cause of partial seizures, and can contribute to pre-surgical evaluation.

Topological analyses of the L-fucose-H+ symport protein, FucP, from Escherichia coli.

The transport of L-fucose into Escherichia coli is mediated by the L-fucose-H+ symport protein (FucP). The fucP gene has been sequenced and encodes a hydrophobic protein that contains 438 amino acid residues, with a predicted M(r) of 47,773. The hydropathic profile of FucP indicates 10 to 12 hydrophobic regions that could span the membrane as alpha-helices. A 12-helix model with the N- and C-termini located in the cytoplasm was derived from the hydropathic profile and from application of the 'positive inside' rule. This model was tested using beta-lactamase fusion technology. Analyses of 62 different FucP-beta-lactamase fusions suggested that the FucP protein crosses the cytoplasmic membrane of E. coli 12 times, with the N- and C-termini in the cytoplasm. From measurements of [14C]-L-fucose uptake, it was deduced that the last putative transmembrane region must be complete for transport activity to be retained and that the four C-terminal residues were unnecessary for transport activity. Fourier transform analyses show that all the predicted helices contain a periodicity that enables hydrophobic/hydrophilic faces to be identified; these were particularly evident in putative helices 1, 3, 4, 5, 6, 10 and 11.

Identification of a novel sugar-H+ symport protein, FucP, for transport of L-fucose into Escherichia coli.

L-Fucose (6-deoxy-L-galactose) is used as sole carbon source by many microorganisms, and its transport into Escherichia coli is mediated by an L-fucose-H+ symport activity. In order to determine the nature of a putative transporter encoded by the E. coli fucP gene and identify its protein product it was cloned downstream of the inducible T7 RNA polymerase and lambda OLPL promoters. Induction of the T7 promoter resulted in the expression of [14C]-L-fucose uptake activity and the concomitant expression of a [35S]-Met-labelled 32 kDa protein at levels too low for detection by staining with Coomassie brilliant blue or for protein sequencing. Induction of the lambda OLPL promoter caused the appearance of L-fucose-H+ symport activity and of a Coomassie brilliant blue-stained 32 kDa membrane protein expressed at high levels sufficient for identification as FucP by N-terminal protein sequencing. The FucP protein is, therefore, a sugar-H+ symporter different in amino acid sequence from any other known transporter. These and other results illustrate the general unpredictability of cloning strategies for attempting the amplified expression of membrane transport proteins.

Structural basis for the kinetic differences between flavocytochromes b2 from the yeasts Hansenula anomala and Saccharomyces cerevisiae.

To understand the structural basis for the different catalytic behaviour of the flavocytochromes b2 from Saccharomyces cerevisiae and Hansenula anomala we have cloned and sequenced the gene encoding the latter. We have compared the amino acid sequences of the mature proteins in the context of the known crystal structure of S. cerevisiae flavocytochrome b2. Overall there is 60% sequence identity, but two surface loops in particular are strikingly different in primary structure and net charge.