Biomedical subjects

S B Hong

Publications and source records attributed to S B Hong.

At least 37 records · Page 2Linked to original sources

PubMed1999

Stereochemical constraints on the substrate specificity of phosphotriesterase.

A series of achiral, chiral, and racemic mixtures of paraoxon analogues containing various combinations of methyl, ethyl, isopropyl, or phenyl substituents were synthesized as probes of the stereochemical constraints within the active site of phosphotriesterase. The kinetic constants for these paraoxon analogues with the enzyme varied significantly with the size of substituents surrounding the phosphorus center. These results indicate that binding and catalysis depend significantly on the relative size and orientation of the two subsites that must accommodate the coordination of the alkyl or aryl substituents within the enzyme active site. Individual enantiomers of paraoxon analogues were also synthesized and the stereochemical specificity for phosphotriesterase determined. In general, the kinetic constants, kcat and kcat/Km, for the (-)-enantiomers of these phosphotriesters were 1-2 orders of magnitude greater than the (+)-enantiomers. In every case, the preferred isomer is of the SP-configuration. For example, the kcat/Km for SP-(-)-ethyl phenyl p-nitrophenyl phosphate is 1.8 x 10(8) M-1 s-1 but is only 1.8 x 10(6) M-1 s-1 for the RP-(+)-isomer. These results suggest that one enantiomer is positioned for hydrolysis more favorably than the other enantiomer. The inactivation of acetylcholinesterase with the same series of organophosphate nerve agents was also measured. The stereoisomer that more rapidly inactivates human acetylcholinesterase is hydrolyzed more slowly than its enantiomer by the phosphotriesterase.

Acetylcholinesterase↗

PubMed1999

A common mutation in the methylenetetrahydrofolate reductase gene is a determinant of hyperhomocysteinemia in epileptic patients receiving anticonvulsants.

Hyperhomocysteinemia is a condition caused by both genetic and nongenetic factors. To determine whether a common methylenetetrahydrofolate reductase (MTHFR) variant is related to elevated homocysteine concentrations in epileptic patients receiving anticonvulsants, we investigated the plasma total homocysteine (tHcy) level, folate level, and MTHFR 677 C --> T mutation using a polymerase chain reaction (PCR) and restriction fragment length polymorphism analysis with HinfI digestion in 103 patients with epilepsy and 103 normal controls. The prevalence of hyperhomocysteinemia (> or = 11.4 micromol/L, 90th percentile of control group) was higher in patients than in controls (25% v 10.0%, P = .007). The homozygosity for the 677 C --> T mutation of MTHFR was associated with elevated tHcy and low folate levels. The magnitude of hyperhomocysteinemia in MTHFR TT homozygotes was more pronounced in epileptic patients than in controls (18.2 +/- 1.6 v 9.1 +/- 1.2 micromol/L, P = .04). In epileptic patients, hyperhomocysteinemia was more frequent in MTHFR TT genotypes versus CT or CC genotypes (58% v 17% and 16%, P < .001). Multiple logistic regression analysis showed that MTHFR TT genotype was an independent predictor of hyperhomocysteinemia in epileptic patients receiving anticonvulsants (phenytoin and carbamazepine but not valproic acid), suggesting that gene-drug interactions induce hyperhomocysteinemia. These findings indicate that epileptic patients receiving anticonvulsants may have a higher folate requirement to maintain a normal tHcy level, especially homozygotes for MTHFR 677 C --> T mutation.

Adolescent↗

PubMed1999

Molecular characterization of a tomato endo-beta-1,4-glucanase gene expressed in mature pistils, abscission zones and fruit.

A cDNA (TAC1) and genomic clone (cel5) encoding an endo-beta-1,4-glucanase (EGase) were identified from tomato (Lycopersicon esculentum Mill., cv. Rutgers). The cel5 gene is expressed in pistils, flower pedicel and leaf abscission zones, and ripening fruit. The genomic sequence includes a 22 bp 5' upstream sequence that is conserved in a closely related peach EGase gene, ppEG1.

Amino Acid Sequence↗

PubMed1999

Partial seizures manifesting as apnea only in an adult.

PURPOSE: Although several cases of apneic seizures have been reported in neonates, epileptic seizures presenting as apnea only in adults are very rare. We present a case report of a 19-year-old man with viral encephalitis and frequent episodes of apneic seizures. METHODS: Prolonged electroencephalograms (EEGs), respiratory monitorings, and imaging including ictal-interictal subtraction single photon emission computed tomography (SPECT) coregistered with magnetic resonance imaging (MRI) were performed. RESULTS: Ictal EEGs recorded during apneic episodes showed repetitive sharp waves or rhythmic theta activity arising from the left or right independent bitemporal region. Ictal SPECT was performed during one episode of apnea that showed ictal EEG discharges arising from the left posterior temporal area. Ictal-interictal subtraction SPECT coregistered with MRI revealed that the seizures originated from the left, posterior, midlateral temporal cortex. CONCLUSIONS: Previous studies with ictal EEG or brain stimulation suggest that apneic seizures might be mediated through the limbic and associated cortical systems. Our study reports on a very rare case of partial seizures with apnea only in an adult patient and is supported by ictal EEG and ictal-interictal subtraction SPECT coregistered with MRI.

Adult↗

PubMed1999

White-matter change in mesial temporal sclerosis: correlation of MRI with PET, pathology, and clinical features.

PURPOSE: To assess the magnetic resonance imaging (MRI), positron emission tomography (PET), pathology, and clinical findings of patients with the MRI feature of white-matter change (WMC) in the anterior temporal lobe. METHODS: Fifty-six patients with pathologically proven mesial temporal sclerosis were included in this study. MRI and 18F-2-deoxyglucose-(FDG) PET images were obtained before surgery in all patients. The patients were divided into two groups according to the presence of WMC on their MRI. WMC consists of an indistinct gray-white matter demarcation and an increased signal intensity of the anterior temporal lobe on T2-weighted images. The two groups were then compared in terms of MRI, PET, pathology, and clinical features. RESULTS: The MRI feature of WMC was observed in 18 (32%) of the 56 patients. PET images of those patients revealed more severe hypometabolism of the ipsilateral temporal lobes (p< 0.05). In terms of histologic findings, larger numbers of heterotopic neurons were observed in the anterior temporal lobe white matter of these patients who also shared the following clinical features: earlier seizure onset, frequent history of febrile convulsions, and favorable surgical outcomes. CONCLUSIONS: The MRI feature of WMC is an additive sign for correct seizure lateralization and may be related to a favorable surgical outcome in patients with temporal lobe epilepsy.

Adolescent↗

PubMed1998

Hydrolysis of phosphodiesters through transformation of the bacterial phosphotriesterase.

The phosphotriesterase from Pseudomonas diminuta catalyzes the hydrolysis of a wide array of phosphotriesters and related phosphonates, including organophosphate pesticides and military nerve agents. It has now been shown that this enzyme can also catalyze the hydrolysis of phosphodiesters, albeit at a greatly reduced rate. However, the enzymatic hydrolysis of ethyl-4-nitrophenyl phosphate (compound I) by the wild-type enzyme was >10(8) times faster than the uncatalyzed reaction (kcat = 0.06 s-1 and Km = 38 mM). Upon the addition of various alkylamines to the reaction mixture, the kcat/Km for the phosphodiester (compound I) increased up to 200-fold. Four mutant enzymes of the phosphotriesterase were constructed in a preliminary attempt to improve phosphodiester hydrolysis activity of the native enzyme. Met-317, which is thought to reside in close proximity to the pro-S-ethoxy arm of the paraoxon substrate, was mutated to arginine, alanine, histidine, and lysine. These mutant enzymes showed slight improvements in the catalytic hydrolysis of organophosphate diesters. The M317K mutant enzyme displayed the most improvement in catalytic activity (kcat = 0.34 s-1 and Km = 30 mM). The M317A mutant enzyme catalyzed the hydrolysis of the phosphodiester (compound I) in the presence of alkylamines up to 200 times faster than the wild-type enzyme in the absence of added amines. The neutralization of the negative charge on the oxygen atom of the phosphodiester by the ammonium cation within the active site is thought to be responsible for the rate enhancement by these amines in the hydrolytic reaction. These results demonstrate that an active site optimized for the hydrolysis of organophosphate triesters can be made to catalyze the hydrolysis of organophosphate diesters.

Amines↗

PubMed1998

Cloning and characterization of the full-length cDNA and genomic sequences encoding murine acid ceramidase.

The full-length cDNA and genomic sequences encoding murine acid ceramidase (AC; E.C. 3.5.1.23) have been isolated and characterized. The 2176-bp cDNA was approximately 80% identical to the human cDNA (Koch et al., 1996) and predicted a 394-amino-acid polypeptide that was approximately 90% identical to the human protein. A fluorescence-based assay system was developed to determine AC enzymatic activity, and transfection of COS-1 cells with the full-length mouse cDNA led to increased AC activity, demonstrating its functionality. The murine AC gene, which spanned approximately 38 kb, consisted of 14 exons separated by 13 introns. The exons ranged in size from 46 to 1038 bp and were flanked by exon/intron junctions that adhered closely to known donor and acceptor splice site consensus sequences. Exon 1 encoded the putative translation start site and the signal peptide region, while exon 14 encoded the carboxy end of the AC polypeptide and all of the 3' untranslated region. Sequence analysis of a 497-bp region upstream from the first in-frame ATG revealed several features of a housekeeping promoter, as well as several tissue-specific and/or hormone-inducible regulatory sites. Insertion of this sequence into a chloramphenicol acyltransferase (CAT) expression vector led an approximately fivefold increase in CAT activity after transfection into NIH3T3 cells. Northern blot analysis and enzymatic assays also were carried out on various murine tissues to examine AC expression. Of the tissues studied, the highest AC activity and mRNA levels were found in the kidney, followed by the brain; almost no AC activity or mRNA was found in the testis or skeletal muscle. These latter studies provided clear evidence that despite the housekeeping function of AC, its expression was tissue-specific.

Acid Ceramidase↗

PubMed1998

Genomic organization of six tomato polygalacturonases and 5' upstream sequence identity with tap1 and win2 genes.

Recently, three polygalacturonase (PG) cDNAs (TAPG1, TAPG2, and TAPG4) were identified in a library prepared from tomato (Lycopersicon esculentum cv. Rutgers) leaf abscission zones. Genomic clones encoding these three cDNAs have been identified. Moreover, the genomic clones include three additional PG genes, TPG3, TAPG5 and TPG6, which have not been previously reported. A transcript for TAPG5 was detected in the RNA from leaf and flower abscission zones; however, transcripts for TPG3 and TPG6 were not. DNA sequence analysis revealed that TAPG1, TAPG2, and TPG3 are linked in a close tandem array. TAPG4, TAPG5 and TPG6 are also closely linked to each other but in divergent and inverted orientations and are not closely linked to TAPG1, TAPG2, or TPG3. TAPG4, TAPG5 and TPG6 map to the middle of chromosome 12. TPG6 contains two introns. The other five PG genes include four exons and three introns. The relative positions of introns 1 and 2 are shared by all six PG genes. The position of intron 3 is conserved in the other five. The structure of the tomato fruit PG gene, which contains 8 introns, is compared with that of the six PG genes described above. Of interest is an approximately 300 bp inverted repeat found in TAPG1, TAPG2 and TAPG4 that shares significant sequence identity with sequence in the first intron of the tomato anionic peroxidase gene, tap1. RNA blot analysis indicates that the transcript for an anionic peroxidase increases during abscission. In addition, a 250 bp sequence found in TPG3 shares high sequence identity with a 5' upstream region in a wound-induced win2 gene from potato. Potential sites of transcriptional regulation in these genes are discussed.

Base Sequence↗

PubMed1998

Ipsilateral neglect during intracarotid amobarbital test.

Neglect usually occurs in the space contralateral to brain injury. Recent studies describe ipsilateral neglect (IN) whereby patients with right hemisphere injury misbisect lines to the left of midpoint. IN usually develops after contralateral neglect (CN) resolves. We observed whether IN occurs during intracarotid amobarbital infusion. After clinical testing but before resolution of barbiturate effect, 20 right-handed subjects bisected lines until baseline performance returned. More than half (12 of 20) showed transient CN. IN occurred in 40% (8 of 20) of patients, always during the recovery stage of anesthesia, and most frequently followed initial CN.

Adolescent↗

PubMed1998

Comparison of corneal centering in photorefractive keratectomy.

The present study compares three centering methods for excimer laser photorefractive keratectomy (PRK. VISX 20/20) by analyzing the corneal topography. The subjects were grouped according to three different centering methods used in the procedure: an ablation using a light reflex from the patient's cornea pursued by both eyes of the surgeon (Group 1, n = 49); an ablation using a red light reflex from the patient's cornea pursued by the surgeon's left eye only while the right eye remained closed (Group 2, n = 27); an ablation using the patient's center of the pupil pursued by the surgeon's left eye only while the right eye remained closed (Group 3, n = 21). The mean distance from the center of ablation zone to the center of the pupil were; 0.69 +/- 0.45 mm for Group 1, 1.05 +/- 0.48 mm for Group 2 and 0.63 +/- 0.28 mm for Group 3. The degree of deviation in Group 2 was significantly greater than in Group 1 or Group 3. The deviation was greater in the right eyes than the left eyes in Group 2 only. The decentration of the right eye in Group 2 was due to angle Kappa with misalignment of the fixation light and viewing tube containing reticule.

Adult↗

PubMed1997

Identification of the transcription termination site of the mouse nkx-1.2 gene: involvement of sequence-specific factors.

We have identified a transcription termination site in the 3' flanking region of the mouse nkx-1.2 gene. A downstream transcription regulatory element in the mouse nkx-1.2 gene was characterized by transferring its 3'-fragment into a chloramphenicol acetyl transferase (CAT) expression vector. Analysis of recombinant plasmids transfected into mouse NIH3T3 cells by CAT assay showed the possible region of regulation. There were two direct repeat structures containing poly(dG-dT) x poly(dC-dA) sequences (GT repeats) in this region. The precise location of transcription termination was mapped by nuclease S1 analysis of the transcripts from recombinant plasmids transfected into COSM6 cells. It was approximately 20 nucleotides upstream of the first GT repeat within the 5' sequences of the first element of the two direct repeats. Gel mobility shift assay and footprinting analysis demonstrated that nuclear DNA binding proteins bound specifically to the sequences where the termination occurred as well as the other sequences in the second element of the direct repeats. Southwestern analysis showed that 90-, 54-, 36- and 15-kDa nuclear proteins bound to the region of the termination. It is possible that one or more of those proteins are involved in blocking the elongation of the mouse nkx-1.2 gene transcript and then result in termination.

3T3 Cells↗

PubMed1997

Mechanism-based inhibitors for the inactivation of the bacterial phosphotriesterase.

1-Bromovinyl (I), Z-2-bromovinyl (II), 1,2-dibromoethyl (III), and a series of 4-(halomethyl)-2-nitrophenyl (IVa-c) diethyl phosphate esters were examined as substrates and mechanism-based inhibitors for the bacterial phosphotriesterase. All of these compounds were found to act as substrates for the enzyme. Inhibitor I rapidly inactivated the enzyme within 1 min, giving a partition ratio of 230. The newly formed covalent adduct with inhibitor I was susceptible to hydrolysis at elevated values of pH and dissociation by NH2OH. Azide was not able to protect the enzyme from inactivation with inhibitor I, implying that the reactive species was not released into solution prior to the inactivation event. The reactive species was proposed to be either an acyl bromide or a ketene intermediate formed by the enzymatic hydrolysis of inhibitor I. Compounds II and III were shown to be relatively poor substrates of phosphotriesterase and they did not induce any significant inactivation of the enzyme. The inhibitor, 4-(bromomethyl)-2-nitrophenyl diethyl phosphate (IVa), was found to irreversibly inactivate the enzyme with a KI = 7.9 mM and kinact = 1. 2 min-1 at pH 9.0. There was no effect on the rate of inactivation upon the addition of the exogenous nucleophiles, azide, and NH2OH. The species responsible for the covalent modification of the enzyme by IVa was most likely a quinone methide formed by the elimination of bromide from the phenolic intermediate. NMR experiments demonstrated that the quinone methide did not accumulate in solution. The chloro (IVb) and fluoro (IVc) analogues did not inactivate the enzyme. These results suggest that the elimination of the halide ion from the phenolic intermediate largely determines the partition ratio for inactivation.

Aryldialkylphosphatase↗

PubMed1997

A T-DNA gene required for agropine biosynthesis by transformed plants is functionally and evolutionarily related to a Ti plasmid gene required for catabolism of agropine by Agrobacterium strains.

The mechanisms that ensure that Ti plasmid T-DNA genes encoding proteins involved in the biosynthesis of opines in crown gall tumors are always matched by Ti plasmid genes conferring the ability to catabolize that set of opines on the inducing Agrobacterium strains are unknown. The pathway for the biosynthesis of the opine agropine is thought to require an enzyme, mannopine cyclase, coded for by the ags gene located in the T(R) region of octopine-type Ti plasmids. Extracts prepared from agropine-type tumors contained an activity that cyclized mannopine to agropine. Tumor cells containing a T region in which ags was mutated lacked this activity and did not contain agropine. Expression of ags from the lac promoter conferred mannopine-lactonizing activity on Escherichia coli. Agrobacterium tumefaciens strains harboring an octopine-type Ti plasmid exhibit a similar activity which is not coded for by ags. Analysis of the DNA sequence of the gene encoding this activity, called agcA, showed it to be about 60% identical to T-DNA ags genes. Relatedness decreased abruptly in the 5' and 3' untranslated regions of the genes. ags is preceded by a promoter that functions only in the plant. Expression analysis showed that agcA also is preceded by its own promoter, which is active in the bacterium. Translation of agcA yielded a protein of about 45 kDa, consistent with the size predicted from the DNA sequence. Antibodies raised against the agcA product cross-reacted with the anabolic enzyme. These results indicate that the agropine system arose by a duplication of a progenitor gene, one copy of which became associated with the T-DNA and the other copy of which remained associated with the bacterium.

Agrobacterium tumefaciens↗

PubMed1997

Inhibitors directed towards the binuclear metal center of phosphotriesterase.

The potential roles in binding and catalysis for the binuclear metal center found within bacterial phosphotriesterase were evaluated by characterization of the inhibitory properties of 26 substrate and product mimetics. Phosphonates bearing monofluoro, difluoro, or hydroxyl substituents at the methylene position were found to be noncompetitive inhibitors with Ki values ranging from 0.6-9 mM versus the substrate paraoxon. Phosphoramidates did not significantly inhibit the enzyme. Diethyl phosphate and diethyl dithiophosphate inhibited the Cd-substituted enzyme with Ki values of 10 and 130 microM, respectively. The most effective inhibitor for either the cadmium or zinc substituted enzyme was found to be diethyl thiomethylphosphonate. The competitive inhibition constants for this compound were found to be 60 nM and 2.8 microM for the cadmium- and zinc-substituted enzyme, respectively. The tight binding is attributed to chelation of both metal ions simultaneously.

Aryldialkylphosphatase↗

PubMed1996

Metal-substrate interactions facilitate the catalytic activity of the bacterial phosphotriesterase.

The bacterial phosphotriesterase from Pseudomonas diminuta is a zinc metalloenzyme which catalyzes the hydrolysis of a variety of organophosphorus nerve agents with high efficiency. The active site of the enzyme consists of a coupled binuclear metal center embedded within a cluster of histidine residues. Potential protein-substrate interactions at the active site were probed by a systematic variation of metal identity, leaving group potential, phosphate host, and amino acid replacement. In order to determine the roles of these metal ions in binding and catalysis, the microscopic rate constants and kinetic parameters were obtained with various divalent cations. The divalent cations that were utilized in this investigation consisted of Co2+, Ni2+, Cd2+, Zn2+, Mn2+, and the mixed-metal Zn2+/Cd2+ hybrid. The leaving group potential and phosphate host were varied by altering the pKa of the departing substituted phenol or thiophenol in either a diethyl phosphate or a diethyl thiophosphate substrate. The Brønsted plots for the nonenzymatic hydroxide catalyzed hydrolysis of these substrates showed a linear dependence between the pseudo-first-order rate constant and the pKa of the leaving group. Enzymatic activities of the wild-type enzyme with these same substrates varied by over 7 orders of magnitude over the entire experimental pKa range (4.1-10.3), and the corresponding Brønsted plots were nonlinear. Those substrates with leaving groups with high pKa values were limited by the rate of bond cleavage while those substrates having leaving groups with low pKa values were limited by a conformational change or binding event. Thiophosphate substrates having leaving groups with high pKa values were better substrates than the corresponding phosphate analogues. These results are consistent with the direct coordination of one or both metal ions with the phosphoryl sulfur or oxygen atom of the substrate. A large dependence of the rate on the leaving group rules out the possibility of protonation of the leaving group or electrostatic interaction of the leaving group oxygen (or sulfur) with a metal ion or cationic group at the active site. The large differences in the size of the beta lg over the range of metal ions utilized by the enzyme indicate that the metal ions polarize the phosphoryl group and alter the structure of the transition state. The values of V/K(m) for the enzyme-catalyzed hydrolysis for a series of substituted thiophenol analogues were 10(2)-10(3)-fold smaller than those obtained for the hydrolysis of the corresponding phenolic substrates, suggesting that the bulkier sulfur substituent in the leaving group may induce conformational restrictions at the active site. With the zinc-substituted H201N mutant enzyme, there was a large decrease in the rate of phosphotriester hydrolysis but essentially no change in the rate of thiophosphotriester hydrolysis relative to the values observed for the zinc-substituted wild-type enzyme. These results suggest that a direct perturbation in the ligand structure of the binuclear metal center induces alterations in the mechanism of substrate hydrolysis.

Aryldialkylphosphatase↗

PubMed1996

Purification and characterization of catabolic mannopine cyclase encoded by the Agrobacterium tumefaciens Ti plasmid pTi15955.

Catabolic mannopine (MOP) cyclase encoded by certain Agrobacterium Ti and Ri plasmids lactonizes MOP to agropine (AGR). The enzyme, purified to homogeneity from a recombinant clone, has a molecular mass of 45 kDa as measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and size exclusion chromatography. The enzyme catalyzed the lactonization of MOP to AGR without the need for any cofactors. The enzyme also converted AGR to MOP with the lactonizing activity being predominant over the reverse reaction. MOP cyclase is specific for imine conjugates of D-hexose and L-glutamine and was not inhibited by sugars or amino acids. The enzyme lactonized deoxyfructosyl glutamine, a natural intermediate of MOP synthesis and catabolism, to a product indistinguishable from chrysopine, a newly discovered crown gall opine. The enzyme also lactonized N-l-(1,2-dideoxy-D-mannityl)-L-glutamine, indicating that a hydroxyl group at carbon atom 2 of the sugar moiety is not required for the enzymatic reaction.

Agrobacterium tumefaciens↗

PubMed1994

Functional role of the Ti plasmid-encoded catabolic mannopine cyclase in mannityl opine catabolism by Agrobacterium spp.

Catabolic mannopine (MOP) cyclase encoded by Ti or Ri plasmids lactonizes MOP to agropine (AGR). The gene of the octopine-type Ti plasmid pTi15955 encoding the catabolic MOP cyclase enzyme previously was localized to a 1.6-kb segment within a cosmid clone, pYDH208. A subclone containing only this region complemented the AGR catabolism-negative phenotype conferred by a derivative of the octopine-type plasmid pTiB6S3 containing a Tn7 insertion in the region encoding the MOP cyclase enzyme. Uptake assays of strains harboring pRiA4 or pArA4a, along with complementation analyses, indicate that MOP cyclase is not sufficient for catabolism of AGR but that the strains must also express an AGR transport system. To determine the requirement for MOP cyclase in opine catabolism unequivocally, a site-specific, nonpolar deletion mutation abolishing only MOP cyclase activity was introduced into pYDH208, a cosmid clone that confers utilization of MOP, AGR, and mannopinic acid (MOA). Strains harboring this MOP cyclase-negative mutant clone, pYDPH208, did not utilize AGR but continued to utilize MOP. Growth on AGR was restored in this strain upon introduction of clones encoding the pTi15955-derived catabolic or anabolic MOP cyclase genes. The induction pattern of MOA catabolism shown by strain NT1 harboring the MOP cyclase-deficient pYDPH208 suggests that AGR is converted into MOP by MOP cyclase and that MOP, but not AGR, induces catabolism of MOA. Genetic and biochemical analyses of MOP and AGR metabolism suggest that only the conversion of AGR to MOP is directly involved in catabolism of AGR, even though the reaction catalyzed by MOP cyclase predominantly lies in the lactonization of MOP to AGR.

Genetic Complementation Test↗

PubMed1994

Amnesia syndrome following left anterior thalamic infarction; with intrahemispheric and crossed cerebro-cerebellar diaschisis on brain SPECT.

We report a 61-year-old right-handed man developing disturbance of memory after a discrete thalamic infarction. Neuropsychological assessment revealed deficits in memory with retrograde and anterograde components, especially for verbal material. Brain MRI showed a left anterior thalamic infarction with normal angiographic findings. Despite the small lesion in the thalamus, he showed prolonged memory disturbance and a Brain SPECT image revealed decreased uptake in the ipsilateral fronto-temporo-parietal cortex and contralateral cerebellum. This diaschisis, a phenomenon caused by disconnection of the neural pathway helped us to evaluate the functional state of the patient and this imaging technique was valuable for obtaining to get more information for the evaluation of the neurological state and neuronal connections. In conclusion our findings correspond well with the understanding of amnesia as a disconnection syndrome because of the evidence of diaschisis on the Brain SPECT image.

Amnesia↗