A comprehensive genetic map of the human genome based on 5,264 microsatellites

The great increase in successful linkage studies in a number of higher eukaryotes during recent years has essentially resulted from major improvements in reference genetic linkage maps, which at present consist of short tandem repeat polymorphisms of simple sequences or microsatellites. We report here the last version of the Généthon human linkage map. This map consists of 5,264 short tandem (AC/TG)n repeat polymorphisms with a mean heterozygosity of 70%. The map spans a sex-averaged genetic distance of 3,699 cM and comprises 2,335 positions, of which 2,032 could be ordered with an odds ratio of at least 1,000:1 against alternative orders. The average interval size is 1.6 cM; 59% of the map is covered by intervals of 2 cM at most and 1% remains in intervals above 10 cM.

Spastin, a new AAA protein, is altered in the most frequent form of autosomal dominant spastic paraplegia

Autosomal dominant hereditary spastic paraplegia (AD-HSP) is a genetically heterogeneous neurodegenerative disorder characterized by progressive spasticity of the lower limbs. Among the four loci causing AD-HSP identified so far, the SPG4 locus at chromosome 2p2-1p22 has been shown to account for 40-50% of all AD-HSP families. Using a positional cloning strategy based on obtaining sequence of the entire SPG4 interval, we identified a candidate gene encoding a new member of the AAA protein family, which we named spastin. Sequence analysis of this gene in seven SPG4-linked pedigrees revealed several DNA modifications, including missense, nonsense and splice-site mutations. Both SPG4 and its mouse orthologue were shown to be expressed early and ubiquitously in fetal and adult tissues. The sequence homologies and putative subcellular localization of spastin suggest that this ATPase is involved in the assembly or function of nuclear protein complexes.

A human homologue of the Drosophila eyes absent gene underlies branchio-oto-renal (BOR) syndrome and identifies a novel gene family

A candidate gene for Branchio-Oto-Renal (BOR) syndrome was identified at chromosome 8q13.3 by positional cloning and shown to underlie the disease. This gene is a human homologue of the Drosophila eyes absent gene (eya), and was therefore called EYA1. A highly conserved 271-amino acid C-terminal region was also found in the products of two other human genes (EYA2 and EYA3), demonstrating the existence of a novel gene family. The expression pattern of the murine EYA1 orthologue, Eya1, suggests a role in the development of all components of the inner ear, from the emergence of the otic placode. In the developing kidney, the expression pattern is indicative of a role for Eya1 in the metanephric cells surrounding the 'just-divided' ureteric branches.

Mechanisms of evolution in Rickettsia conorii and R. prowazekii

Rickettsia conorii is an obligate intracellular bacterium that causes Mediterranean spotted fever in humans. We determined the 1,268,755-nucleotide complete genome sequence of R. conorii, containing 1374 open reading frames. This genome exhibits 804 of the 834 genes of the previously determined R. prowazekii genome plus 552 supplementary open reading frames and a 10-fold increase in the number of repetitive elements. Despite these differences, the two genomes exhibit a nearly perfect colinearity that allowed the clear identification of different stages of gene alterations with gene remnants and 37 genes split in 105 fragments, of which 59 are transcribed. A 38-kilobase sequence inversion was dated shortly after the divergence of the genus.

Progress in allogeneic bone marrow and peripheral blood stem cell transplantation for multiple myeloma: a comparison between transplants performed 1983-93 and 1994-98 at European Group for Blood and Marrow Transplantation centres

Out of 690 allogeneic matched sibling donor transplants for multiple myeloma reported to the European Group for Blood and Marrow Transplantation (EBMT) registry, 334 were performed during the period 1983-93 (all with bone marrow) and 356 during 1994-98 [223 with bone marrow and 133 with peripheral blood stem cells (PBSCs)]. The median overall survival was 10 months for patients transplanted during the earlier time period and 50 months for patients transplanted with hone marrow during the later period. The use of PBSCs was associated with earlier engraftment but no significant survival benefit compared to bone marrow transplants during the same time period. The improvement in survival since 1994 with the result of a significant reduction in transplant-related mortality, which was 38%, 21% and 25% at 6 months and 46%, 30% and 37% at 2 years during the earlier period, and the later period with bone marrow and PBSCs respectively. Reasons for the reduced transplant-related mortality appeared to be fewer deaths owing to bacterial and fungal infections and interstitial pneumonitis, in turn a result of earlier transplantation and less prior chemotherapy. Better supportive treatment and more frequent use of cytokines may also play a role. The improvement in survival was not directly related to the increased use of PBSCs.

Comparison of EDTA and EDDS as potential soil amendments for enhanced phytoextraction of heavy metals

Phytoextraction has been proposed as an alternative remediation technology for soils polluted with heavy metals or radionuclides, but is generally conceived as too slow working. Enhancing the accumulation of trace pollutants in harvestable plant tissues is a prerequisite for the technology to be practically applicable. The chelating aminopolycarboxylic acid, ethylene diamine tetraacetate (EDTA), has been found to enhance shoot accumulation of heavy metals. However, the use of EDTA in phytoextraction may not be suitable due to its high environmental persistence, which may lead to groundwater contamination. This paper aims to assess whether ethylene diamine disuccinate (EDDS), a biodegradable chelator, can be used for enhanced phytoextraction purposes. A laboratory experiment was conducted to examine mobilisation of Cd, Cu, Cr, Ni, Pb and Zn into the soil solution upon application of EDTA or EDDS. The longevity of the induced mobilisation was monitored for a period of 40 days after application. Estimated effect half lives ranged between 3.8 and 7.5 days for EDDS, depending on the applied dose. The minimum observed effect half life of EDTA was 36 days, while for the highest applied dose no decrease was observed throughout the 40 day period of the mobilisation experiment. Performance of EDTA and EDDS for phytoextraction was evaluated by application to Helianthus annuus. Two other potential chelators, known for their biodegradability in comparison to EDTA, were tested in the plant experiment: nitrilo acetic acid (NTA) and citric acid. Uptake of heavy metals was higher in EDDS-treated pots than in EDTA-treated pots. The effects were still considered insufficiently high to consider efficient remediation. This may be partly due to the choice of timing for application of the soil amendment. Fixing the time of application at an earlier point before harvest may yield better results. NTA and citric acid induced no significant effects on heavy metal uptake.

The complete genome sequence of the murine respiratory pathogen Mycoplasma pulmonis

Mycoplasma pulmonis is a wall-less eubacterium belonging to the Mollicutes (trivial name, mycoplasmas) and responsible for murine respiratory diseases. The genome of strain UAB CTIP is composed of a single circular 963 879 bp chromosome with a G + C content of 26.6 mol%, i.e. the lowest reported among bacteria, Ureaplasma urealyticum apart. This genome contains 782 putative coding sequences (CDSs) covering 91.4% of its length and a function could be assigned to 486 CDSs whilst 92 matched the gene sequences of hypothetical proteins, leaving 204 CDSs without significant database match. The genome contains a single set of rRNA genes and only 29 tRNAs genes. The replication origin oriC was localized by sequence analysis and by using the G + C skew method. Sequence polymorphisms within stretches of repeated nucleotides generate phase-variable protein antigens whilst a recombinase gene is likely to catalyse the site-specific DNA inversions in major M.pulmonis surface antigens. Furthermore, a hemolysin, secreted nucleases and a glyco-protease are predicted virulence factors. Surprisingly, several of the genes previously reported to be essential for a self-replicating minimal cell are missing in the M.pulmonis genome although this one is larger than the other mycoplasma genomes fully sequenced until now.

Factors related to hydrocephalus after aneurysmal subarachnoid hemorrhage

OBJECTIVE

The purpose of this study was to identify factors predictive of shunt-dependent hydrocephalus among patients with aneurysmal subarachnoid hemorrhage. The data can be used to predict which patients in this group have a high probability of requiring permanent cerebrospinal fluid diversion.

METHODS

Seven hundred eighteen patients with aneurysmal subarachnoid hemorrhage who were treated between 1990 and 1999 were retrospectively studied, to identify factors contributing to shunt-dependent hydrocephalus. With these data, a stepwise logistic regression procedure was used to determine the effect of each variable on the development of hydrocephalus and to create a scoring system.

RESULTS

Overall, 152 of the 718 patients (21.2%) underwent shunting procedures for treatment of hydrocephalus. Four hundred seventy-nine of the patients (66.7%) were female. Of the factors investigated, the following were associated with shunt-dependent hydrocephalus, as determined with a variety of statistical methods: 1) increasing age (P < 0.001), 2) female sex (P = 0.015), 3) poor admission Hunt and Hess grade (P < 0.001), 4) thick subarachnoid hemorrhage on admission computed tomographic scans (P < 0.001), 5) intraventricular hemorrhage (P < 0.001), 6) radiological hydrocephalus at the time of admission (P < 0.001), 7) distal posterior circulation location of the ruptured aneurysm (P = 0.046), 8) clinical vasospasm (P < 0.001), and 9) endovascular treatment (P = 0.013). The presence of intracerebral hematomas, giant aneurysms, or multiple aneurysms did not influence the development of shunt-dependent hydrocephalus.

CONCLUSION

The results of this study can help identify patients with a high risk of developing shunt-dependent hydrocephalus. This may help neurosurgeons expedite treatment, may decrease the cost and length of hospital stays, and may result in improved outcomes.

Spectrum of SPG4 mutations in autosomal dominant spastic paraplegia

Autosomal dominant hereditary spastic paraplegia (AD-HSP) is a group of genetically heterogeneous neurodegenerative disorders characterized by pro- gressive spasticity of the lower limbs. Five AD-HSP loci have been mapped to chromosomes 14q, 2p, 15q, 8q and 12q. The SPG4 locus at 2p21-p22 has been shown to account for approximately 40% of all AD-HSP families. SPG4 encoding spastin, a putative nuclear AAA protein, has recently been identified. Here, sequence analysis of the 17 exons of SPG4 in 87 unrelated AD-HSP patients has resulted in the detection of 34 novel mutations. These SPG4 mutations are scattered along the coding region of the gene and include all types of DNA modification including missense (28%), nonsense (15%) and splice site point (26.5%) mutations as well as deletions (23%) and insertions (7.5%). The clinical analysis of the 238 mutation carriers revealed a high proportion of both asymptomatic carriers (14/238) and patients unaware of symptoms (45/238), and permitted the redefinition of this frequent form of AD-HSP.

Perlecan, the major proteoglycan of basement membranes, is altered in patients with Schwartz-Jampel syndrome (chondrodystrophic myotonia)

Schwartz-Jampel syndrome (SJS1) is a rare autosomal recessive disorder characterized by permanent myotonia (prolonged failure of muscle relaxation) and skeletal dysplasia, resulting in reduced stature, kyphoscoliosis, bowing of the diaphyses and irregular epiphyses. Electromyographic investigations reveal repetitive muscle discharges, which may originate from both neurogenic and myogenic alterations. We previously localized the SJS1 locus to chromosome 1p34-p36.1 and found no evidence of genetic heterogeneity. Here we describe mutations, including missense and splicing mutations, of the gene encoding perlecan (HSPG2) in three SJS1 families. In so doing, we have identified the first human mutations in HSPG2, which underscore the importance of perlecan not only in maintaining cartilage integrity but also in regulating muscle excitability.

Use of etomidate, temporary arterial occlusion, and intraoperative angiography in surgical treatment of large and giant cerebral aneurysms

The operative management of large and giant aneurysms is complicated by their typically atheromatous and thick walls, frequent intramural thrombosis with calcification, and broad-based necks that often incorporate perforating and other vital vessels. Not infrequently, it is necessary to at least focally arrest the intracranial circulation and open or excise these aneurysms to facilitate vascular reconstruction. This maneuver, in patients whose disease processes have destroyed autoregulatory function or who have inadequate sources of anatomical collateral supply, may cause the threshold for permanent ischemic injury to be exceeded. The authors have recently treated 14 such patients while under electroencephalographic monitoring to document electrical burst suppression induced by the administration of etomidate, followed by temporary clipping to permit vascular repair and intraoperative angiography to document patency of parent arteries. Up to 60 minutes of internal carotid artery occlusion, 35 minutes of middle cerebral artery occlusion, 19 minutes of upper basilar artery occlusion, and 4 1/2 minutes of lower basilar artery occlusion have been well tolerated using this protocol. In such situations, etomidate may be effective in protecting the cerebral circulation without the detrimental cardiotoxicity observed with protective doses of barbiturates.

Treatment of dural sinus thrombosis using selective catheterization and urokinase

Thrombosis of the cerebral dural venous sinuses, cortical draining veins, and deep cerebral veins is a rare clinical finding. Because of its low incidence and multiple etiologies, the optimum therapy for this condition will only be elucidated by a multicenter, randomized prospective study. At our institution, we favor early and aggressive management of cerebral venous sinus thrombosis with transfemoral, venous intradural infusions of the fibrinolytic agent urokinase. To date, treatment of only 13 patients using this technique has been reported in the English literature. This report adds 12 more such treated patients. Despite the presence of preinfusion infarcts in 5 patients, four of which were hemorrhagic, we incurred no major therapeutic morbidity. Functional sinus patency was achieved in 11 of 12 patients, with our only true failure occurring in an individual with symptoms of at least 2 months' duration. Good to excellent clinical outcome was achieved in 10 of 11 patients (one newborn had inadequate follow-up).

Complications of preoperative embolization of cerebral arteriovenous malformations

Object. Preoperative embolization is viewed by the authors as a useful adjunct in the surgical management of cerebral arteriovenous malformations (AVMs). This study was performed to determine the rate of significant complication in patients undergoing this procedure.

Methods. Demographic, anatomical, and procedure data were collected prospectively. The treating physician reported complications. In addition, a review of medical records including procedure reports, operative reports, and discharge summaries was performed. Univariate statistical analysis was performed to determine if any of the variables was predictive of a poor outcome of embolization (death or permanent neurological deficit).

Endovascular procedures for embolization were performed 339 times in 201 patients during an 11-year period. Female patients comprised 53.7% of the study group and 85.6% of the AVMs were supratentorial. Embolization was performed using polyvinyl alcohol particles, N-butyl cyanoacrylate, detachable coils, and/or the liquid polymer Onyx. Analyzed by procedure, a poor result of embolization occurred in 7.7%. Analyzed by patient, 11% died or had a permanent neurological deficit as a result of the embolization. None of the demographic, anatomical, or procedure variables identified were predictive of a poor outcome.

Conclusions. Preoperative embolization may gradually reduce flow to an AVM, reduce intraoperative blood loss, and reduce operative time. The risks of this procedure, however, are not insignificant and must be considered in planning treatment for patients with AVMs.

Clustering of mutations responsible for branchio-oto-renal (BOR) syndrome in the eyes absent homologous region (eyaHR) of EYA1

Branchio-oto-renal (BOR) syndrome is an autosomal dominant disorder, characterised by the association of branchial, otic and renal anomalies with variable degrees of severity. We have recently identified EYA1 , a human homologue of the Drosophila eyes absent gene, as the gene underlying this syndrome. The products of both genes share a highly conserved 271 amino acid C-terminal region (eyaHR). The eyaHR was also found in the products of two other human genes (EYA2 and EYA3), demonstrating the existence of a novel gene family. We report here on the complete genomic structure of EYA1. This gene consists of 16 coding exons and extends over 156 kb. It encodes various alternatively spliced transcripts differing only in their 5' regions. Sequence analysis of the entire EYA1 coding region was performed for 20 unrelated patients affected by BOR syndrome, and six novel mutations were identified. Among these mutations, two are missense mutations, highlighting amino acid residues essential for the function of the EYA1 protein, and one mutation comprises a de novo Alu insertion into an exon. This insertion presumably occurs by retrotransposition, and the mobile Alu element has a poly(A) tail that is unstable throughout generations. To date, 14 mutations have been detected in BOR patients, all of which are different. However, all the mutations are located within or in the immediate vicinity of the eyaHR; the significance of this clustering is discussed.

Infusion of vincristine and doxorubicin with oral dexamethasone as first-line therapy for multiple myeloma

32 previously untreated patients with multiple myeloma received vincristine, doxorubicin ('Adriamycin'), and dexamethasone (VAD) as first-line therapy. The overall response rate was 84%, with 28% of all patients entering complete remission. Response was rapid, with near-maximum response occurring after two courses of treatment and rapid improvement in bone-marrow function. Median response duration was 18 months and this seemed to be unaffected by initial prognostic criteria or by degree of remission achieved. The projected median survival was 44 months, with 75% of all patients and 83% of responders being alive at 2 years. Side-effects due to steroids were common, but there was only 1 treatment-related death. The high response rate and lack of toxicity offer an advantage over other forms of initial treatment, although other strategies will be necessary to prolong the duration of response.

Intraoperative aneurysmal rupture: incidence, outcome, and suggestions for surgical management

Intraoperative rupture of an intracranial arterial aneurysm can dramatically interrupt a deliberate microsurgical procedure and jeopardize the patient's chances for a favorable outcome. Intraoperative rupture occurred in 58 of 307 (19%) consecutive aneurysm procedures done at The University of Texas Health Science Center. Rupture occurred during three specific periods: early or predissection in 7%, dissection in 48%, and clip application in 45%. Outcome after rupture during the predissection interval was poor, with only 1 of 4 patients surviving. Aneurysmal rupture during dissection could be attributed to blunt dissection techniques in 75% of the cases and to sharp subarachnoid dissection in 25%. The outcome was favorable in only 50% of the patients sustaining blunt dissection errors, whereas all patients sustaining intraoperative rupture during sharp dissection recovered well. Rupture during clip application was attributed to incomplete dissection in 65%, poor clip application in 31%, and a mechanical clip failure in 1 case. Eighty-eight per cent of the patients who underwent uneventful operative procedures had favorable outcomes, whereas only 62% of the patients suffering intraoperative rupture recovered well. The use of sharp microsurgical techniques with a systematic contingency plan for dealing with sudden hemorrhage and the judicious use of temporary clips should minimize the adverse effect of intraoperative rupture on overall management morbidity and mortality.

Surgery for paraclinoidal carotid artery aneurysms

Aneurysms arising from the proximal carotid artery between the roof of the cavernous sinus and the origin of the posterior communicating artery pose conceptual and technical surgical problems with regard to acquisition of proximal control and safe intracranial exposure. Over the past 3 1/2 years, 89 patients with paraclinoidal aneurysms have been treated at the University of Texas Southwestern Medical Center. Thirty-nine (44%) of these patients presented with subarachnoid hemorrhage. A total of 149 aneurysms and six arteriovenous malformations have been identified in this patient group such that 38 (43%) of the patients suffered multiple vascular anomalies. Temporary artery occlusion has been employed during operation in 48 cases (54%), permanent carotid artery occlusion in four (4%), and hypothermic circulatory arrest in two (2%). Twenty-two patients harbored giant aneurysms, seven of which had ruptured. Outcome was considered good in 77 patients (86.5%), fair in eight (9%), and poor in three (3%); one patient died. This concentrated experience permitted a practical anatomical grouping of aneurysms into three types: carotid-ophthalmic artery aneurysms with a superior or superomedial projection (44 cases); superior hypophyseal aneurysms with a medial or inferomedial projection (26 cases); and proximal posterior carotid artery wall aneurysms projecting posteriorly or posterolaterally (19 cases). Despite the fact that paraclinoidal aneurysms often disobey the traditional teachings of aneurysm development, having no vessel of origin or clear hemodynamic cause, this practical grouping has allowed individualized and focused operative approaches unique to each aneurysm projection with good visual function and outcome in most patients.

Intracranial arteriovenous malformations associated with aneurysms

The presence of intracranial aneurysm in association with arteriovenous malformation has been well documented. Aneurysms have been described in typical proximal sites along the feeding system to the arteriovenous malformation, in abnormal distal locations along feeding vessels, and in sites remote and apparently hemodynamically unrelated to the arteriovenous malformation. Little attention has been focused on the most appropriate medical and surgical care of patients harboring these lesions. Since 1977, 22 patients with this combination of lesions have been evaluated at our institution. Nine patients (41%) presented after intracranial hemorrhage. The remaining 13 patients were investigated because of seizures in 5 patients (23%), headaches in 4 patients (18%), and progressive ischemia in 4 patients (18%). Among the patients suffering intracranial hemorrhage, 78% had bled from an aneurysm, with 22% having hemorrhaged from their arteriovenous malformation. All 7 of the patients who suffered aneurysmal hemorrhage bled from atypical distal aneurysms on major feeding vessels. Our experience and that of others has led us to believe that the safest approach to patients with this combination of lesions is to treat the aneurysm before microsurgical resection of the associated arteriovenous malformation. Hemodynamic changes associated with the abrupt elimination of an arteriovenous malformation may place associated aneurysms at immediate risk.

Retrograde suction decompression of giant paraclinoidal aneurysms. Technical note

Giant paraclinoidal carotid artery aneurysms frequently require temporary interruption of local circulation to facilitate safe occlusion. Due to brisk retrograde flow through the ophthalmic artery and cavernous branches, simple trapping of the aneurysm by cervical internal carotid artery clamping and intracranial distal clipping may not adequately soften the lesion. The authors describe a retrograde suction method of aspiration of this collateral supply which they have used in over 40 cases. After temporary trapping, a No. 18 angiocatheter is inserted into the cervical internal carotid artery. This catheter is then connected to a wall suction point allowing rapid aneurysm deflation. This technique, accomplished by the surgical assistant, permits the surgeon the freedom to use both hands in dealing quickly with the aneurysm.

Extracorporeal photopheresis (ECP) in the treatment of chronic graft-versus-host disease (GVHD)

The aim of our study was to assess the efficacy of extracorporeal photopheresis (ECP) in chronic graft-versus-host disease (GVHD). Eleven patients with chronic cutaneous GVHD were studied. Four had mucosal involvement and five had pulmonary involvement. All had failed to improve on first- and second-line therapy. Three patients received ECP alone; the remainder continued to receive steroids and/or immunosuppressive therapy. Patients received ECP twice monthly for 4 months and then once monthly for 3 months. They were evaluated by serial skin scores, mucosal and skin photography, pulmonary function tests, biochemical and haematological parameters. Nine patients showed objective evidence of cutaneous improvement with a mean reduction in skin score of 48% overall. In the 10th patient, skin scores and oral involvement improved on twice monthly ECP but deteriorated when reduced to once monthly. The final patient died from renal failure secondary to cyclosporin toxicity. Two out of five patients with lung involvement showed a mild improvement in pulmonary function tests. Liver function tests were abnormal in five patients; they improved in one and deteriorated in three. All patients receiving concomitant immunosuppressive/steroid therapy were able to reduce drug dosages by trial completion. Our results indicate that ECP can benefit patients with cutaneous and mucosal chronic GVHD who have failed on first- and second-line therapies. The effect on the systemic manifestations of GVHD is less consistent.

Cerebrovascular hemodynamics in arteriovenous malformation complicated by normal perfusion pressure breakthrough

Catastrophic hyperemic states are known complications after the treatment of certain types of intracranial arteriovenous malformations (AVMs). A case is presented in which a large AVM was preoperatively embolized and later resected. There was clear intra- and postoperative evidence of edema and hemorrhage, which resulted in a fatal outcome. Regional cerebral blood flow (rCBF) data from this patient obtained with single photon emission computed tomography (SPECT) both before and after embolization were compared with data from four patients with similar size supratentorial AVMs treated and studied in a similar protocol who did not develop perfusion breakthrough. Pretreatment hemispheric rCBF was significantly reduced in this patient's ipsilateral hemisphere (50 ml/100 g/min) compared to the control group mean (83 +/- 9.5 ml/100 g/min). A similar relative depression was found in the contralateral hemisphere. After therapeutic embolization, the ipsilateral rCBF increased by 33 ml/100 g/min and the contralateral hemispheric rCBF increased by 30 ml/100 g/min; this embolization-induced increase in rCBF was significantly higher than in the control group. Acetazolamide, known to increase rCBF in normal tissue by 35 +/- 3%, resulted in a 56% augmentation of ipsilateral hemispheric flow before embolization in the reported patient vs. a 22 +/- 10% increase for the control group. Postembolization, this hyperresponsiveness to acetazolamide remained unchanged. It is possible that these hemodynamic derangements may indicate a dissociation between the vasoconstrictive and vasodilatory reactivity in chronically hypoperfused territories adjacent to AVMs such that pharmacological or metabolic stimuli may induce further vasodilation, but sudden redistribution of large volumes of flow will not promote protective vasoconstriction.

Arteriovenous malformations of the posterior fossa. Clinical presentation, diagnostic evaluation, and surgical treatment

Infratentorial arteriovenous malformations (AVM's) represent only 5% to 7% of all AVM's in major series. Since 1977, 32 patients with intracranial intradural malformations of the brain stem or cerebellum have been evaluated at the University of Texas Health Science Center, 30 of whom underwent surgical treatment. Twenty-three patients presented with intracranial hemorrhage, which was recurrent in 11 cases, and nine patients were evaluated for progressive brain-stem or cerebellar deficits. A history of progressive deficits was unusual in the group that presented with hemorrhage, and a prior or subsequent hemorrhage was rare in the patients initially evaluated for progressive deficits. Seventeen of these AVM's were located in the vermis, seven within the cerebellar hemisphere, two in the tonsil, two in the cerebellopontine angle, and four within the brain stem. Operative intervention was directed at primary resection in 15 cases, staged resection in seven, embolization and resection in five, and evacuation of hematoma in three. Operative mortality in this surgical series was 7%, with significant morbidity in 13%. Use of modern microsurgical techniques in removal of posterior fossa AVM's may offer results better than the natural history of the disease process, especially in patients who present with hemorrhage.

Mental calculation in a prodigy is sustained by right prefrontal and medial temporal areas

Calculating prodigies are individuals who are exceptional at quickly and accurately solving complex mental calculations. With positron emission tomography (PET), we investigated the neural bases of the cognitive abilities of an expert calculator and a group of non-experts, contrasting complex mental calculation to memory retrieval of arithmetic facts. We demonstrated that calculation expertise was not due to increased activity of processes that exist in non-experts; rather, the expert and the non-experts used different brain areas for calculation. We found that the expert could switch between short-term effort-requiring storage strategies and highly efficient episodic memory encoding and retrieval, a process that was sustained by right prefrontal and medial temporal areas.