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Biomedical subjects

A H Lang

Publications and source records attributed to A H Lang.

At least 19 recordsLinked to original sources
PubMed1999

Global sequence diversity of BRCA2: analysis of 71 breast cancer families and 95 control individuals of worldwide populations.

The aim of this study was to evaluate the prevalence of simple sequence variation in the BRCA2 gene. To this end, 71 breast and breast-ovarian cancer (HBC/HBOC) families along with 95 control individuals from a wide range of ethnicities were analyzed by means of denaturing high-performance liquid chromatography (DHPLC) and direct sequence analysis. In the coding (10 257 bp) and non-coding (2799 bp) sequences of BRCA2, 82 sequence variants were identified. Three different, apparently disease-associated BRCA2 mutations were found in six HBC/HBOC families (8%): two splice site mutations in introns 5 and 21, and one frameshift mutation in exon 11. In the coding region, 53 simple sequence variants were found: 35 missense mutations, one 2 bp deletion (CT) resulting in a stop at codon 3364, one nonsense mutation with a stop at codon 3326, one deletion of a complete codon (AAA) resulting in the loss of leucine, and 15 silent mutations. In the non-coding region, 26 polymorphisms were detected. Of the 79 sequence variants that were not obviously disease-associated, eight were detected only in HBC/HBOC families. The remaining 71 variants were identified in both HBC/HBOC families and control individuals. Sixty three sequence variants (80%) were specific for a continent. Forty two percent (33 out of 79) of the sequence variants were detected exclusively in Africa, though only 13% of the 332 chromosomes screened were of African origin. Our data indicate that, in BRCA2, simple sequence variation is frequent [in the coding region 1 in 194 bp (straight theta = 2.2 x 10(-4)), and in the non-coding region 1 in 108 bp (straight theta = 4.4 x 10(-4)), respectively].

Africa↗
PubMed1998

BRCA1-related breast cancer in Austrian breast and ovarian cancer families: specific BRCA1 mutations and pathological characteristics.

We identified 17 BRCA1 mutations in 86 Austrian breast and ovarian cancer families (20%) that were screened for mutations by denaturing high-performance liquid chromatography (DHPLC) and the protein truncation test (PTT). Eleven distinct mutations were detected, 4 of them (962del4, 2795del4, 3135del4 and L3376stop) not previously reported in families of non-Austrian origin. In addition, 6 rare missense mutations (allele frequency < 1%) with unknown biological effects were identified. Four mutations occurred more than once in the Austrian population: 2795del4 (3 times), Cys61Gly (3 times) 5382insC (2 times) and Q1806stop (2 times). Haplotype analysis of the 4 recurrent mutations suggested a common ancestor for each of these. Thirty-four breast cancer cases from 17 families with BRCA1 mutations were further analyzed. We observed a low median age of onset (39.5 years). Sixty-eight percent of all BRCA1 breast cancer cases had negative axillary lymph nodes. This group showed a significant prevalence of a negative estrogen and progesterone receptor status and stage I tumors compared with an age-related, node-negative control group. The prevalence of grade III tumors was marginally significant. Survival analysis either with a control group matched for age (within 5 years), grade, histologic subtype and estrogen receptor status, or with an age-related, node-negative comparison group, showed no statistical difference.

Adult↗
PubMed1998

Event-related desynchronization and synchronization during an auditory lexical matching task.

OBJECTIVES: Event-related desynchronization (ERD) and synchronization (ERS) of the 8-10 and 10-12 Hz frequency bands of the background EEG were studied in 10 subjects performing an auditory lexical matching task. METHODS: The stimuli were words and pseudowords presented sequentially in pairs. The subject was prompted to answer whether the two stimuli shared the same lexical status (words or pseudowords). RESULTS: Regardless of lexicality, the presentation of the first stimulus elicited a significant late frontal ERD in both alpha frequency bands. When preceded by a pseudoword, the presentation of the second stimulus elicited a significant ERS at 200-400 ms and a significant, long-lasting and topographically-widespread ERD at 600-2200 ms in both frequency bands. When preceded by a word, the second stimulus did not elicit ERS in the initial time window, but a late ERD which was similar to the one observed in the previous condition. The complexity of ERD/ERS changes in the present task was revealed by significant interactions that time had with frequency band, stimulus type, stimulus order and lexicality of the preceding stimulus. CONCLUSIONS: The results suggest that ERD/ERS does not reflect primary auditory stimulus processing. Rather, the ERD/ERS observed in this experiment most probably reflected task difficulty and differences between lexical-semantic and phonological memory functions.

Adult↗
PubMed1997

Relative alpha desynchronization and synchronization during speech perception.

Brain processes elicited by speech were studied in 10 right-handed subjects by means of examining the desynchronization and synchronization of the 8-10 Hz and 10-12 Hz EEG alpha frequency bands. The subjects listened to an auditorily presented 5 min text passage. The text was presented both forward and backward. Listening to the text forward elicited alpha desynchronization in both of the frequency bands studied, whereas listening to the same text presented backward elicited synchronization in the 10-12 Hz frequency band only. Listening to the text forward elicited greater desynchronization than listening to the text backward. In the 10-12 Hz frequency band, listening to the text forward elicited desynchronization whereas listening to the same text backward elicited synchronization. This dissociation was not observed in the 8-10 Hz frequency band. The results suggest that the lower and upper alpha bands differ such that the 10-12 Hz frequency band exhibits reactivity to the presence of linguistic content while the 8-10 Hz band shows an unspecific response.

Acoustic Stimulation↗
PubMed1997

Neurophysiological findings in the northern epilepsy syndrome.

We describe the neurophysiological findings in the northern epilepsy syndrome (NES), an autosomal recessively inherited childhood onset epilepsy with associated mental deterioration. Sixty-five EEGs of 18 patients (10 females and 8 males) from the age of 5 years to 52 years were analyzed. EEG showed relatively slight changes at the outbreak of epilepsy at the mean age of 6.6 years (range 5-10 years). Slowing of the background activity to 6-7 Hz theta activity, abundant diffuse or intermittent theta and delta activity and disappearance of sleep-specific activity characterized the EEGs at puberty. The amount of diffuse delta and theta activity diminished in adulthood. Epileptiform findings were scanty. Spikes and sharp waves occurred in 43% of the recordings with varying localization, form and extent. Intermittent 2-4 Hz sharp and slow wave rhythm was seen in 32% of the recordings. Of the three ictal recordings, one showed a primarily generalized discharge pattern, while two were clearly asymmetric. Clonazepam was the most effective antiepileptic drug, and it also normalized the EEG when started in childhood or at the onset of puberty. Visual evoked potentials were abnormal in 44% and brainstem auditory evoked potentials in 35%. The neurophysiological findings suggest an extensive, probably multifocal degenerative brain process, which reaches its peak at puberty. Although the abnormal features of EEG often decreased in adulthood, the clinical course of NES showed slow progression throughout the lifetime.

Adolescent↗
PubMed1997

Perceptual magnet effect in the light of behavioral and psychophysiological data.

Finnish speaking adults categorized synthetic vowels, varying in the frequency of the second formant (F2), as either /y/ or /i/. Two subject groups emerged: "good" and "poor" categorizers. In a /i/ rating experiment, only the good categorizers could consistently label their best /i/ (the prototype, P), being low in the F2 continuum. Poor categorizers rated /i/'s with high F2 values as Ps. In a same/different (AX) discrimination experiment, using the individual Ps and nonprototypes (NPs), it was more difficult for good categorizers to detect small F2 deviations from the P than from an NP (the "perceptual magnet effect"). For poor categorizers, the opposite effect was found. The same stimuli were used to record the mismatch negativity (MMN), an ERP component reflecting preattentive detection of deviations from a standard sound. For the good categorizers the MMNs were lower for Ps than for NPs; for the poor categorizers the MMNs for Ps and NPs did not differ significantly. The results show that individual listeners behaved differently in categorization and goodness rating but in the same way in attentive (AX) discrimination, being the poorest at about the same F2 location. The perceptual magnet effect was indicated in the good categorizers both by behavioral and psychophysiological (MMN) discrimination data.

Adult↗
PubMed1996

Event-related EEG desynchronization and synchronization during an auditory memory task.

Event-related desynchronization (ERD) and synchronization (ERS) of the lower (8-10 Hz) and upper (10-12 Hz) alpha bands of background EEG were studied in 10 subjects during an auditory memory scanning paradigm. Each experimental trial started with the presentation of a visual warning signal, after which an auditory 4-vowel memory set was presented for memorization. Thereafter the probe, a fifth vowel, was presented and identified by the subject as belonging or not belonging to the memorized set. In 50% of the cases, the probe was among the previously presented memory set. The presentation of the memory set elicited a significant ERS in the both alpha frequency bands. In contrast, the presentation of the probe elicited a significant bilateral ERD in both alpha frequency bands studied. The results suggest that the ERD phenomenon is closely associated with higher cortical processes such as memory functions rather than with auditory stimulus processing per se. Event-related desynchronization provides a potentially valuable tool for studying cortical activity during cognitive processing in the auditory stimulus modality.

Adult↗
PubMed1995

Practical issues in the clinical application of mismatch negativity.

The mismatch negativity (MMN) recordings provide an objective measure of the preattentive, automatic auditory discrimination function. This article deals with issues central to the recording of the MMN and the interpretation of the results for clinical and electrodiagnostic purposes. The methods of acquiring as pure an MMN response as possible, i.e., one not contaminated by auditory cortical responses reflecting other functions, are discussed first. Second, other technical questions associated with the recording are reported on, e.g., what MMN parameters should be recorded and how, what is the smallest recordable MMN response, and what is the repeatability of the MMN recordings. Then, the effect of various physiological factors on the MMN (age, alertness, gender, topographic distribution of the MMN) is considered. The correlation between auditory discrimination performance and the MMN amplitude, observed in normal population, is dealt with. Finally, there is a short concluding overview on clinical findings of MMN recordings and discussion on their electrodiagnostic applications.

Amplifiers, Electronic↗
PubMed1995

Effect of contralateral white noise masking on the mismatch negativity.

Mismatch negativity (MMN), an auditive event-related potential (ERP) component, evoked by deviant stimuli in a homogeneous stream of standard stimuli was studied in a unilateral stimulation and contralateral white noise masking condition. Eleven subjects (Ss) with normal hearing (aged 20-35 years) were examined using sine tone stimuli (70 dB HL, interstimulus interval 300 ms, duration 40 ms with 5 ms rise and fall times). Three blocks of standard (std)/deviant (dev) series of stimuli were used: std 500/dev 600 Hz, std 2000/dev 1900 Hz, and std 2000/dev 1600 Hz. The first block was repeated for another group of 11 Ss with normal hearing (aged 17-27 years). The MMN was analysed from the difference curves recorded at Fz, Cz and Pz. The stimuli were delivered unilaterally, either with or without 50 dB effective masking level white noise to the contralateral ear. The MMN amplitude attenuated significantly when contralateral masking was used. In addition, there was interaction between noise masking and the stimulated ear. The MMN latencies were not affected by white noise masking.

Adult↗
PubMed1994

Automatic discrimination of phonetically relevant and irrelevant vowel parameters as reflected by mismatch negativity.

An auditory event-related brain potential called mismatch negativity (MMN) was measured to study the perception of vowel pitch and formant frequency. In the MMN paradigm, deviant vowels differed from the standards either in F0 or F2 with equal relative steps. Pure tones of corresponding frequencies were used as control stimuli. The results indicate that the changes in F0 or F2 of vowels significantly affected the MMN amplitudes. The only variable significantly affecting the MMN latencies was sex which, however, did not have any effect on the amplitudes of the MMN. As expected, the MMN amplitudes increased with an increase in the acoustical difference between the standards and the deviants in all cases. On the average, the amplitudes were lower for the vowels than for the pure tones of equal loudness. However, in vowels, minor frequency changes in F0 produced higher MMN amplitudes than similar relative changes in F2. It was also noted that even the smallest and phonetically irrelevant change in F2 was detected by the MMN process. In overall, the results demonstrate that the MMN can be measured separately for F0 and F2 of vowels, although the MMN responses show large interindividual differences.

Adult↗
PubMed1990

Transient asymmetries of steady-state visual evoked potentials in classic migraine.

Unilateral abnormalities in the regional cerebral blood flow (rCBF) and visual evoked potentials (VEPs) during the visual aura of classic migraine have been reported. On the other hand, there are only few observations suggesting unilateral abnormality of neural function during the headache-free period. An experiment is described in which the symmetries of steady state VEPs (SVEPs) are compared in healthy subjects and classic migraineurs in the headache-free interval. In the patients an increased number of strong short-lasting interhemispheric asymmetries was found. In the serial recordings performed, pathologic recordings were obtained intermittently, usually with complete normalisation in the following session. The incidence of abnormalities was relatively independent of the interval between the recording and attack, except for the next few hours. The findings may be related to instability of occipital cortical function in classic migraine.

Adult↗
PubMed1989

Difference of steady-state visual evoked potentials in classic and common migraine.

The present study was designed to find evidence for the neural hypothesis of migraine and to evaluate possible interictal differences in the two varieties of migraine by electrophysiological means. Steady-state visual evoked potentials (SVEPs) in response to sinusoidally modulated light were measured in 20 patients with classic migraine and compared with those of 30 common migraineurs and 49 reference subjects. SVEPs to stimuli at 10-24 Hz were recorded occipitally from a pair of midline electrodes and, in classic migraineurs and controls, additionally from left and right occipital areas. The response was processed by the Fast Fourier Transform and automatically analysed. The fundamental component of the midline response to medium frequency stimuli (16-22 Hz) appeared normal in patients with classic migraine, contrary to an augmented response in common migraineurs (ANOVA between groups, P = 0.006). In classic migraine the 2nd harmonic component was attenuated (P less than 0.01 at 18-20 Hz) and the amount of strong interhemispheric f1 asymmetries was increased in about half of the patients. The groups also diverged significantly in the SVEP dynamics during stimulation. The results support the hypothesis of a primary neural disorder in both types of migraine. Different sites and mechanisms of brain dysfunction in classic and common migraine are suggested. Hypothetical neuroanatomical correlates for the abnormalities are presented.

Adult↗
PubMed1985

[Pump-guided continuous subcutaneous opiate infusion for the treatment of the most severe pain].

The continuous subcutaneous infusion of opiate, a new approach to the alleviation of severe chronic pain, has been carried out using a pump system normally employed for the infusion of insulin. Relapses of pain can be controlled with bolus doses. This mode of application was compared with conventional therapy in 11 patients. All patients were free of pain during the continuous infusion, but none showed a satisfactory response during conventional treatment. The improved response under continuous opiate infusion was attained with much lower doses and thus with fewer side effects. The procedure is therefore highly effective and well tolerated.

Adult↗
PubMed1984

Steady-state visual evoked potentials during migraine prophylaxis by propranolol and femoxetine.

The amplitude of visual evoked potentials (VEPs) for flickering light has been reported to be increased in migraine. In the present study, we have examined whether the VEPs are attenuated when the clinical state of the patient improves during a double-blind experiment with propranolol and femoxetine. VEPs for sinusoidally-modulated light were measured by spectral analysis, and an index depicting the visual reaction type was calculated. The group mean VEP index closely followed the group mean attack frequency, but individual variance was considerable. The changes were most evident in VEPs elicited by stimuli of about 20 Hz. During the treatments, the VEP and headache were also significantly correlated among subjects. The results suggest a close relationship between the enlarged VEPs and the headache mechanisms.

Adult↗
PubMed1983

Acute effects of intravenously given alcohol on saccadic eye movements and subjective evaluations of intoxication.

Effects of intravenously given alcohol on eye movements were analysed in ten voluntary subjects. Each subject served as his/her own control. Good correlations were found between the changes in saccade variables and subjective evaluations of alertness, eye movement control and intoxication. Interindividually, the subjective evaluation of drunkenness correlates with the alcohol effect on saccade variables better than do the other subjective variables or blood or breath alcohol concentrations. A steady decrease of mean and maximum velocity and a steady increase in the duration of saccades was observed during the alcohol infusion. The latency of saccades also increased. There was, however, a slight decrease of latency due to alcohol 15 min after the start of infusion, suggesting a biphasic effect of alcohol on saccade latency.

Alcoholic Intoxication↗
PubMed1983

Vestibular neuronitis; a neurological and neurophysiological evaluation.

Neurological and neurophysiological findings were retrospectively reviewed in a group of 50 patients with vestibular neuronitis (VN). The onsets of VN were found to be clustered in the period from August to January. A preceding infection was reported by 36% of the patients. Neurological examinations did not reveal any other relevant signs than a spontaneous nystagmus during the acute phase. The results of routine laboratory tests and cerebrospinal fluid tests were within normal limits. EEG was recorded in 37 patients; 15 patients had a definitely abnormal EEG, with a slowing of the dominant occipital rhythm or more generalized diffuse slowing in 12 cases. 5 patients, 3 of them without slowing of the background activity, had a distinct focal disturbance of intermittent slow activity in the temporal region. In control recordings, an improvement was seen in the slowing of the background activity but not in the focal disturbances. Brainstem auditory evoked responses (BSER) were recorded in 12 patients, 5 of whom had abnormal responses. The seasonal clustering of VN onsets and the association of VN with overt infections further suggest its infectious pathogenesis. The observed EEG and BSER disturbances suggest a subclinical brainstem involvement in some cases of VN.

Adolescent↗