Plasma homocysteine concentrations and the single nucleotide polymorphisms in the methionine synthase gene (MTR 2756A>G): Associations with the polycystic ovary syndrome An observational study

BACKGROUND: Elevated plasma homocysteine (Hcy) is a recognized risk factor for cardiovascular disease (CVD) and other defects. Biochemical and genetic studies have characterized molecular determinants contributing to alter Hcy metabolism. The vitamin B12 dependent enzyme methionine synthase (MTR) regulates de novo production of methionine from homocysteine. Defects in the activity of this enzyme may possibly predispose to higher plasma Hcy concentrations. STUDY DESIGN: We examined the associations between plasma Hcy concentrations and a single nucleotide polymorphism (SNP) in the MTR gene (MTR 2756A>G), and plasma folate concentrations, in 71 women (Caucasian and South Asian) attending a fertility clinic. We also determined the ethnic variations in the frequencies of the 3 genotypes of the MTR 2756 A>G gene. RESULTS: The frequency of the variant G allele was similar in the Caucasians and the South Asians (OR: 1.83; 95% CI: 0.79-4.23, p=0.2). The frequency was also similar in the PCOS and non-PCOS groups (OR: 0.88; 95% CI: 0.39-1.99). Plasma Hcy levels were significantly higher in women with PCOS compared with non-PCOS controls (p=0.05) and in Caucasian women with PCOS compared with Caucasian controls (p=0.04) in the presence of the MTR 2756 AA genotype (wild type). After adjusting for age, BMI, waist circumference and ethnicity, the significant predictors of plasma Hcy concentrations were plasma LDL, whole blood folate concentrations and a clinical diagnosis of PCOS. CONCLUSIONS: The important predictors of plasma Hcy concentration in women of reproductive age are whole blood folate concentrations, a background of PCOS and plasma LDL concentrations. The SNP 2756 A>G in the MTR gene does not appear to influence the plasma Hcy levels.     

Guidelines for using human event-related potentials to study cognition: recording standards and publication criteria

Event-related potentials (ERPs) recorded from the human scalp can provide important information about how the human brain normally processes information and about how this processing may go awry in neurological or psychiatric disorders. Scientists using or studying ERPs must strive to overcome the many technical problems that can occur in the recording and analysis of these potentials. The methods and the results of these ERP studies must be published in a way that allows other scientists to understand exactly what was done so that they can, if necessary, replicate the experiments. The data must then be analyzed and presented in a way that allows different studies to be compared readily. This paper presents guidelines for recording ERPs and criteria for publishing the results.     

Human auditory steady-state responses to amplitude-modulated tones: phase and latency measurements

Human auditory steady-state responses were recorded to four stimuli, with carrier frequencies (f(c)) of 750, 1500, 3000 and 6000 Hz, presented simultaneously at 60 dB SPL. Each carrier frequency was modulated by a specific modulation frequency (f(m)) of 80.6, 85.5, 90.3 or 95.2 Hz. By using four different recording conditions we obtained responses for all permutations of f(m) and f(c). The phase delays (P) of the responses were unwrapped and converted to latency (L) using the equation: L=P/(360xf(m)). The number of cycles of the stimulus that occurred prior to the recorded response was estimated by analyzing the effect of modulation frequency on the responses. These calculations provided latencies of 20.7, 17.7, 16.1 and 16.1 ms for carrier frequencies 750, 1500, 3000 and 6000 Hz. This latency difference of about 4.5 ms between low and high carrier frequencies remained constant over many different manipulations of the stimuli: faster modulation rates (150-190 Hz), binaural rather than monaural presentation, different intensities, stimuli presented alone or in conjunction with other stimuli, and modulation frequencies that were separated by as little as 0.24 Hz. This frequency-related delay is greater than that measured using transient evoked potentials, most likely because of differences in how transient and steady-state responses are generated and how their latencies are determined.     

Human auditory evoked potentials recorded using maximum length sequences.

A maximum length sequence (MLS) is a specially constructed pseudorandom binary sequence that can be used to control the presentation of sensory stimuli. The evoked potentials to such a sequence of stimuli can be analyzed to give the response to one stimulus in the sequence. This procedure allows auditory evoked potentials to be recorded at stimulus rates that would cause a confusing overlap of responses with regular averaging. The MLS technique can be used with auditory evoked potentials at all latencies although it is most effective for the brain-stem and middle-latency responses. By demonstrating different refractory periods for different parts of the response, the technique may help delineate the component structure of the evoked potential. As well, an MLS analysis can disentangle the auditory brain-stem response from overlapping middle-latency responses during evoked potential audiometry.     

Fetal growth achievement and elevated maternal serum alpha-fetoprotein

Maternal serum alpha-fetoprotein (AFP) was measured by radioimmunoassay in 7223 unselected patients between 16 and 20 weeks gestation. In 141 patients an elevated AFP level (greater than 2.5 multiples of the median for gestation) was found in the absence of a primary cause. When the birthweights of the 137 liveborn infants were corrected for maternal height and weight, sex and birth rank, 37 (27%) fell below the 10th centile of normal birthweight standards. No excess of premature deliveries was found, but there was a significant association with primiparity. Patients delivered of their second infant showed a significant decrement in mean birthweight when compared with their first-born infants and with a matched control group (normal maternal serum AFP levels). There was a highly significant association between elevated serum AFP and subsequent placental abruption.     

A technique for measuring eruption rates in rats of maxillary incisors under intrusive forces.

The heads of six rats were immobilised and the position of a maxillary incisor was monitored by a displacement transducer. The weight of the central spindle of the transducer was balanced by weights applied to the far end of a pivoted bar. Intrusive forces were applied by placing weights on the near end of this bar. With opposing forces of less than 0.3 mN, the eruption rates for the six rats were between 10 and 64 μm/h, with a mean value of 34 (SD ± 16) μm/h, little more than the unimpeded eruption rate of the rat maxillary incisor.The incisor tooth pulsated in its socket.