Identification and functional characterization of a novel MTFMT mutation associated with selective vulnerability of the visual pathway and a mild neurological phenotype.

Mitochondrial protein synthesis is initiated by formylated tRNA-methionine, which requires the activity of MTFMT, a methionyl-tRNA formyltransferase. Mutations in MTFMT have been associated with Leigh syndrome, early-onset mitochondrial leukoencephalopathy, microcephaly, ataxia, and cardiomyopathy. We identified compound heterozygous MTFMT mutations in a patient with a mild neurological phenotype and late-onset progressive visual impairment. MRI studies documented a progressive and selective involvement of the retrochiasmatic visual pathway. MTFMT was undetectable by immunoblot analysis of patient fibroblasts, resulting in specific defects in mitochondrial protein synthesis and assembly of the oxidative phosphorylation complexes. This report expands the clinical and MRI phenotypes associated with MTFMT mutations, illustrating the complexity of genotype-phenotype relationships in mitochondrial translation disorders.

The associations among hippocampal volume, cortisol reactivity, and memory performance in healthy young men.

In aged and pathological populations, reduced hippocampal volume is frequently described in association with impairment of hippocampus-dependent cognitive processes and chronically elevated cortisol levels. Recent studies in young healthy subjects show a negative association between hippocampal volume and memory. The aim of the present study was to investigate the associations among hippocampal volume, cortisol levels and memory performance in a group of healthy young men. Hippocampal volume was determined by manual segmentation of high-resolution 3D Magnetic Resonance Images from 13 subjects. Stress-induced cortisol levels in response to the "Trier Social Stress Test" (TSST) as well as the cortisol response to awakening (CRA) over four weeks were assessed. Declarative memory performance was tested before and after exposure to the TSST. The results show that larger hippocampal volume was associated with a significantly stronger cortisol increase in response to the TSST and a significantly greater CRA. Moreover, larger hippocampal volume was associated with significantly lower memory performance before the TSST. Our results challenge the direction of the frequently observed relationships among hippocampal volume, cortisol reactivity and memory performance and question the relevance of findings in clinical and aged subjects for young healthy populations.

A new anatomical landmark for reliable identification of human area V5/MT: a quantitative analysis of sulcal patterning.

The location of human area V5 (or MT) has been correlated with the intersection of the ascending limb of the inferior temporal sulcus (ALITS) and the lateral occipital sulcus (LO). This study was undertaken to attempt a replication and quantification of these observations using functional magnetic resonance imaging. V5 was significantly activated in 19 hemispheres with alternating, low contrast, random checkerboard patterns. We confirmed the stereotaxic location of V5 and were able to describe a fairly consistent sulcal pattern in the parieto-temporo-occipital cortex. V5 was usually (95%) buried within a sulcus, most commonly within the inferior temporal sulcus (ITS) (11%), the ascending limb of the ITS (ALITS) (53%) and the posterior continuation of the ITS (26%). The average distance from V5 of two identified anatomical landmarks of V5, the junctions of the LO and the ALITS, and the ITS and ALITS, were both 1 cm. However, the LO-ALITS junction often had to be determined by interpolation (47%), and was not always present even with interpolation (21%). In contrast, the ITS-ALITS junction was always present and V5 was usually (90%) located in a sulcus intersecting with this junction, making it a more reliable landmark for localizing V5 with respect to gross morphological features on individual cortical surfaces.