The aqueduct of Sylvius: a sonographic landmark for neural tube defects in the first trimester.

OBJECTIVES: To describe a new first-trimester sonographic landmark, posterior displacement of the midbrain and aqueduct of Sylvius, which may be useful in early screening for neural tube defects. METHODS: This was a prospective study of 457 normal fetuses at 11 + 0 to 13 + 6 weeks' gestation. We measured the distance from the posterior border of the aqueduct of Sylvius to the anterior border of the occiput (AOS-to-occiput distance) in the axial plane and created a reference range. In the nine fetuses with abnormal midbrain position identified in the first trimester and with neural tube defect subsequently confirmed, we analyzed ultrasound images to determine the position of the aqueduct of Sylvius. RESULTS: The lower limit of normal AOS-to-occiput distance (mean minus 2 SD) ranged from 1.7 mm at a crown-rump length (CRL) of 45 mm to 3.7 mm at a CRL of 84 mm. In the nine cases with abnormal position of the midbrain and confirmed neural tube defect, juxtaposition of the midbrain to the occiput was the clue to diagnosis of the spinal abnormality. In all nine cases, the AOS-to-occiput distance was below the established normal range. CONCLUSIONS: Examination of the midbrain in an axial plane may prove a reliable marker for the first-trimester diagnosis of neural tube defects. In contrast to recently reported subtle changes in the mid-sagittal view of the posterior cranial fossa, axial imaging of the midbrain reveals striking displacement of this structure, with virtual juxtaposition to the occiput, in fetuses with confirmed open spina bifida. This anatomical distortion of the midbrain can be quantified by measurement of the AOS-to-occiput distance.

Endoglycosidase f cleaves the oligosaccharides from the glucose transporter of the human erythrocyte.

The glucose transporter from human erythrocytes is a heterogeneously glycosylated protein that runs as a very broad band of average apparent Mr 55 000 upon sodium dodecyl sulfate polyacrylamide gel electrophoresis. When the purified preparation of transporter, solubilized in Triton X-100, was treated with endoglycosidase F, much of it ran as a sharp band of Mr 46 000 upon electrophoresis. Moreover, endoglycosidase F released 80% of the radioactivity in a preparation of the transporter labeled in its oligosaccharides with galactose oxidase and tritiated borohydride, and almost none of the remaining radioactivity was located in the Mr 46 000 band. These results suggest that endoglycosidase F can release virtually all of the carbohydrate linked to the transporter polypeptide. A quantitative analysis of the gels was complicated by partial aggregation of polypeptides that occurs due to prolonged incubation in Triton X-100, but at least 65% of the protein in the preparation of purified transporter is the 46 kDa polypeptide. The extracellular domain of the transporter is very resistant to proteolysis; no cleavage occurred upon treatment of intact erythrocytes with seven different proteases at high concentration.

Identification of the glucose transporter in rat skeletal muscle.

The glucose transporter in the plasma membrane of rat skeletal muscle has been identified by two approaches. In one, the transporter was detected as the polypeptide that was differentially labeled by photolysis with [3H]cytochalasin B in the presence of L- and D-glucose. [3H]Cytochalasin B is a high-affinity ligand for the transporter that is displaced by D-glucose. In the other, the transporter was detected by means of its reaction with rabbit antibodies against the purified glucose transporter from human erythrocytes. By both procedures, the transporter was found to be a polypeptide with a mobility corresponding to a molecular weight of 45,000-50,000 upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis.