Autosomal recessive renal tubular dysgenesis (RTD) is a severe disorder of renal tubular development characterized by early onset and persistent fetal anuria leading to oligohydramnios and the Potter sequence, associated with skull ossification defects. Early death occurs in most cases from anuria, pulmonary hypoplasia, and refractory arterial hypotension. The disease is linked to mutations in the genes encoding several components of the renin-angiotensin system (RAS): AGT (angiotensinogen), REN (renin), ACE (angiotensin-converting enzyme), and AGTR1 (angiotensin II receptor type 1). Here, we review the series of 54 distinct mutations identified in 48 unrelated families. Most of them are novel and ACE mutations are the most frequent, observed in two-thirds of families (64.6%). The severity of the clinical course was similar whatever the mutated gene, which underlines the importance of a functional RAS in the maintenance of blood pressure and renal blood flow during the life of a human fetus. Renal hypoperfusion, whether genetic or secondary to a variety of diseases, precludes the normal development/ differentiation of proximal tubules. The identification of the disease on the basis of precise clinical and histological analyses and the characterization of the genetic defects allow genetic counseling and early prenatal diagnosis.

The plastic deformation of sapphire (a-AI,O,) has been studied under hydrostatic confining pressure at temperatures below the ambient pressure brittle-to-ductile transition temperature. Samples oriented for prism plane slip (Type I samples) were deformed via dislocation slip at temperatures as low as 200°C. Samples oriented for basal slip (Type I1 samples) could be plastically deformed at temperatures as low as 400°C but showed more complicated deformation behavior, inasmuch as the sample orientation also allowed for the activation of basal twinning and two of the three rhombohedral twin systems. The temperature dependence of the critical resolved shear stress ( I~~J ,for basal slip was significantly greater than that for prism plane slip (Bbasal > BpriPmplane), causing the latter system to be the easy slip system below -600°C (basal slip is the easy slip system at elevated temperatures). Type I1 samples deformed primarily by basal twinning in preference to both rhombohedral twinning and basal slip. The different temperature dependence of T , , for basal and prism plane slip is attributed to details of the dislocation core structure; prism plane dislocations, having a large Burgers vector ( lbppl = 0.822 nm), can dissociate into three collinear partials ([bpi = 0.274 nm) separated by relatively low-energy stacking faults, whereas the comparable dissociation of basal dislocations (lbsl = 0.476 nm) produces two noncollinear partials separated by a relatively high energy stacking fault. Thus, dissociation of basal dislocations is most likely restricted to the dislocation core, which is manifested in a higher Peierls stress at low temperatures for basal slip compared to prism plane slip.

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Dislocations have been introduced in GaAs doped with indium, by plastic deformation between 773 K and 1 373 K. Transmission electron microscope observations have shown that indium increases the width of dissociation. This can explain the reduction of as-grown dislocations in In doped GaAs