Recommendations on scuba diving in Birt-Hogg-Dubé syndrome

INTRODUCTION

Although very uncommon, severe injury and death can occur during scuba diving. One of the main causes of scuba diving fatalities is pulmonary barotrauma due to significant changes in ambient pressure. Pathology of the lung parenchyma, such as cystic lesions, might increase the risk of pulmonary barotrauma.

AREAS COVERED

Birt-Hogg-Dubé syndrome (BHD), caused by pathogenic variants in the FLCN gene, is characterized by skin fibrofolliculomas, an increased risk of renal cell carcinoma, multiple lung cysts and spontaneous pneumothorax. Given the pulmonary involvement, in some countries patients with BHD are generally recommended to avoid scuba diving, although evidence-based guidelines are lacking. We aim to provide recommendations on scuba diving for patients with BHD, based on a survey of literature on pulmonary cysts and pulmonary barotrauma in scuba diving.

EXPERT OPINION

In our opinion, although the absolute risks are likely to be low, caution is warranted. Given the relative paucity of literature and the potential fatal outcome, patients with BHD with a strong desire for scuba diving should be informed of the potential risks in a personal assessment. If available a diving physician should be consulted, and a low radiation dose chest computed tomography (CT)-scan to assess pulmonary lesions could be considered.

Modest phenotypic improvements in ASA-deficient mice with only one UDP-galactose:ceramide-galactosyltransferase gene

Background

Arylsulfatase A (ASA)-deficient mice are a model for the lysosomal storage disorder metachromatic leukodystrophy. This lipidosis is characterised by the lysosomal accumulation of the sphingolipid sulfatide. Storage of this lipid is associated with progressive demyelination. We have mated ASA-deficient mice with mice heterozygous for a non-functional allele of UDP-galactose:ceramide-galactosyltransferase (CGT). This deficiency is known to lead to a decreased synthesis of galactosylceramide and sulfatide, which should reduce sulfatide storage and improve pathology in ASA-deficient mice.

Results

ASA-/- CGT+/- mice, however, showed no detectable decrease in sulfatide storage. Neuronal degeneration of cells in the spiral ganglion of the inner ear, however, was decreased. Behavioural tests showed small but clear improvements of the phenotype in ASA-/- CGT+/- mice.

Conclusion

Thus the reduction of galactosylceramide and sulfatide biosynthesis by genetic means overall causes modest improvements of pathology.

Specific downregulation and mistargeting of the lipid raft-associated protein MAL in a glycolipid storage disorder

Metachromatic leukodystrophy (MLD) is a lysosomal lipid storage disease caused by arylsulfatase A deficiency. In MLD patients the sphingolipid sulfatide increasingly accumulates leading to progressive demyelination. We have analysed arylsulfatase A-deficient mice, a MLD mouse model, and we show that accumulation of sulfatide is not restricted to the lysosomal compartment but also occurs in myelin itself. Although, this sulfatide storage did not affect the overall composition of most myelin proteins, it specifically caused a severe reduction of MAL. This demonstrates a regulatory link between sulfatide accumulation and MAL expression and indicates the existence of regulatory mechanisms between lipid and myelin protein synthesis in oligodendrocytes. In addition, in cultured renal epithelial cells, sulfatide accumulation diverts MAL to the late endosomal/lysosomal compartment and thus also affects the intracellular distribution of MAL. The specific reduction and mistargeting of MAL protein as a reaction to sulfatide overload may contribute to the pathogenic mechanisms in metachromatic leukodystrophy.

Metachromatic leukodystrophy: consequences of sulphatide accumulation

Metachromatic leukodystrophy is a lysosomal lipid storage disorder. It is caused by mutations in the gene for arylsulphatase A, an enzyme involved in the degradation of the sphingolipid 3'-O-sulphogalactosylceramide (sulphatide). This membrane lipid can be found in various cell types, but in particularly high concentrations in the myelin of the nervous system. Patients suffer from progressive, finally lethal, demyelination due to accumulation of sulphatide. In the nervous system, lipid storage not only affects oligodendrocytes but also neurons and, in addition, leads to astrogliosis and activation of microglia. At the cellular level, lysosomal sulphatide storage also affects the lipid composition of myelin itself and has consequences for the amount and localization of particular myelin membrane-associated proteins. Here we review data, largely based on an arylsulphatase A knock-out mouse model of metachromatic leukodystrophy.

CONCLUSION

The knock-out mouse model of metachromatic leukodystrophy has provided insights into the histopathological and cellular consequences of sulphatide storage.

Lysosomal sulfoglycolipid storage in the kidneys of mice deficient for arylsulfatase A (ASA) and of double-knockout mice deficient for ASA and galactosylceramide synthase

The inherited deficiency of arylsulfatase A (ASA) causes lysosomal accumulation of sulfoglycolipids (mainly sulfo-galactosylceramide, S-GalCer ) and leads to metachromatic leukodystrophy in humans. Among visceral organs, kidneys are particularly affected. In the present study, the regional distribution and temporal development of sulfoglycolipid storage in kidneys of ASA-/- mice was investigated histochemically (alcian blue) and ultrastructurally. Furthermore, the sulfoglycolipid storage was examined in kidneys of double-knockout mice, which are incapable of: (a) degrading any sulfolipids (ASA-/-) and (b) synthesizing the major sulfolipid S-GalCer because of deficiency for galactosylceramide synthase (CGT), with the aim to search for additional ASA substrates. In ASA-/- mice, the nephron segments could be ranged in the order of decreasing sulfolipid storage: thin limbs of long-looped nephrons approximately thick ascending limbs > distal convoluted tubules > collecting ducts approximately short thin limbs. Macula densa and proximal tubules were unaffected. In ASA-/-/CGT-/- mice, the long thin limbs and distal convoluted tubules resembled those of ASA-/-/CGT+/+ mice, while the other segments showed less storage. The results suggest that the turnover of sulfolipids in general is highest in the distal nephron except macula densa, and that long thin limbs and distal convoluted tubules are the main sites for turnover of a minor sulfolipid species, which is known to be synthesized in the kidney of CGT-/- mice.

Glycosaminoglycan-binding properties and secondary structure of the C-terminus of netrin-1

Netrins are soluble neurite-outgrowth-promoting proteins related to the laminin B2 chain. Since these proteins and their receptor DCC (the "deleted in colorectal carcinoma" gene product) bind heparin, glycosaminoglycans may modulate their biological actions in a similar fashion as described for several other ligand-receptor systems. Here we show that a polypeptide encompassing the C-terminal cluster of basic amino acids of netrin-1 (i) adopts an alpha-helical conformation in water-trifluoroethanol mixtures according to circular dichroism experiments and (ii) binds electrostatically to heparin with high affinity under physiological ionic conditions (K(D) = 15 nM for the binding to immobilized heparin according to surface plasmon resonance, K(D) = 50 nM in solution as determined with isothermal titration calorimetry). These data indicate that the cluster of basic amino acids at the C-terminus of netrin-1 forms an alpha-helical structural element which can contribute to the glycosaminoglycan-binding activity of this neurotrophic guidance molecule.

Binding of selenoprotein P to heparin: characterization with surface plasmon resonance

The binding of selenoprotein P to glycosaminoglycans using heparin as a model compound was studied by surface plasmon resonance. It was found that heparin contains two binding sites for selenoprotein P, a high-affinity, low-capacity site (Kd approximately 1 nM) and a low-affinity, high-capacity site (Kd approximately 140 nM). Binding at both sites is sensitive to pH and ionic strength, and the high-affinity site is abolished by histidine carbethoxylation with diethylpyrocarbonate. The pH and salt dependence of binding suggests electrostatic interactions with heparin. The concentrations of selenoprotein P in plasma (approximately 50 nM) are sufficiently high to facilitate binding of selenoprotein P to proteoglycans on the vascular endothelium, and this may contribute to the formation of a protective barrier against oxidants such as peroxynitrite or hydroperoxides.

Crystallization and preliminary X-ray crystallographic study of the Ras-GTPase-activating domain of human p120GAP

Ras-GTPase-activating proteins (Ras-GAPs) are important regulators of the biological activity of Ras within the framework of intracellular communication where GTP-bound Ras (Ras:GTP) is a key signal transducing molecule (Trahey and McCormick, Science 238:542-545, 1987; Boguski and McCormick, Nature 366:643-654, 1993). By accelerating Ras-mediated GTP hydrolysis, Ras-GAPs provide an efficient means to reset the Ras-GTPase cycle to the GDP-bound 'OFF'-state and terminate the Ras-mediated signal. Here we report the crystallization of the GTPase-activating domain of the human p120GAP. The crystals-belong to the orthorhombic space group symmetry P2(1)2(1)2(1) with unit cell dimensions of a = 42.2 A, b = 55.6 A, c = 142.2 A, alpha = beta = gamma = 90 degrees. Assuming a Matthews parameter of 2.2 A3/Da, there is one molecule per asymmetric unit. Applying micro-seeding techniques, we grew large single crystals that could not be obtained by other routine methods for crystal improvement. They diffracted to a resolution of approximately 3 A using X-rays from a rotating anode generator and to better than 1.8 A in a synchrotron beam. Chemical cross-linking led to reduction of the maximum resolution but to significantly increased stability against mechanical and heavy atom stress.

Studies on the structure and mechanism of H-ras p21

Current knowledge of the structure of H-ras p21 is reviewed with particular emphasis on the interaction between guanine nucleotides and the active site of the protein. The nature of the conformational change induced by GTP hydrolysis is discussed. The major change is seen in the region known as the effector loop (loop 2), with significant but less well-defined changes occurring in loop 4, which is implicated in the GTPase reaction. Other evidence concerning the mechanism of GTP hydrolysis and its activation by GAP (GTPase-activating protein) is also discussed. Evidence regarding the rate limiting step in the p21 GTPase reaction, and the manner in which this and possibly other steps are accelerated by GAP, is inconclusive.

Points of action in the campaign against blindness in developing countries

This article provides a survey of the problems of prevention of blindness in developing countries. The World Health Organization estimates that 31 million people are blind and 15 million people partially-sighted. The main cause of blindness is cataract. Other causes are trachoma, glaucoma, xerophthalmia, river blindness, corneal scars and leprosy. Prevention or treatment of these causes is possible in more than 80% of cases. The number of blind persons, however, is still increasing due to the increase in population and the immense shortage of all kinds of ophthalmological equipment and personnel. An effective strategy for the prevention of blindness in developing countries should focus on: more cheap cataract operations, increasing teaching facilities for ophthalmic personnel, integration of ophthalmic care into the general health system and the promotion of blindness prevention in political organizations.

Alterations of the anterior lens capsule associated with climatic keratopathy

We describe changes in the anterior lens capsules of older people in Somalia, a country which is close to the equator and with large areas of sand, often highly reflective of sunlight. The capsule changes are confined to the central pupillary area. In order of apparently increasing severity they consist of a white opalescence ('frosting'), an elevation in front of the contour of the rest of the lens to form a plateau, and a 'bag' or herniation of the lens capsule through the pupil. Plateau and bagging taken together are strongly associated with climatic keratopathy (and by inference with reflected ultraviolet exposure), weakly associated with exfoliation syndrome, inversely related to the degree of cataract, and interfere severely with vision.

Stereoscopic fluorescein angiography of the fundus

The fundus of the eye is a three-dimensional organ. The usual two-dimensional representation of the angiogram provides us with incomplete information. It is true that it is usually possible by indirect means to deduce at which level the pathological process is taking place, but a simple technique enables one to register and project the angiogram stereoscopically. This gives the observer a direct visual impression of the spatial proportions of the pathological process.