Gene conversion is a likely cause of mutation in PKD1

Approximately 70% of the gene responsible for the most common form of autosomal dominant polycystic kidney disease ( PKD1 ) is replicated in several highly homologous copies located more proximally on chromosome 16. We recently have described a novel technique for mutation detection in the duplicated region of PKD1 that circumvents the difficulties posed by these homologs. We have used this method to identify two patients with a nearly identical cluster of base pair substitutions in exon 23. Since pseudogenes are known to be reservoirs for mutation via gene conversion events for a number of other diseases, we decided to test whether these sequence differences in PKD1 could have arisen as a result of this mechanism. Using changes in restriction digest patterns, we were able to show that these sequence substitutions are also present in N23HA, a rodent-human somatic cell hybrid that contains only the PKD1 homologs. Moreover, these changes were also detected in total DNA from several affected and unaffected individuals that did not harbor this mutation in their PKD1 gene copy. This is the first example of gene conversion in PKD1 , and our findings highlight the importance of using gene-specific reagents in defining PKD1 mutations.      

Shwachman syndrome: Exocrine pancreatic dysfunction and variable phenotypic expression

BACKGROUND & AIMS: Shwachman syndrome is an inherited condition with multisystemic abnormalities, including exocrine pancreatic dysfunction. The aim of this study was to evaluate the occurrence and progression of features in a large cohort of patients. METHODS: Clinical records of 25 patients with Shwachman syndrome were reviewed. RESULTS: Mean birth weight (2.92 +/- 0.51 kg) was at the 25th percentile. However, by 6 months of age, mean heights and weights were less than the 5th percentile. After 6 months of age, growth velocity was normal. Severe fat maldigestion due to pancreatic insufficiency was present in early life (fecal fat, 26% +/- 17% of fat intake; age, < 2 years). Serial assessment of exocrine pancreatic function showed persistent deficits of enzyme secretion, but 45% of patients showed moderate age-related improvements leading to pancreatic sufficiency. Neutropenia was the most common hematologic abnormality (88%), but leukopenia, thrombocytopenia, and anemia were also frequently encountered. Patients with hypoplasia of all three bone marrow cellular lines (n = 11) had the worst prognosis; 5 patients died, 2 of sepsis and 3 of acute myelogenous leukemia. Other findings included hepatomegaly and/or abnormal liver function test results and skeletal abnormalities. CONCLUSIONS: A wide and varied spectrum of phenotypic abnormalities among patients with Shwachman syndrome is described. Pancreatic acinar dysfunction is an invariable abnormality. Patients with severe bone marrow involvement may have a guarded prognosis. (Gastroenterology 1996 Dec;111(6):1593-602)     

Prostaglandin E2 potentiates platelet aggregation by priming protein kinase C

Prostaglandin E2 (PGE2) is produced by activated platelets and by several other cells, including capillary endothelial cells. PGE2 exerts a dual effect on platelet aggregation: inhibitory, at high, supraphysiologic concentrations, and potentiating, at low concentrations. No information exists on the biochemical mechanisms through which PGE2 exerts its proaggregatory effect on human platelets. We have evaluated the activity of PGE2 on human platelets and have analyzed the second messenger pathways involved. PGE2 (5 to 500 nmol/L) significantly enhanced aggregation induced by subthreshold concentrations of U46619, thrombin, adenosine diphosphate (ADP), and phorbol 12-myristate 13-acetate (PMA) without simultaneously increasing calcium transients. At a high concentration (50 mumol/L), PGE2 inhibited both aggregation and calcium movements. PGE2 (5 to 500 nmol/L) significantly enhanced secretion of beta-thromboglobulin (beta TG) and adenosine triphosphate from U46619- and ADP-stimulated platelets, but it did not affect platelet shape change. PGE2 also increased the binding of radiolabeled fibrinogen to the platelet surface and increased the phosphorylation of the 47-kD protein in 32P- labeled platelets stimulated with subthreshold doses of U46619. Finally, the amplification of U46619-induced aggregation by PGE2 (500 nmol/L) was abolished by four different protein kinase C (PKC) inhibitors (calphostin C, staurosporine, H7, and TMB8). Our results suggest that PGE2 exerts its facilitating activity on agonist-induced platelet activation by priming PKC to activation by other agonists. PGE2 potentiates platelet activation at concentrations produced by activated platelets and may thus be of pathophysiologic relevance.     

From the Cover: Accumulation and enhanced cycling of polyphosphate by Sargasso Sea plankton in response to low phosphorus

Phytoplankton alter their biochemical composition according to nutrient availability, such that their bulk elemental composition varies across oceanic provinces. However, the links between plankton biochemical composition and variation in biogeochemical cycling of nutrients remain largely unknown. In a survey of phytoplankton phosphorus stress in the western North Atlantic, we found that phytoplankton in the phosphorus-depleted subtropical Sargasso Sea were enriched in the biochemical polyphosphate (polyP) compared with nutrient-rich temperate waters, contradicting the canonical oceanographic view of polyP as a luxury phosphorus storage molecule. The enrichment in polyP coincided with enhanced alkaline phosphatase activity and substitution of sulfolipids for phospholipids, which are both indicators of phosphorus stress. Further, polyP appeared to be liberated preferentially over bulk phosphorus from sinking particles in the Sargasso Sea, thereby retaining phosphorus in shallow waters. Thus, polyP cycling may form a feedback loop that attenuates the export of phosphorus when it becomes scarce, contributes bioavailable P for primary production, and supports the export of carbon and nitrogen via sinking particles.Phosphorus (P) is an essential element for all living organisms. However, P can be extremely scarce in open-ocean surface waters such as in the subtropical western North Atlantic (the Sargasso Sea), where soluble reactive P (SRP) concentrations are routinely <10 nmol⋅L⁻¹ and turnover rates are on the order of hours (1). Despite this scarcity, primary production by phytoplankton in the Sargasso Sea does not appear to be limited primarily by P (2, 3), reflecting the intensity of P recycling by the microbial community (4, 5) and the exquisite adaptations of marine phytoplankton to low P conditions, which remain to be fully characterized.Phytoplankton respond to low P by producing enzymes such as alkaline phosphatase to hydrolyze extracellular dissolved organic P molecules (4, 6, 7), increasing the affinity and rate of P uptake (8, 9) and reducing their inventory of P-containing biochemicals (1, 10). In contrast, when P is abundant, phytoplankton take up excess P and store it as a luxury reserve that is generally thought to be composed of polyphosphate (polyP) (10–12). This modulation of P-containing biochemicals results in basin-scale relationships between P availability and biomass carbon-to-phosphorus (C:P) ratios (13). Presently, the only class of molecules known to consistently contribute to these gradients in cellular P are lipids because P stress in phytoplankton triggers substitution of non–P-membrane lipids for phospholipids, such as the sulfolipid sulfoquinovosyldiacylglycerol (SQDG) for the phospholipid phosphatidylglycerol (PG) (1, 14). However, lipid substitution alone probably cannot account for the full range of C:P observed in the ocean, and yet an understanding of other biochemical drivers of the C:P gradient remains elusive. Further, it is unknown how changes in plankton biochemical composition influence the recycling of nutrients.Polyphosphate (polyP), a ubiquitous inorganic P polymer of three to hundreds of residues, has diverse physiological roles and complex dynamics in microbes. It is critical for surviving nutritional stress and stationary phase (15–17) but is also important for P homeostasis: microbes produce polyP when P is more abundant than required for growth, so-called luxury uptake, and break down this polyP store upon P stress (18). Moreover, if P-stressed cells experience a spike in P availability, they overproduce polyP in excess of luxury uptake levels, the so-called “overplus” response (19). Given these complex dynamics, it has been hypothesized that polyP might be either virtually absent, or particularly abundant, in oligotrophic marine systems (20).     

Interleukin-6 enhances growth factor-dependent proliferation of the blast cells of acute myeloblastic leukemia

The effects of recombinant interleukin-6 (IL-6) on the proliferation of blast precursors present in the peripheral blood of patients with acute myeloblastic leukemia (AML) was investigated. IL-6 had little effect by itself; however, it synergized with granulocyte macrophage colony- stimulating factor (GM-CSF) and interleukin-3 (IL-3) in the stimulation of AML blast colony formation. Responsiveness of blast progenitors to IL-6 was heterogeneous. On normal bone marrow cells the same synergy was observed on granulocyte and monocyte precursors (GM-CFC), while there was no significant effect on erythroid and multipotential precursors.     

Glutaric aciduria type II: treatment with riboflavine,carnitine and insulin

A boy, now 22 months old, is described who presented at the age of 6 weeks with hypoglycaemic coma. The excretion pattern of organic acids in the urine was consistent with glutaric aciduria type II (GA II). A high energy diet low in fat and protein was given.Treatment with riboflavine resulted in an improvement of the metabolite profile, and the patient gained weight. However, a tendency to hypoglycaemia and severe hypotonia persisted. Due to muscle weakness, aggravated by infections, artificial ventilation was necessary during three periods.Serum carnitine level was low. Treatment with carnitine, started during the third period of artificial ventilation, led to some improvement of muscle strength, but he still could not breathe without support. Treatment with insulin, combined with further enrichment of the diet with glucose, resulted in an increase in muscular strength and in weight gain.Thirteen families with GA II have been described upto now. This is the first patient with a severe form of the disorder wo has survived the 1st year of life. Treatment and metabolic studies are presented.     

Perinatally ruptured dermoid cyst presenting as congenital oculomotor palsy

An eight-month-old girl presented with congenital exotropia and latent nystagmus. Further evaluation revealed congenital ptosis of the left eye and restriction of the elevation, depression and adduction of the left eye. A diagnosis of congenital oculomotor palsy was made. At the age of three months she had been examined by the neurologist because of retarded psychomotor development. All laboratory investigations were normal. At the age of eight months, a CT scan of the brain and orbit was found to be normal. The patient was treated for amblyopia. At the age of five, strabismus surgery was performed, and a large fibrous tumor encapsulating the superior and lateral rectus muscle was found. A biopsy was taken and pathology showed fibrous tissue containing a hair. Based on the clinical history, the diagnosis of a perinatally ruptured orbital dermoid cyst was made. Review of the previous CT and an additional CT showed enlargement of the left lateral orbital wall with a notch in the lateral wall, indicative of a dermoid cyst.     

Child abuse study among Swedish physicians and medical students

Background: The purpose of the present paper was to examine the attitudes and experiences of reporting child abuse and neglect among primary care and hospital‐based physicians and to study the responses of physicians and medical students to case vignettes suggestive of possible physical abuse or neglect. Methods: Physicians at the child health centers in Göteborg primary care (n= 44) and the general pediatricians at the pediatric hospital (n= 21) in Göteborg answered a questionnaire regarding their attitude and experiences reporting child abuse and neglect. The physicians and medical students (n= 34) responded to three case vignettes in which child abuse and neglect could be suspected. Results: A majority of the physicians had reported child abuse and neglect to the social services (80%). No differences were found between primary care and hospital‐based physicians in terms of reporting or attitudes. Two‐thirds of the physicians had suspected child abuse and neglect and decided not to report, and the major reason for not reporting was a lack of confidence in social services organization. Twenty‐one percent had never reported a child for abuse or neglect during their working career. Medical students were more likely to report hypothetical cases than physicians. Conclusion: Many physicians have reported child abuse to social services but also have neglected to do so even when suspecting abuse. It is important that medical students’ willingness to report is continued when starting to work clinically and that all physicians should be continuously educated.