The iron uptake mechanisms of enteropathogenic Escherichia coli: the use of haem and haemoglobin during growth in an iron-limited environment.

The iron uptake mechanisms of enteropathogenic Escherichia coli (EPEC) were examined and compared with those of control E. coli strains. The incidence of aerobactin production was similar (39% and 37% respectively) in the two groups. The quantities of enterochelin produced by aerobactin-negative EPEC and control strains were similar, as were the quantities of enterochelin produced by aerobactin-positive EPEC and control strains. The ability to use haem or haemoglobin as an iron source in an iron-restricted environment was found in 80.4% and 60.8% of EPEC strains respectively, and in 76.6% and 56.6% of control E. coli strains. The ability of E. coli strains to use these compounds was not related to the production of enterochelin or aerobactin or to the production of haemolysins, and may be an important characteristic of bowel organisms. When growing in an iron-limited environment, the iron contained in haemoglobin was used in preference to ovotransferrin-bound iron. During periods of haemoglobin-stimulated growth, the enterochelin uptake system was shown to be fully expressed and may be involved in transport of haemoglobin-derived iron into the cell. Uptake of ovotransferrin-bound iron took place immediately upon exhaustion of haemoglobin-derived iron. The ability to use iron derived from haem compounds represents an alternative iron uptake mechanism for organisms growing in an iron-limited environment and allows greater flexibility during growth in vivo.     

A cytogenetic deletion, del(17)(q11.22q21.1), in a patient with sporadic neurofibromatosis type 1 (NF1) associated with dysmorphism and developmental delay.

We report the first visible cytogenetic deletion involving the NF1 gene in a patient with sporadic neurofibromatosis, dysmorphic features, and marked developmental delay. The combined evidence of molecular and cytogenetic techniques based on dosage reduction, hemizygosity for microsatellite markers, high resolution G banding, and FISH analysis, predicts this deletion to be approximately 7 Mb in size. Our findings highlight the importance of conducting a detailed cytogenetic and FISH analysis in patients with NF1 who have additional dysmorphic features or particularly severe learning difficulties.     

Dicentric chromosome in the bone marrow of a child with megakaryoblastic leukaemia and Down''s syndrome.

A two year old girl with Down's syndrome (constitutional karyotype: 47 + 21), presenting with pancytopenia, developed acute megakaryoblastic leukaemia (AMKL). Her bone marrow contained an abnormal clone with a novel dicentric chromosome derived from chromosomes 5 and 7 (karyotype 46, XX, -5, -7, +dic (5;7) (p 13; p 11.2), +21. This case provides further evidence for a connection between chromosome 21 and this unusual form of childhood leukaemia, and raises questions about the loss of short arm material from chromosomes 5 and 7 compared with the more usual monosomy or long arm loss.     

A further mutation of the FGFR2 tyrosine kinase domain in mild Crouzon syndrome

We report a family heterozygous for a newly identified mutation in the tyrosine kinase I domain of the FGFR2 gene (1576A > G, encoding the missense substitution Lys526Glu), associated with variable expressivity of Crouzon syndrome, including clinical nonpenetrance. Our observations expand both the clinical and molecular spectrum of this unusual subset of FGFR2 mutations.     

Functional characterization of missense mutations at codon 838 in retinal guanylate cyclase correlates with disease severity in patients with autosomal dominant cone-rod dystrophy

Three different mutations in codon 838 of GUCY2D, the gene for retinal guanylate cyclase 1, have been linked to autosomal dominant cone-rod dystrophy at the CORD6 locus. To examine the relationship between enzyme activity and disease severity, the three disease-causing substitutions (R838C, R838H and R838S) and four artificial mutations (R838A, R838E, R838L and R838K) were generated. Assay of GCAP1-stimulated cyclase activity in vitro shows that, compared with wild-type, R838E, R838L and R838K possess only low activity, whereas R838A, R838C, R838H and R838S have activity equal or superior to wild-type at low Ca(2+) concentrations. These four latter mutants showed a higher apparent affinity for GCAP1 than did wild-type. The Ca(2+) sensitivity of the GCAP1 activation was also altered with marked residual activity at high Ca(2+), the effect increasing: wild-type < R838C < R838H < R838A < R838S. Within the photoreceptor, this would result in a failure to inactivate cyclase activity at high physiological Ca(2+ )concentrations. Amongst the three disease-associated mutations, the effect correlates directly with disease severity. The wild-type and R838H mutant displayed a difference in pH sensitivity, with the mutant showing a higher specific activity with pH > 6.0. Site 838 is in the dimerization domain that forms a coiled-coil in the active protein. A computer-aided structure prediction of this region indicates that R838 in the wild-type breaks the structure at four helical turns, and there is an increasing tendency for the structure to continue for further turns in the order R838C < R838H,S,K < R838E < R838A < R838L.     

Ramp rate of blood pressure changes does not affect aortic afferent sensitivity in anesthetized rats

To investigate whether the rate of change in blood pressure affects the sensitivity of the aortic baroreceptor afferent response, the change in aortic nerve activity (ANA) to two different rates of ramp increase in mean blood pressure (MBP), elicited by phenylephrine administration, was determined in the rat under urethane (1.5 g kg⁻¹) anesthesia. The sensitivity of the increase in ANA following a rapid (average ramp rate, 9.14 ± 0.60 mmHg s⁻¹, n = 11) or gradual (1.78 ± 0.24 mmHg s⁻¹, n = 11) increase in MBP was 2.03 ± 0.14% and 1.81 ± 0.20% of baseline mmHg⁻¹, respectively. These values were not significantly different from each other (P = 0.16). Furthermore, we found no correlation between the rate of ramp increase in MBP and the sensitivity of the increase in ANA (r = 0.24, P = 0.29, n = 22). These results suggest that, at least within the normal physiological range of MBP, the rate of the ramp change in blood pressure does not affect aortic baroreceptor afferent sensitivity in the anesthetized rat.