Impact of national guidelines on family history breast cancer surveillance.

The breast cancer risk of women already under family history surveillance was accurately assessed according to national guidelines in an attempt to rationalize the service. Women attending two breast units in Glasgow between November 2003 and February 2005 were included. One thousand and five women under annual surveillance were assessed and had their relatives diagnoses verified. Four hundred and ninety-seven women were at significantly increased risk and eligible for follow-up. Five hundred and eight (50%) women attending were not eligible for family history surveillance, and 498 (98%) of these women accepted discharge. In conclusion, national guidelines have helped to more clearly define women who should undergo surveillance. This avoids unnecessary and potentially harmful routine investigations, and the service has been improved.

Molecular basis of sulfite oxidase deficiency from the structure of sulfite oxidase.

The molybdenum-containing enzyme sulfite oxidase catalyzes the conversion of sulfite to sulfate, the terminal step in the oxidative degradation of cysteine and methionine. Deficiency of this enzyme in humans usually leads to major neurological abnormalities and early death. The crystal structure of chicken liver sulfite oxidase at 1.9 A resolution reveals that each monomer of the dimeric enzyme consists of three domains. At the active site, the Mo is penta-coordinated by three sulfur ligands, one oxo group, and one water/hydroxo. A sulfate molecule adjacent to the Mo identifies the substrate binding pocket. Four variants associated with sulfite oxidase deficiency have been identified: two mutations are near the sulfate binding site, while the other mutations occur within the domain mediating dimerization.

Isolated sulfite oxidase deficiency.

Isolated sulfite oxidase (SO) deficiency is an autosomal recessively inherited inborn error of sulfur metabolism. In this report of a ninth patient the clinical history, laboratory results, neuropathological findings and a mutation in the sulfite oxidase gene are described. The data from this patient and previously published patients with isolated sulfite oxidase deficiency and molybdenum cofactor deficiency are summarized to characterize this rare disorder. The patient presented neonatally with intractable seizures and did not progress developmentally beyond the neonatal stage. Dislocated lenses were apparent at 2 months. There was increased urine excretion of sulfite and S-sulfocysteine and a decreased concentration of plasma cystine. A lactic acidemia was present for 6 months. Liver sulfite oxidase activity was not detectable but xanthine dehydrogenase activity was normal. The boy died of respiratory failure at 32 months. Neuropathological findings of cortical necrosis and extensive cavitating leukoencephalopathy were reminiscent of those seen in severe perinatal asphyxia suggesting an etiology of energy deficiency. A point mutation that resulted in a truncated protein missing the molybdenum-binding site has been identified.

Site-directed mutagenesis of recombinant sulfite oxidase: identification of cysteine 207 as a ligand of molybdenum.

Each of the four cysteines in rat sulfite oxidase was altered by site-directed mutagenesis to serine, and the mutant proteins were expressed in Escherichia coli. Three of the replacements proved to be silent mutations, while a single cysteine, Cys-207, was found to be essential for enzyme activity. The C207S mutation was also generated in cloned human sulfite oxidase. The mutant human enzyme also displayed severely attenuated activity but was expressed at higher levels allowing purification and spectroscopic analysis. The absorption spectrum of the isolated molybdenum domain of the human C207S mutant displayed marked attenuation of the peak at 350 nm and a lesser decrease in absorbance from 450-600 nm as compared with the native human molybdenum domain. The molybdenum and molybdopterin contents of the two samples were comparable. These data suggest that the major features in the absorption spectrum of the native molybdenum domain arise from the binding of Cys-207 to the molybdenum and indicate that this residue functions as a ligand of the metal.

Molecular cloning of human liver sulfite oxidase.

A 2.4 kilobase cDNA clone of human sulfite oxidase was isolated from a human liver cDNA library in lambda gt10. Comparison of three sulfite oxidase sequences to several plant and fungal nitrate reductase sequences reveals a single conserved cysteine with highly conserved flanking sequences. The conserved cysteine is postulated to be a ligand of molybdenum in sulfite oxidase and nitrate reductase.

Molecular cloning of rat liver sulfite oxidase. Expression of a eukaryotic Mo-pterin-containing enzyme in Escherichia coli.

The cDNA encoding sulfite oxidase has been cloned from a rat liver cDNA library. The gene contains a single open reading frame of 1464 nucleotides encoding a protein of 488 amino acids. The deduced amino acid sequence contains a 22-residue amino-terminal presequence that may serve as a mitochondrial targeting signal. The amino acid sequence deduced from the cDNA shows significant similarity to those of sulfite oxidase from chicken liver and nitrate reductases from algal, fungal, and plant sources. Two cysteine residues are conserved in all of these proteins, and it is proposed that one or both of these cysteines serve as ligands to molybdenum. The gene has been expressed in Escherichia coli to a level equivalent to that observed in rat liver. The recombinant enzyme has been found to contain the molybdopterin form of the molybdenum cofactor and is active as determined by the sulfite dependent reduction of cytochrome c.