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Biomedical subjects

R B Gordon

Publications and source records attributed to R B Gordon.

At least 19 recordsLinked to original sources
PubMed1999

Cystathionine beta-synthase mutations in homocystinuria.

The major cause of homocystinuria is mutation of the gene encoding the enzyme cystathionine beta-synthase (CBS). Deficiency of CBS activity results in elevated levels of homocysteine as well as methionine in plasma and urine and decreased levels of cystathionine and cysteine. Ninety-two different disease-associated mutations have been identified in the CBS gene in 310 examined homocystinuric alleles in more than a dozen laboratories around the world. Most of these mutations are missense, and the vast majority of these are private mutations. The two most frequently encountered of these mutations are the pyridoxine-responsive I278T and the pyridoxine-nonresponsive G307S. Mutations due to deaminations of methylcytosines represent 53% of all point substitutions in the coding region of the CBS gene.

CpG Islands↗
PubMed1999

Ischemic colitis: CT evaluation of 54 cases.

PURPOSE: To review the computed tomographic (CT) scans and medical records of 54 patients with proved ischemic colitis, define the spectrum of CT findings, and assess the effect of CT imaging on treatment. MATERIALS AND METHODS: The mean age of the patients was 72 years. CT scans were analyzed for the presence of colonic abnormalities and associated findings. Ischemia was clinically unsuspected in 16 patients (30%). RESULTS: Segmental involvement was seen in 48 patients (89%), with a mean length of involvement of 19 cm (range, 5-38 cm). Wall thickness varied between 2 and 20 mm (mean, 8 mm). All parts of the colon were involved. The CT appearance of the colonic wall varied: (a) A wet appearance with heterogeneous areas of edema was seen in 33 patients (61%). (b) A dry appearance with mild homogeneous thickening was seen in 18 patients (33%). (c) Intramural air was present in three patients (6%). Ischemia resolved in 41 patients (76%), and complications occurred in 13 patients (24%). CONCLUSION: CT can be used to confirm the clinical suspicion of ischemic colitis, to suggest ischemia when it is unsuspected, and to diagnose complications. Intrinsic colonic abnormalities cannot be used to diagnose or predict the development of infarction.

Aged↗
PubMed1998

Mutational analysis of the cystathionine beta-synthase gene: a splicing mutation, two missense mutations and an insertion in patients with homocystinuria. Mutations in brief no. 120. Online.

RT-PCR and direct sequence analyses were used to define mutations in the cystathionine beta-synthase (CBS) gene in two unrelated male patients with vitamin B6 nonresponsive homocystinuria. Both patients were compound heterozygotes for CBS alleles containing point mutations. One patient had a maternally derived G->A transition in the splice-donor site of intron 1, resulting in aberrant splicing of CBS mRNA. The other allele contained a missense mutation resulting in the previously reported E144K mutant CBS protein. The second patient had a maternally derived 4 bp insertion in exon 17, predicted to cause a CBS peptide of altered amino acid sequence. A 494G->A transition was found in exon 4 of the other allele, predicting a C165Y substitution. Expression of recombinant CBS protein, containing the C165Y mutation, had no detectable catalytic activity. Each mutation was confirmed in genomic DNA.

Alternative Splicing↗
PubMed1997

Bound Tris confounds the identification of binding site residues in a paraquat single chain antibody.

We produced an anti-paraquat single chain antibody (scFv) to investigate its potential use in immunotherapy for paraquat poisoning. However, this scFv was expressed in an insoluble form and only displayed moderate binding affinity. An earlier examination of the pH dependence of antigen binding by the parent paraquat-specific mAb (7D7-3) suggested that the electrostatic effects of a tyrosine residue were important. The aims of the current study were to obtain expression of a soluble scFv (D10) and to increase its binding affinity. The former was achieved by expression in a phagemid vector. Site-directed mutagenesis of tyrosine residues in CDR H3 did not result in improved affinity for paraquat, suggesting that the original pH dependence required re-examination. Nuclear magnetic resonance studies of 7D7-3 Fab revealed that the original observation of the pH-dependent paraquat binding with a mid-point of approximately pH 8.9 was due to tightly bound Tris. It appears that as Tris is titrated to a neutral species the energetically unfavourable juxtaposition of its positive charge with that of paraquat is reduced. These findings have broad implications in the interpretation of the pH or salt dependence of any antibody-antigen interaction which should be made cautiously and with regard to the possible interference of buffer components introduced during the preparation of the antibody.

Animals↗
PubMed1997

CT of small-bowel lymphoma in immunocompetent patients and patients with AIDS: comparison of findings.

OBJECTIVE: The purpose of this study was to describe and analyze the CT features of small-bowel lymphoma, compare those features with the radiographic presentation in immunocompetent patients and patients with AIDS, and discuss the role of CT in the initial detection and evaluation of this disease. MATERIALS AND METHODS: Abdominal CT examinations of 42 consecutive patients with proven small-bowel lymphoma were retrospectively reviewed. In 19 patients, small-bowel examinations were also available for review. The 42-patient study group was divided into two subgroups: 22 patients with AIDS and 20 immunocompetent patients. RESULTS: Primary small-bowel lymphoma was present in 37% of patients and was equally distributed between the two subgroups. The histologic types included non-Hodgkin's lymphoma in 33 patients, Burkitt's lymphoma in seven patients, Hodgkin's lymphoma in one patient, and mucosa-associated lymphoid tissue-type lymphoma in one patient. Solid organ involvement (liver, splee, kidney, or adrenal glands) was detected in 22% of patients with AIDS and in 10% of the immunocompetent patients. We saw two main patterns of CT appearance. In the first pattern, single or multiple segments had circumferential wall thickening, homogeneous in attenuation, that ranged from 1.5 cm to 7 cm (mean, 2.6 cm) in 33 patients. In the second pattern, single or multiple cavitary lesions were revealed as nodular and grossly enlarged intestinal lumen with bowel wall thickening in 13 patients. A polypoid mass that was entirely intraluminal was seen in one patient. Heterogeneous areas of low attenuation were revealed in two intestinal tumors of HIV-positive patients. Mesenteric or retroperitoneal lymphadenopathy was seen in 45% of patients with AIDS and 60% of the immunocompetent patients. The gross morphologic features, distribution. pattern of CT presentation, degree of wall thickening, and length of involvement were all similar in the two subgroups. CONCLUSION: More than half (52%) of the individuals with small-bowel lymphoma diagnosed at our institution in the last 4 years were patients with AIDS. The features revealed by CT scans were characteristic or highly suggestive of small-bowel lymphoma. We saw no significant differences in the radiographic features of patients with AIDS and immunocompetent patients.

Adult↗
PubMed1996

Human homocysteine catabolism: three major pathways and their relevance to development of arterial occlusive disease.

Two separate metabolic pathways that methylate homocysteine to methionine are known in humans, utilizing, respectively, 5-methyltetrahydrofolate and betaine as methyl donors. Deficiency of the folate-dependent methylation system is linked to hyperhomocysteinemia. Our data suggest that this deficiency leads to concurrent metabolic down-regulation of homocysteine transsulfuration that may contribute to hyperhomocysteinemia. By contrast, no instances have been reported of hyperhomocysteinemia resulting from deficiencies of betaine-dependent homocysteine methylation. Long-term betaine supplementation of 10 patients, who had pyridoxine-resistant homocystinuria and gross hyperhomocysteinemia due to deficiency of cystathionine beta-synthase activity, caused a substantial lowering of plasma homocysteine, which has now been maintained for periods of up to 13 years. Betaine had to be taken regularly because the effect soon disappeared when treatment was stopped. In conclusion, depressed activity of the transsulfuration pathway may contribute to hyperhomocysteinemia because of primary deficiencies of enzymes of either the transsulfuration or of the folate-dependent methylation pathways. Stimulation of betaine-dependent homocysteine remethylation causes a commensurate decrease in plasma homocysteine that can be maintained as long as betaine is taken.

Arterial Occlusive Diseases↗
PubMed1996

Variable hyperhomocysteinaemia phenotype in heterozygotes for the Gly307Ser mutation in cystathionine beta-synthase.

BACKGROUND: A deficiency of cystathionine beta-synthase (CBS) activity is the most frequent cause of homocystinuria, an autosomal recessive disease with multiple clinical manifestations. Mutations in the CBS gene have been reported in several patients with homocystinuria. AIMS: To establish the molecular basis of CBS deficiency in a female patient with pyridoxine non-responsive homocystinuria, and to apply the findings to genetic screening of her family members. METHODS: The entire coding region of the CBS cDNA was amplified by PCR and used for direct sequence analysis. Mutant alleles were confirmed by direct sequence analysis of PCR-amplified genomic DNA, and by a combination of single strand conformation polymorphism and temperature gradient gel electrophoresis analysis. RESULTS: The proband was homozygous for a G919A base transition which predicts the substitution of serine for glycine at codon 307 in the CBS protein (G307S). The parents (both of Irish background) were heterozygotes for the G307S allele, while an asymptomatic sibling had normal CBS sequence, Plasma homocysteine, assessed after an oral methionine load, indicated the mother clearly had moderate hyperhomocysteinaemia, whereas the father had normal concentrations of homocysteine. This is the first report of a normal methionine load test in a proven heterozygote for a CBS mutation which causes severe homocystinuria in the homozygote. Other factor(s) may have contributed to hyperhomocysteinaemia in the mother. The G307S allele has been reported in other patients and appears to be a common allele among families of Celtic origin.

Adolescent↗
PubMed1995

Production of a paraquat-specific murine single chain Fv fragment.

Producing an effective antidote against poisoning by the herbicide paraquat (PQ) has proven to be an elusive goal. One approach that holds some promise is immunotherapy with antibody fragments. In this study we detail the production of a single chain Fv fragment (scFv) specific for paraquat by linking cloned heavy (Vh) and light chain (VL) variable region genes via the peptide spacer (Gly4-Ser)3. These genes were obtained from hybridoma cells secreting a PQ-specific murine monoclonal antibody. The scFv (28 kDa) was expressed at 4% of the total cell protein by the Escherichia coli vector, pPOW, but was associated with the membranes. After solubilization and reduction, the scFv was renatured by rapid dilution. Western blotting confirmed that the refolded scFv had similar structural properties to the parental mAb. The isoelectric point of the scFv (7.0) is equal to the value calculated from the deduced amino acid sequence. Surface plasmon resonance was used to demonstrate specific PQ binding by the refolded scFv(Ka=1.24x10(6)M(-1)) which is similar to that determined for the parent Fab fragment (4.6x10(6)(-1)).

Amino Acid Sequence↗
PubMed1995

A simple method for synthesis of B-cell clonospecific probes.

A sensitive PCR-based method was developed to produce B-cell clonogenic probes without the need for sequencing and specific oligonucleotide synthesis. Specificity and sensitivity were assessed and found to be comparable to that achieved using established methods. Possible applications include the detection of MRD, bone marrow involvement with lymphoma, and the contamination of autologous bone marrow or peripheral blood progenitor cell harvests with malignant cells carrying IgH rearrangements.

Acute Disease↗
PubMed1995

Glutaraldehyde colitis: radiologic findings.

PURPOSE: Two percent glutaraldehyde on colonic mucosa may result in a toxic colitis, and the clinical features may mimic those of colonic ischemia. The study was performed to determine the radiologic appearance of glutaraldehyde-induced toxic colitis. MATERIALS AND METHODS: A retrospective review was performed with the clinical and imaging findings in four patients with glutaraldehyde-induced colitis seen during a 6-year period. RESULTS: Patients developed a self-limited syndrome of cramps and abdominal pain, tenesmus, and rectal bleeding within 48 hours of uncomplicated sigmoidoscopy or colonoscopy. Sample cultures excluded enteric pathogens. Computed tomography (CT) demonstrated circumferential thickening of the colonic wall in a left-sided distribution in all patients. Heterogeneous mural enhancement (target-sign appearance) was noted in two patients. Follow-up CT studies confirmed resolution of mural wall thickening with conservative management. CONCLUSION: The clinical and radiologic features of glutaraldehyde-induced toxic colitis may mimic those of colonic ischemia. This complication should be suspected in patients who develop hemorrhagic colitis immediately after undergoing colonoscopy.

Adult↗
PubMed1992

A review of the molecular basis of hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency.

Hypoxanthine-guanine phosphoribosyltransferase (HPRT, EC 2.4.2.8) is a purine salvage enzyme that catalyses the conversion of hypoxanthine and guanine to their respective mononucleotides. Partial deficiency of this enzyme can result in the overproduction of uric acid leading to a severe form of gout, whilst a virtual absence of HPRT activity causes the Lesch-Nyhan syndrome which is characterised by hyperuricaemia, mental retardation, choreoathetosis and compulsive self-mutilation. The HPRT-encoding gene is located on the X chromosome in the region q26-q27 and consists of nine exons and eight introns totalling 57 kb. This gene is transcribed to produce an mRNA of 1.6 kb, which contains a protein encoding region of 654 nucleotides. With the advent of increasingly refined techniques of molecular biology, it has been possible to study the HPRT gene of individuals with a deficiency in HPRT activity to determine the genetic basis of the enzyme deficiency. Many different mutations throughout the coding region have been described, but in the absence of precise information on the three-dimensional structure of the HPRT protein, it remains difficult to determine any consistent correlation between the structure and function of the enzyme.

Base Sequence↗
PubMed1992

Closed-loop and strangulating intestinal obstruction: CT signs.

In 19 patients with closed-loop intestinal obstruction, including 16 patients with strangulating obstruction, the findings at examination with computed tomography (CT) were retrospectively correlated with the surgical and pathologic findings and evaluated by two radiologists. Signs of closed-loop obstruction, present in 15 patients, were associated with the configuration of the incarcerated loop of small bowel, abnormalities detected at the site of obstruction, or both. These abnormalities were the following: a U-shaped, distended, fluid-filled bowel loop; the whirl sign; the beak sign; a triangular loop; two adjacent collapsed loops of bowel at the site of obstruction; or all of these. CT signs of strangulation, seen in 10 of the 16 patients with ischemic or infarcted bowel, were associated with the appearance of the bowel wall (thickening, high attenuation, and the target sign), abnormalities in the attached mesentery, or both. In mechanical obstruction of the small bowel, detection of ischemic changes in the bowel wall or mesentery with CT indicates strangulation. Absence of CT findings of ischemia or infarction does not rule out strangulation.

Adult↗
PubMed1991

The molecular characterisation of HPRT CHERMSIDE and HPRT COORPAROO: two Lesch-Nyhan patients with reduced amounts of mRNA.

A complete deficiency of the purine salvage enzyme, hypoxanthine phosphoribosyltransferase (HPRT; EC 2.4.2.8), in man results in the Lesch-Nyhan (LN) syndrome. Two unrelated patients with the full LN syndrome showed no evidence of a major alteration to the gene encoding HPRT (HPRT) by restriction endonuclease analysis, but exhibited negligible levels of HPRT mRNA on Northern blots. DNA from these patients was characterised further. Amplification, by the polymerase chain reaction (PCR), of individual HPRT-exon fragments from genomic DNA followed by nucleotide (nt) sequence analysis using automated technology, revealed single-base mutations in each patient. One patient has an insertion of a T within exon-2, which places a stop codon in frame, presumably resulting in premature termination of translation of the HPRT mRNA. The other patient has a G----A base substitution at the 5' end of intron-6, at the junction of exon-6 and intron-6. Although dot blot analysis indicated negligible HPRT mRNA in lymphoblast cells from both patients, we were successful in amplifying HPRT cDNA using PCR. Direct nt sequence analysis of the amplified cDNA confirmed the insertion of a T in exon-2 in the one patient and revealed a complete deletion of exon-6 in the other patient, the latter event presumably arising due to aberrant splicing of primary message. Both mutations were also confirmed by hybridisation of amplified genomic DNA with allele-specific oligodeoxyribonucleotide probes. This study illustrates two approaches for analysing DNA mutations at the molecular level and demonstrates the power of PCR technology in the study of genetic diseases.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1991

Hypoxanthine-guanine phosphoribosyltransferase deficiency: analysis of HPRT mutations by direct sequencing and allele-specific amplification.

The Lesch-Nyhan syndrome is a severe X chromosome-linked human disease caused by a virtual absence of hypoxanthine-guanine phosphoribosyltransferase (HPRT) activity. A partial deficiency in the activity of this enzyme can result in gouty arthritis. To determine the genetic basis for reduction or loss of enzyme activity, we have amplified and sequenced the coding region of HPRT cDNA from four patients: one with Lesch-Nyhan syndrome (HPRTPerth) and three with partial deficiencies of HPRT activity, which have been designated HPRTUrangan, HPRTSwan and HPRTToowong. In all four patients, the only mutation identified was a single base substitution in exons 2 or 3 of the coding region, which in each case predicts a single amino acid substitution in the translated protein. Each base change was confirmed by allele-specific amplification of the patient's genomic DNA. It is interesting to note that the mutation found for HPRTPerth is identical to that reported for HPRTFlint. It appears that the two mutations are de novo events.

Alleles↗