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T W Prior

Publications and source records attributed to T W Prior.

At least 37 records · Page 2Linked to original sources
PubMed1999

Prevalence of the factor VLeiden mutation among autopsy patients with pulmonary thromboembolic disease using an improved method for factor VLeiden detection.

Activated protein C resistance caused by factor VLeiden mutation is the most common inherited predisposing cause of venous thromboembolism, including pulmonary embolism (PE). We studied whether the incidence of factor VLeiden is higher among patients with PE evident at autopsy than in the general population. Paraffin-embedded fixed tissue blocks from all autopsy patients with diagnosed pulmonary thromboembolic disease during a 4-year period were collected for DNA extraction. Extraction and molecular analysis of the DNA was performed with an improved technique with an internal control to determine the presence of factor VLeiden mutation. Analysis of 82 autopsy cases with PE yielded 5 patients who were heterozygotes. Seventy-seven of the 82 patients analyzed were normal, and no homozygotes for factor VLeiden mutation were identified. This yielded a positive rate of 6% overall and 7% among white patients, which is similar to the incidence of heterozygotes in the white population. This study indicates that routine determination of factor VLeiden mutation is not warranted for patients with PE diagnosed at autopsy.

Adolescent↗
PubMed1999

A single nucleotide difference that alters splicing patterns distinguishes the SMA gene SMN1 from the copy gene SMN2.

Spinal muscular atrophy (SMA) is a recessive disorder characterized by loss of motor neurons in the spinal cord. It is caused by mutations in the telomeric survival motor neuron 1 ( SMN1 ) gene. Alterations within an almost identical copy gene, the centromeric survival motor neuron 2 ( SMN2 ) gene produce no known phenotypic effect. The exons of the two genes differ by just two nucleotides, neither of which alters the encoded amino acids. At the genomic level, only five nucleotides that differentiate the two genes from one another have been reported. The entire genomic sequence of the two genes has not been determined. Thus, differences which might explain why SMN1 is the SMA gene are not readily apparent. In this study, we have completely sequenced and compared genomic clones containing the SMN genes. The two genes show striking similarity, with the homology being unprecedented between two different yet functional genes. The only critical difference in an approximately 32 kb region between the two SMN genes is the C->T base change 6 bp inside exon 7. This alteration but not other variations in the SMN genes affects the splicing pattern of the genes. The majority of the transcript from the SMN1 locus is full length, whereas the majority of the transcript produced by the SMN2 locus lacks exon 7. We suggest that the exon 7 nucleotide change affects the activity of an exon splice enhancer. In SMA patients, the loss of SMN1 but the presence of SMN2 results in low levels of full-length SMN transcript and therefore low SMN protein levels which causes SMA.

Alternative Splicing↗
PubMed1999

Identification of MEN1 mutations in sporadic enteropancreatic neuroendocrine tumors by analysis of paraffin-embedded tissue.

Gastrinomas and other gastrointestinal neuroendocrine tumors may occur sporadically or as part of the inherited syndrome multiple endocrine neoplasia type 1 (MEN1). Mutations in the recently identified MEN1 gene have been described in sporadic gastrinomas and insulinomas. This study describes techniques used to identify mutations in the MEN1 gene in DNA extracted from paraffin-preserved tissue. Two novel mutations are identified in the MEN1 gene from nine archived paraffin-embedded neuroendocrine tumors, demonstrating that retrospective genetic analysis can be used to identify mutations in the MEN1 gene from preserved tissue. Conditions are provided by which paraffin-embedded tissue can be used as a source of genetic material for sequence information of sufficient quality for mutational studies of the MEN1 gene. It should also be possible to apply this retrospective genetic analysis of paraffin-embedded tissue to other disease models.

DNA, Neoplasm↗
PubMed1998

Identification of a missense mutation in a Friedreich's ataxia patient: implications for diagnosis and carrier studies.

Approximately 95% of all Friedreich's ataxia (FA) patients are homozygous for a large GAA triplet-repeat expansion in the first intron of the Friedreich's ataxia gene (FRDA). The remaining cases are expected to be compound heterozygous with a GAA expansion on one allele and a point mutation on the other. Generally, the clinical diagnostic profile in this group of patients is indistinguishable from that in classic FA patients with homozygous expansions. This study describes a mildly affected patient who presents with only one expanded allele by Southern blot analysis. Point mutation screening shows a single base change in FRDA exon 3 resulting in a nonconservative amino acid replacement in the N-terminal portion of the frataxin protein. Extended family studies show that two of the patient's sibs are carriers of the expanded allele and one is a carrier of the missense mutation. This case study demonstrates the benefits of implementing a combined Southern blot and point mutation diagnostic protocol for compound heterozygous patients. By identifying both mutations, this procedure confirms the diagnosis of FA in patients with an atypical disease course and allows for more complete family studies.

Adult↗
PubMed1998

Intragenic telSMN mutations: frequency, distribution, evidence of a founder effect, and modification of the spinal muscular atrophy phenotype by cenSMN copy number.

The autosomal recessive neuromuscular disorder proximal spinal muscular atrophy (SMA) is caused by the loss or mutation of the survival motor neuron (SMN) gene, which exists in two nearly identical copies, telomeric SMN (telSMN) and centromeric SMN (cenSMN). Exon 7 of the telSMN gene is homozygously absent in approximately 95% of SMA patients, whereas loss of cenSMN does not cause SMA. We searched for other telSMN mutations among 23 SMA compound heterozygotes, using heteroduplex analysis. We identified telSMN mutations in 11 of these unrelated SMA-like individuals who carry a single copy of telSMN: these include two frameshift mutations (800ins11 and 542delGT) and three missense mutations (A2G, S262I, and T274I). The telSMN mutations identified to date cluster at the 3' end, in a region containing sites for SMN oligomerization and binding of Sm proteins. Interestingly, the novel A2G missense mutation occurs outside this conserved carboxy-terminal domain, closely upstream of an SIP1 (SMN-interacting protein 1) binding site. In three patients, the A2G mutation was found to be on the same allele as a rare polymorphism in the 5' UTR, providing evidence for a founder chromosome; Ag1-CA marker data also support evidence of an ancestral origin for the 800ins11 and 542delGT mutations. We note that telSMN missense mutations are associated with milder disease in our patients and that the severe type I SMA phenotype caused by frameshift mutations can be ameliorated by an increase in cenSMN gene copy number.

Alleles↗
PubMed1998

Diagnosis of spinal muscular atrophy in an SMN non-deletion patient using a quantitative PCR screen and mutation analysis.

We report a child with clinical findings consistent with Werdnig-Hoffmann disease (spinal muscular atrophy type I) who was found not to have the homozygous absence of the survival motor neurone (SMN(T)) gene observed in approximately 95% of spinal muscular atrophy patients. A quantitative PCR based dosage assay for SMN(T) copy number showed that this patient possessed a single copy of the SMN(T) gene. Heteroduplex and sequence analysis of the remaining copy of SMN(T) showed a 2 base pair deletion within exon 4 which produces a frameshift and premature termination of the deduced SMN(T) protein. This protocol of initial SMN(T) gene dosage analysis followed by mutation detection allows identification of SMA compound heterozygotes (patients lacking one copy of SMN(T) and having another mutation in their other copy), thereby increasing the sensitivity of SMA molecular diagnosis.

Cyclic AMP Response Element-Binding Protein↗
PubMed1998

Differential diagnosis of hereditary hemochromatosis from other liver disorders by genetic analysis: gene mutation analysis of patients previously diagnosed with hemochromatosis by liver biopsy.

BACKGROUND: Hereditary hemochromatosis, a common autosomal recessive trait caused by mutations in the HLA-H gene, is often diagnosed by the pathologist at the time of histologic examination. Unfortunately, histologic parameters alone do not differentiate between hereditary hemochromatosis and other causes of iron overload. We performed a retrospective study to determine the frequency of familial hemochromatosis in patients diagnosed with he mochromatosis by abnormal liver histology. METHODS AND RESULTS: DNA was isolated from paraffin-embedded tissue sections from 15 patients and used in a polymerase chain reaction-based assay in which we tested for the C282Y and H63D mutations. We found that in this group of patients, 5 (33%) were homozygous for the common C282Y genetic mutation, 3 (20%) were heterozygous, and 7 (47%) were normal. CONCLUSIONS: Our study shows that the molecular assay is the gold standard for the diagnosis of hereditary hemochromatosis. The case study also illustrates that a definitive diagnosis of familial hemochromatosis has significant counseling implications allowing for accurate family studies.

Adult↗
PubMed1997

Deletion and conversion in spinal muscular atrophy patients: is there a relationship to severity?

The spinal muscular atrophy-determining gene, survival motor neuron (SMN), is present in two copies, telSMN and cenSMN, which can be distinguished by base-pair changes in exons 7 and 8. The telSMN gene is often absent in spinal muscular atrophy patients, which could be due to deletion or sequence conversion (telSMN conversion to cenSMN giving rise to two cenSMN genes). To test for conversion events in spinal muscular atrophy, we amplified a 1-kb fragment that spanned exons 7 and 8 of SMN from 5 patients who retained telSMN exon 8 but lacked exon 7. In all patients, sequence analysis demonstrated that cenSMN exon 7 was adjacent to telSMN exon 8, indicating conversion. All 5 patients with this mutation had type II or III spinal muscular atrophy, strongly supporting an association with chronic spinal muscular atrophy. We also identified 3 families in which 2 siblings had no detectable telSMN but presented with markedly different phenotypes. We suggest that sequence conversion is a common event in spinal muscular atrophy and is associated with the milder form of the disease. The severity, however, can be modified in either a positive or negative direction by other factors that influence splicing or expression of the sequence converted SMN gene.

Base Sequence↗
PubMed1997

Molecular diagnosis of non-deletion SMA patients using quantitative PCR of SMN exon 7.

The telomeric survival motor neuron (SMN(T)) gene is a valuable molecular diagnostic tool for childhood-onset spinal muscular atrophy (SMA) as homozygous deletions of SMN(T) exon 7 (delta7SMN(T)) are present in approximately 94% of patients. In this report, we provide the first comprehensive study of 32 unrelated non-deletion SMA patients. Quantitative polymerase chain reaction (PCR) studies established that 90% had two intact copies of SMN(T) exon 7 suggesting that these patients do not have 5q SMA. Once 5q SMA is confirmed, the SMN(T) gene can be screened for subtle mutations. Using single strand conformation analysis, we identified two missense mutations (P245L and Y272C) in exon 6 of the SMN(T) gene of two SMA patients shown to have a single copy of SMN(T) exon 7. Y272 is most likely critical for SMN(T) function as it is a target for recurring mutations and is associated with type I SMA. These results emphasize the need for dosage analysis in the differential diagnosis of 5q SMA in nondeletion patients, consistent with extensive clinical heterogeneity and some genetic heterogeneity in this disease. Homozygosity or heterozygosity for a delta7SMN(T) allele confirms the diagnosis of 5q SMA with greater precision than clinical examination alone.

Amino Acid Substitution↗
PubMed1997

Issues related to DNA testing for Huntington's disease in symptomatic patients.

The DNA test for Huntington's disease simplifies diagnosis, but does not eliminate clinical and ethical issues. Records of 80 consecutive patients who had testing were reviewed; 54 had a positive result. We present seven examples of the variety of problems disclosed by our review. Among the issues that remain unsettled are: (1) Who should do needed counseling and how much? (2) When, if ever, is presymptomatic testing for this incurable disease indicated? (3) Should the patient have access to information about the length of repeats, as the age of onset is affected by the length of repeat? (4) Is it true that insurance companies or relatives have no right to learn the results of DNA testing on a patient?

Adult↗
PubMed1997

Identification of proximal spinal muscular atrophy carriers and patients by analysis of SMNT and SMNC gene copy number.

The survival motor neuron (SMN) transcript is encoded by two genes, SMNT and SMNC. The autosomal recessive proximal spinal muscular atrophy that maps to 5q12 is caused by mutations in the SMNT gene. The SMNT gene can be distinguished from the SMNC gene by base-pair changes in exons 7 and 8. SMNT exon 7 is not detected in approximately 95% of SMA cases due to either deletion or sequence-conversion events. Small mutations in SMNT now have been identified in some of the remaining nondeletion patients. However, there is no reliable quantitative assay for SMNT, to distinguish SMA compound heterozygotes from non-5q SMA-like cases (phenocopies) and to accurately determine carrier status. We have developed a quantitative PCR assay for the determination of SMNT and SMNC gene-copy number. This report demonstrates how risk estimates for the diagnosis and detection of SMA carriers can be modified by the accurate determination of SMNT copy number.

Amino Acid Sequence↗
PubMed1997

The survival motor neuron protein in spinal muscular atrophy.

The 38 kDa survival motor neuron (SMN) protein is encoded by two ubiquitously expressed genes: telomeric SMN (SMN(T)) and centromeric SMN (SMN(C)). Mutations in SMN(T), but not SMN(C), cause proximal spinal muscular atrophy (SMA), an autosomal recessive disorder that results in loss of motor neurons. SMN is found in the cytoplasm and nucleus. The nuclear form is located in structures termed gems. Using a panel of anti-SMN antibodies, we demonstrate that the SMN protein is expressed from both the SMN(T) and SMN(C) genes. Western blot analysis of fibroblasts from SMA patients with various clinical severities of SMA showed a moderate reduction in the amount of SMN protein, particularly in type I (most severe) patients. Immunocytochemical analysis of SMA patient fibroblasts indicates a significant reduction in the number of gems in type I SMA patients and a correlation of the number of gems with clinical severity. This correlation to phenotype using primary fibroblasts may serve as a useful diagnostic tool in an easily accessible tissue. SMN is expressed at high levels in brain, kidney and liver, moderate levels in skeletal and cardiac muscle, and low levels in fibroblasts and lymphocytes. In SMA patients, the SMN level was moderately reduced in muscle and lymphoblasts. In contrast, SMN was expressed at high levels in spinal cord from normals and non-SMA disease controls, but was reduced 100-fold in spinal cord from type I patients. The marked reduction of SMN in type I SMA spinal cords is consistent with the features of this motor neuron disease. We suggest that disruption of SMN(T) in type I patients results in loss of SMN from motor neurons, resulting in the degeneration of these neurons.

Animals↗
PubMed1997

Dystrophin expression in a Duchenne muscular dystrophy patient with a frame shift deletion.

The exon 45 deletion is a common dystrophin gene deletion. Although this is an out-of-frame deletion, which should not allow for protein synthesis, it has been observed in mildly affected patients. We describe a patient with an exon 45 deletion who produced protein, but still had a severe Duchenne muscular dystrophy phenotype. RT-PCR analysis and cDNA sequencing from the muscle biopsy sample revealed that the exon 45 deletion induced exon skipping of exon 44, which resulted in an in-frame deletion and the production of dystrophin. A conformational change in dystrophin induced by the deletion is proposed as being responsible for the severe phenotype in the patient. We feel that the variable clinical phenotype observed in patients with the exon 45 deletion is not due to exon splicing but may be the result of other environmental or genetic factors, or both.

Base Sequence↗
PubMed1997

Detection of viral DNA in vestibular ganglia tissue from patients with Menière's disease.

OBJECTIVE: The main goal of this study was to examine the vestibular ganglia from 11 patients with intractable classic Menière's disease (MD) for the presence or absence of DNA from three neurotropic viruses (herpes simplex virus, cytomegalovirus, and varicella zoster virus) using exquisitely sensitive molecular biologic techniques. STUDY DESIGN: This was a prospective controlled study with vestibular ganglia from patients with MD and from patients with small vestibular schwannomas undergoing resection. Polymerase chain reaction was used for viral DNA detection from the ganglia along with known positive and negative polymerase chain reaction control subjects. SETTING: The study was performed in an academic tertiary referral center. PATIENTS: Patients for inclusion had medically uncontrolled MD, including documented fluctuating sensorineural hearing loss, episodic vertigo, and tinnitus who elected to undergo vestibular nerve section. Control patients were undergoing vestibular schwannoma removal. INTERVENTIONS: The intervention was vestibular nerve section with removal of vestibular ganglion. MAIN OUTCOME MEASURES: The presence or absence of viral DNA (herpes simplex virus, cytomegalovirus, and varicella zoster virus) in vestibular ganglion tissues detected by polymerase chain reaction. RESULTS: No viral DNA was detected in the vestibular ganglia of patients with MD (p = 0.028) nor in the control group. The likelihood of a type II or beta type error was < 10%. CONCLUSIONS: In patients with MD requiring surgical intervention, infection with herpes simplex virus, cytomegalovirus, or varicella zoster virus of the vestibular ganglia does not appear to play a major role in the pathoetiology of the disease.

Base Sequence↗
PubMed1996

The incidence of the gene for thermolabile methylene tetrahydrofolate reductase in African Americans.

Increased levels of homocysteine have been linked to both arterial and venous thromboembolic problems (1,2). Homocystinuria is a relatively rare disorder caused by a deficiency of cystathione synthase and is characterized by markedly increased levels of homocysteine and premature vascular disease (3-5). Epidemiological studies have suggested that mild elevations of homocysteine are also associated with vascular disease (2). Recent evidence suggests that a polymorphism of the gene encoding for 5,10-methylene tetrahydrofolate reductase (MTHFR) gives rise to a thermolabile form of the enzyme that is associated with increased levels of homocysteine when inherited as a homozygous trait (6). This polymorphism is due to a C --> T substitution at nucleotide 677 which converts an alanine to valine in a conserved portion of the molecule (6). The allele frequency for the thermolabile form of the enzyme was quite high (0.38) in a population of French Canadians. This polymorphism thus appears to be a common risk factor for increased plasma levels of homocysteine and vascular diseases. As the incidence of such genetic polymorphisms often varies among ethnic populations, we were interested in comparing the incidence of this polymorphism in Caucasians and African Americans.

Black or African American↗
PubMed1996

Mutational spectrum in the neurofibromatosis type 2 gene in sporadic and familial schwannomas.

Using a heteroduplex approach and direct sequencing, we have completed the screening of approximately 88% of the neurofibromatosis type 2 (NF2)-coding sequence of DNA extracted from 33 schwannomas from NF2 patients and from 29 patients with sporadic schwannomas. The extensive screening has resulted in the identification of 33 unique mutations. Similarly to other human genes, we have shown that the CpG sites are more highly mutable in the NF2 gene. The frequency, distribution, and types of mutations were shown to differ between the sporadic and familial tumors. The majority of the mutations resulted in protein truncation and were consistent with more severe phenotype, however three missense mutations were identified during this study and were all associated with milder manifestations of the disease.

Codon↗