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K Snow

Publications and source records attributed to K Snow.

At least 19 recordsLinked to original sources
PubMed2001

Niemann-Pick C variant detection by altered sphingolipid trafficking and correlation with mutations within a specific domain of NPC1.

Niemann-Pick disease type C (NPC) is a fatal, autosomal recessive lipidosis characterized by lysosomal accumulation of unesterified cholesterol and multiple neurological symptoms, such as vertical supranuclear ophthalmoplegia, progressive ataxia, and dementia. More than 90% of cases of NPC are due to a defect in Niemann-Pick C1 (NPC1), a late endosomal, integral membrane protein that plays a role in cholesterol transport or homeostasis. Biochemical diagnosis of NPC has relied on the use of patient skin fibroblasts in an assay to demonstrate delayed low-density lipoprotein (LDL)-derived cholesterol esterification and a cytological technique-filipin staining-to demonstrate the intracellular accumulation of cholesterol. A small percentage of patients, referred to as "NPC variants," present with clinical symptoms of NPC but show near-normal results of these biochemical tests, making laboratory confirmation of NPC disease problematic. Here, we demonstrate that NPC-variant fibroblast samples can be detected as sphingolipid storage disease cells, using a fluorescent sphingolipid analog, BODIPY-lactosylceramide. This lipid accumulated in endosomes/lysosomes in variant cells preincubated with LDL cholesterol but targeted to the Golgi complex in normal cells under these conditions. The reproducibility of this technique was validated in a blinded study. In addition, we performed mutation analysis of the NPC1 gene in NPC variant and "classical" NPC cell samples and found a high incidence of specific mutations within the cysteine-rich region of NPC1 in variants. We also found that 5 of the 12 variant cell samples had no apparent defect in NPC1 but were otherwise indistinguishable from other variant cells. This is a surprising result, since, in general, approximately 90% of patients with NPC possess defects in NPC1. Our findings should be useful for the detection of NPC variants and also may provide significant new insight regarding NPC1 genotype/phenotype correlations.

Alleles↗
PubMed2001

Identification of a 55-bp deletion in the glucocerebrosidase gene in Gaucher disease: phenotypic presentation and implications for mutation detection assays.

A 55-bp deletion in exon 9 of the glucocerebrosidase gene was identified in a 28-year-old male affected with Gaucher disease. The diagnosis was established during an evaluation for mild pancytopenia and was confirmed by bone marrow histology and biochemical studies. The patient is of German ancestry. Initial DNA testing indicated homozygosity for the N370S mutation. However, subsequent testing of the patient's parents suggested that the patient and his mother carried a null allele by our assay for N370S. Further molecular studies identified a 55-bp deletion in exon 9 of the glucocerebrosidase gene (g.6767_6822del55). This deletion has been previously reported in a patient with severe Gaucher disease (1), and is present in the glucocerebrosidase pseudogene. In the previously reported case, initial DNA testing also suggested the genotype N370S/N370S, but further mutation studies were undertaken because clinical severity was greater than expected for that genotype. In contrast, our patient has an unusually mild clinical course. Thus, clinical severity cannot be reliably used to determine when to test for the presence of the 55-bp deletion. While the 55-bp deletion is not reported to be common, its actual frequency may be underestimated since it eludes detection by many standard clinical assays for Gaucher disease. This report points out the need to consider this deletion mutation which may cause erroneous interpretation of results in existing assays for the common mutations N370S and L444P. Furthermore, the importance of recommending parental analysis for individuals who test homozygous for autosomal mutations is highlighted.

Adult↗
PubMed2001

A search for germline APC mutations in early onset colorectal cancer or familial colorectal cancer with normal DNA mismatch repair.

Twenty percent of colorectal cancers (CRCs) arise in people who have a family history of CRC in at least one other relative. Although a fraction of these CRCs are explained by two well-described autosomal dominant syndromes-5% by hereditary nonpolyposis colorectal cancer (HNPCC) and 1% by familial adenomatous polyposis (FAP)-the cause of the remaining 14% of familial aggregates of CRC is unknown. Many cases of HNPCC are due to germline mutations in DNA mismatch repair genes, leading to the tumor phenotype of microsatellite instability (MSI), and most cases of FAP are caused by germline APC mutations. To date, non-FAP familial CRC aggregates have not been evaluated for germline APC mutations. In this study, we examined the involvement of germline APC mutations in 79 individuals with CRC who had early-age onset of their cancer (age < 50 years) and/or a family history of CRC. Cases with FAP or HNPCC due to defective mismatch repair were excluded from the study. Using conformation-sensitive gel electrophoresis and the protein truncation test as the screening methods, no functionally significant germline mutations were detected for any of the cases. An apparently silent polymorphism resulting in a 1-bp alteration of A --> G (proline --> proline) in exon 4 was observed. Additionally, four intervening sequence (IVS) alterations were detected: IVS2-53t-->c in 3 cases; IVS4-17ins T in 3 cases; IVS5+32t-->c in 16 cases; and IVS5+33g-->a in 1 case. All appeared to be polymorphisms present in similar proportions in an average-risk population. We conclude that germline APC mutations do not account for familial MSS (stable microsatellite) CRC associated with few synchronous polyps.

Adult↗
PubMed2000

Frequency and clinical significance of the S1235R mutation in the cystic fibrosis transmembrane conductance regulator gene: results from a collaborative study.

More than 900 mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene have been reported to the cystic fibrosis (CF) consortium. A missense mutation, S1235R, was originally reported in a CF patient with a second mutation (G628R) on the same chromosome. The clinical significance of S1235R was not clear. S1235R is not among the commonly reported mutations, and it is not routinely screened for in most laboratories. However, we have detected the S1235R allele at a frequency that is significantly higher than that of many other CF mutations. Among more than 3,000 patients tested for either a possible diagnosis of CF or to determine CF carrier status, we identified 51 patients heterozygous for S1235R. No patients were homozygous for S1235R. Five patients were compound heterozygotes for a second CFTR mutation: two cases (one family) were N1303K/S1235R and three unrelated cases were deltaF508/S1235R. Our data suggest that S1235R, when combined with a second CF mutation, may be pathogenic, although phenotypic manifestations appear to be variable. The possibility that this represents a rare polymorphism cannot be discounted completely. Genetic counseling is difficult when S1235R is identified, even in the presence of a second known mutation, especially in prenatal cases.

Adolescent↗
PubMed2000

Late-onset SCA2: 33 CAG repeats are sufficient to cause disease.

SCA-2 is an autosomal dominant inherited disorder characterized by ataxia, slow saccades, and hyporeflexia. The authors evaluated a patient with a mild balance problem with a SCA-2 allele sized at 33 CAG repeats. The authors then ascertained her 91 year-old mother, who showed disease onset at age 86 with an SCA-2 allele of identical size. Their study indicates that 33 CAG repeats can be pathogenic at the SCA-2 locus, though such an allele may produce an extremely late onset and gradual rate of disease progression.

Aged↗
PubMed2000

Converting visual acuity to utilities.

BACKGROUND: Utility theory can be used to quantify dysfunction associated with various diseases and thus can represent a "hard" measure of quality of life. By determining utility values, one can compare the quality of life of patients with ocular disease to that of patients with non-ophthalmic problems. We performed a study to determine whether utility values from patients with ocular disease are associated with clinical variables, including visual acuity in the better-seeing eye, and to develop a mathematical method for converting visual acuity to utility value, if there is an association between the two. METHODS: Cross-sectional study. A total of 239 patients from a tertiary care retinal practice with various ocular conditions, including macular degeneration, cataract, glaucoma and diabetic retinopathy, were interviewed under standardized conditions to determine their utility values by the time trade-off technique. Visual acuity, duration of visual loss and number of concomitant conditions were also determined. Multiple linear regression was performed to determine which variables were associated with utility values. RESULTS: The mean acuity in the better-seeing eye was 0.479 (near 20/40 vision). The mean utility value was 0.72. Accordingly, the average patient in our series was willing to trade 2.8 of every 10 remaining years of life to obtain perfect vision in both eyes. Utility value was significantly associated with visual acuity in the better-seeing eye (F = 69.1, p < 0.001). Other variables were not significantly associated with utility value. The association with duration of visual loss approached statistical significance (p = 0.075). Utility values (U) for patients with ocular disease can be derived from the following formula: U = (0.374)(visual acuity in better-seeing eye) + 0.514. INTERPRETATION: Utility values from patients with ocular disease were strongly associated with visual acuity and could be estimated mathematically.

Aged↗
PubMed2000

Null alleles at the Huntington disease locus: implications for diagnostics and CAG repeat instability.

PCR amplification of the CAG repeat in exon 1 of the IT15 gene is routinely undertaken to confirm a clinical diagnosis of Huntington disease (HD) and to provide predictive testing for at-risk relatives of affected individuals. Our studies have detected null alleles on the chromosome carrying the expanded repeat in three of 91 apparently unrelated HD families. Sequence analysis of these alleles has revealed the same mutation event, leading to the juxtaposition of uninterrupted CAG and CCG repeats. These data suggest that a mutation-prone region exists in the IT15 gene bounded by the CAG and CCG repeats and that caution should be exercised in designing primers that anneal to the region bounded by these repeats. Two of the HD families segregated null alleles with expanded uninterrupted CAG repeats at the lower end of the zone of reduced penetrance. The expanded repeats are meiotically unstable in these families, although this instability is within a small range of repeat lengths. The haplotypes of the disease-causing chromosomes in these two families differ, only one of which is similar to that reported previously as being specific for new HD mutations. Finally, no apparent mitotic instability of the uninterrupted CAG repeat was observed in the brain of one of the HD individuals.

Aged↗
PubMed2000

Could malaria return to Britain?

With predicted global warming, the mosquito fauna of Britain is certain to change. How will this effect our native Anopheles mosquitoes and the development of malarial parasites within them? Will exotic species become established, and act as more effective vectors of malaria?

Animals↗
PubMed1999

Mannose-binding lectin (MBL) deficiency. Variant alleles in a midwestern population of the United States.

OBJECTIVES: To describe a method for the genotype analysis of mutations in the gene encoding mannose binding lectin (MBL), study the incidence of MBL gene mutations in a population of the Midwest of the United States, and compare it with previous reports in other populations. The objective of this report is also an extensive review of the literature to analyze the importance of MBL deficiency in human disease. DATA SOURCES: Blood samples were obtained from the blood bank of the Mayo Clinic. They represented a population of blood donors living in the Midwest of the United States. A review of the literature was performed by selection of articles from Medline database. STUDY SELECTION: Blood samples, 148, were randomly selected from a pool of blood donors. They included both females and males. Blood donors had been previously screened by a questionnaire and were found to be generally healthy. For the literature review, articles containing original data on MBL in humans were selected. RESULTS: Forty-five (30.4%) of the analyzed blood donors carried one variant allele, while 8 donors (5.4%) showed homozygosity or compound heterozygosity for MBL gene mutations. Allele frequency for the different MBL variants is provided. Our results are similar to those reported for the Danish population. Literature review provides evidence for a significant role of MBL deficiency in the innate immunity. The incidence of MBL mutations is higher among patients with recurrent infections and autoimmune disorders. CONCLUSIONS: Mannose binding lectin deficiency has a definite role in the pathogenesis of primary immunodeficiency in humans and screening patients with recurrent infections and autoimmunity might be beneficial. The significance of MBL deficiency among apparently healthy blood donors remains to be determined.

Adult↗
PubMed1999

Immunogenicity of P/Q-type calcium channel in small cell lung cancer: investigation of alpha1 subunit polyglutamine expansion.

The ectopic expression of neuronal P/Q-type voltage-gated calcium channels in small cell lung carcinoma (SCLC) is thought to induce antisynaptic autoimmunity in the paraneoplastic Lambert-Eaton myasthenic syndrome. The gene CACNL1A4, encoding the principal (alpha1A) subunit of this calcium channel, is mutated in several inherited neurological disorders. One of these disorders (spinocerebellar ataxia, type 6, or SCA-6) involves the expansion of a trinucleotide (CAG) repeat unit. We hypothesized that a somatic CAG repeat instability of this gene in neoplastic cells might generate a non-self epitope capable of initiating autoimmunity to P/Q-type calcium channels. We therefore analyzed the CACNL1A4 gene in SCLC lines established from metastases derived from seven individual patients (four associated with Lambert-Eaton myasthenic syndrome, one associated with myasthenia gravis, and two not associated with neurological autoimmunity). We compared their CAG repeat numbers (determined by polymerase chain reaction (PCR) amplification followed by separation of products on a 6% polyacrylamide/8M urea gel) to published norms and to DNA from a patient with SCA-6. The number of CAG repeats in SCLC DNA fell within a normal range whether or not the neoplasm was complicated by neurological autoimmunity. Therefore, it is unlikely that somatically unstable CAG repeat units in the gene encoding the P/Q-type voltage-gated calcium channel account for this tumor protein's immunogenicity in the Lambert-Eaton myasthenic syndrome.

Autoimmunity↗
PubMed1999

Molecular diagnostics on microfabricated electrophoretic devices: from slab gel- to capillary- to microchip-based assays for T- and B-cell lymphoproliferative disorders.

BACKGROUND: Current methods for molecular-based diagnosis of disease rely heavily on modern molecular biology techniques for interrogating the genome for aberrant DNA sequences. These techniques typically include amplification of the target DNA sequences followed by separation of the amplified fragments by slab gel electrophoresis. As a result of the labor-intensive, time-consuming nature of slab gel electrophoresis, alternative electrophoretic formats have been developed in the form of capillary electrophoresis and, more recently, multichannel microchip electrophoresis. METHODS: Capillary electrophoresis was explored as an alternative to slab gel electrophoresis for the analysis of PCR-amplified products indicative of T- and B-cell malignancies as a means of defining the elements for silica microchip-based diagnosis. Capillary-based separations were replicated on electrophoretic microchips. RESULTS: The microchip-based electrophoretic separation effectively resolved PCR-amplified fragments from the variable region of the T-cell receptor-gamma gene (150-250 bp range) and the immunoglobulin heavy chain gene (80-140 bp range), yielding diagnostically relevant information regarding the presence of clonal DNA populations. Although hydroxyethylcellulose provided adequate separation power, the need for a coated microchannel for effective resolution necessitated additional preparative steps. In addition, preliminary data are shown indicating that polyvinylpyrrolidone may provide an adequate matrix without the need for microchannel coating. CONCLUSIONS: Separation of B- and T-cell gene rearrangement PCR products on microchips provides diagnostic information in dramatically reduced time (160 s vs 2.5 h) with no loss of diagnostic capacity when compared with current methodologies. As illustrated, this technology and methodology holds great potential for extrapolation to the abundance of similar molecular biology-based techniques.

DNA, Neoplasm↗
PubMed1998

Spinocerebellar ataxia type 2 (SCA 2) in an infant with extreme CAG repeat expansion.

Autosomal dominant cerebellar ataxias are a heterogeneous group of neurodegenerative disorders that generally present in adulthood. Spinocerebellar ataxia type 2 typically presents with progressive cerebellar symptoms, slow ocular saccades, and peripheral neuropathy. The onset of symptoms is usually between 20 and 40 years. We describe an infant who presented with neonatal hypotonia, developmental delay, and dysphagia. Ocular findings of retinitis pigmentosa were noted at 10 months. Her father had mild spinocerebellar ataxia first noted at age 22 years. Molecular studies of the SCA2 gene showed a CAG expansion of 43 repeats in the father and an extreme CAG repeat expansion of more than 200 in the baby. Our report expands the known phenotype and genotype of SCA2. Testing for dominant ataxias should be included in the evaluation of infants with nonspecific progressive neurologic symptoms and retinitis pigmentosa, especially in cases with a positive family history for spinocerebellar ataxia.

Ataxins↗
PubMed1998

Clostridium difficile-associated diarrhea in acute and long-term care facilities.

This report presents an overview of the epidemiology, diagnosis, complications, and treatment of Clostridium difficile-associated diarrhea in acute and long-term care facilities. More studies are needed to understand the epidemiology of this disease in long-term care facilities, to identify the risk factors for its recurrence, and to evaluate new treatment modalities.

Anti-Bacterial Agents↗
PubMed1996

Segregation of the fragile X mutation from a male with a full mutation: unusual somatic instability in the FMR-1 locus.

Fragile X syndrome is associated with an unstable CGG-repeat in the FMR-1 gene. There are few reports of affected males transmitting the FMR-1 gene to offspring. We report on a family in which the propositus and his twin sister each had a full mutation with abnormal methylation. Their mother had an FMR-1 allele in the normal range and a large premutation, with normal methylation. The maternal grandmother had two normal FMR-1 alleles. The maternal grandfather had an unusual somatic FMR-1 pattern, with allele size ranging from premutation to full mutation. No allele was detectable by PCR analysis. Multiple Southern blot analyses identified a hybridization pattern that originated at a distinct premutation band and extended into the full mutation range. Methylation studies revealed a mosaic pattern with both unmethylated premutations and methylated full mutations. This individual declined formal evaluation but did not finish high school and has difficulty in reading and writing. The size of the premutation FMR-1 allele passed to his daughter is larger than his most prominent premutation allele. This is most likely due to gonadal mosaicism similar to that in his peripheral lymphocytes. Alternatively, this expansion event may have occurred during his daughter's early embryonic development and this large premutation allele is mitotically unstable. This pattern of FMR-1 alleles in a presumably mildly affected male is highly unusual. These findings are consistent with the absence of transmission of a full fragile X mutation through an expressing male. Studies of tissue specific FMR-1 allele expansion and FMR-1 protein expression on this individual should help to determine the correlation of the molecular findings with the phenotypic effects.

Alleles↗