Search PubMed⌕ Search

Biomedical subjects

E de Graaff

Publications and source records attributed to E de Graaff.

31 records · Page 2Linked to original sources
PubMed1993

Alternative splicing in the fragile X gene FMR1.

The FMR1 gene, associated with fragile X syndrome, has recently been cloned and the sequence of partial cDNA clones is known. We have determined additional cDNA sequences both at the 5' and 3' end. We have characterized the expressed gene by means of RT-PCR in various tissues and have found that alternative splicing takes place in the FMR1 gene, which does not seem to be tissue specific. When the different alternative splicing events are combined, 12 distinct mRNA products could result from FMR1 expression in each tested tissue. In all these transcripts the open reading frame is maintained until the same stop codon. At the 3' end alternative use of polyadenylation signals is found. The alternative splicing allows functional diversity of the FMR-1 gene. Whether all the possible proteins will be synthesized and whether they will be functionally active has to be determined.

Alternative Splicing↗
PubMed1993

Mental status and fragile X expression in relation to FMR-1 gene mutation.

The fragile X mental retardation syndrome is caused by unstable expansion of a CGG repeat in the FMR-1 gene. Clinical expression is associated with a large expansion of the CGG repeat. The mutation in the FMR-1 gene and the cytogenetic expression of the fragile site at Xq27.3 have been studied in 52 fragile X male patients. The percentage of the cytogenetic expression of the fragile site at Xq27.3 positively correlates with the mean size of the full mutation in the FMR-1 gene (p < 0.0001) irrespective of the presence of additional premutation alleles. We noted a less frequent occurrence of additional premutation alleles in adult patients compared with juveniles, suggesting a continued mitotic instability in life. Additionally, the level of mental retardation has been ascertained in 35 patients using the Stanford-Binet or Terman-Merrill test of general intelligence. The presence of a full mutation in the FMR-1 gene seemed decisive for the occurrence of mental impairment in the patient. No correlation is observed between the degree of mental retardation and the size of the full mutation. The degree of mental retardation seemed not to be influenced by the presence of premutation alleles in part of the cells in addition to a full mutation. One patient is described with the 'Prader-Willi-like' subphenotype of the fragile X syndrome, showing a deletion in the FMR-1 gene in a part of his cells in addition to a full mutation.

Adult↗
PubMed1992

Clonal involvement of granulocytes and monocytes, but not of T and B lymphocytes and natural killer cells in patients with myelodysplasia: analysis by X-linked restriction fragment length polymorphisms and polymerase chain reaction of the phosphoglycerate kinase gene.

To determine the clonal nature of hematopoiesis and to assess lineage involvement in patients with myelodysplastic syndromes (MDS), we used restriction fragment length polymorphisms of the X-linked genes phosphoglycerate kinase (PGK1) and hypoxanthine phosphoribosyltransferase (HPRT) and the X-linked probe M27 beta. Eleven female MDS patients heterozygous for at least one of these probes were studied: 3 with refractory anemia (RA), 2 with RA with ringed sideroblasts (RARS), 2 with chronic myelomonocytic leukemia (CMML), and 4 with RA with excess of blasts in transformation (RAEB-t). All exhibited clonal hematopoiesis as determined by Southern analysis of DNA prepared from peripheral blood (PB) and/or bone marrow (BM) cells. In three of the six patients heterozygous for the PGK1 gene, purified cell suspensions of polymorphonuclear cells (PMN), monocytes, lymphocytes, and/or T cells prepared from PB were tested. In addition, five of these patients were analyzed by a polymerase chain reaction (PCR)-based procedure as described recently. This method was slightly adapted to facilitate the analysis of cell lysates of fluorescence-activated cell sorted (FACS) monocytes, T and B lymphocytes, and natural killer (NK) cells. The outcome of Southern and PCR analysis was concordant, showing that PMN and monocytes were clonally derived, whereas circulating T and B lymphocytes and NK cells exhibited random X-chromosome inactivation compatible with a polyclonal pattern. To address the question of whether T cells are derived from unaffected progenitor cells or that their origin had antedated the onset of MDS, naive and memory T cells were analyzed separately. Both subsets showed a polyclonal pattern. However, in one patient analysis of constitutive DNA suggested a skewed methylation, and the presence of clonal lymphocytes against a background of polyclonal lymphoid cells cannot be ruled out in this patient. PCR analysis of PB and BM cells showed a nonrandom, unilateral pattern of X-inactivation, compatible with a mixture of clonally (myeloid) and polyclonally (lymphoid) derived cells. In conclusion, in some patients, MDS represents a disorder with clonal hematopoiesis restricted to cells of myeloid origin, whereas a random X-inactivation pattern is found in lymphoid cells.

Adult↗
PubMed1991

Identification of a point mutation in the human lysosomal alpha-glucosidase gene causing infantile glycogenosis type II.

Two patients in a consanguineous Indian family with infantile glycogenosis type II were found to have a G to A transition in exon 11 of the human lysosomal alpha-glucosidase gene. Both patients were homozygous and both parents were heterozygous for the mutant allele. The mutation causes a Glu to Lys substitution at amino acid position 521, just three amino acids downstream from the catalytic site at Asp-518. The mutation was introduced in wild type lysosomal alpha-glucosidase cDNA and the mutant construct was expressed in vitro and in vivo. The Glu to Lys substitution is proven to account for the abnormal physical properties of the patients lysosomal alpha-glucosidase precursor and to prevent the formation of catalytically active enzyme. In homozygous form it leads to the severe infantile phenotype of glycogenosis type II.

Alleles↗
PubMed1989

A test of medical problem-solving scored by nurses and doctors: the handicap of expertise.

There is evidence that nurses fulfil the requirements of objective judgement better than doctors. Simulation of Initial Medical Problem-Solving (SIMP), a paper-and-pencil test for the assessment of medical problem-solving, consists of case histories, followed by an open-ended question. The scoring of open-ended questions is time-consuming and adds subjective bias to measurement error. In order to reduce scoring error, answers on SIMP are scored by means of scoring models in the form of check-lists with descriptions of elements of a correct answer. The reliability of the scoring was analysed in a study, with six nurses rating 500 answers. The overall interrater reliability was high, expressed by an intra-class correlation of 0.83. Selection of raters, and improvement of the scoring models, could increase the interrater reliability even further. In addition to the scoring by the nurses part of the material was scored again by two experienced doctors. The reliability of the scoring method on the whole was confirmed. Nevertheless, some evidence was found of misinterpretation of the scoring models by the nurses. Analysis at the item level revealed several instances in which both doctors agreed on a score for an element in an answer and all the nurses agreed on the opposite score. On the other hand, however, the two doctors were less consistent between themselves than the nurses. The disagreement between the doctors seems to be a consequence of differences in their own medical judgement of the case in question. The impact of the mistakes that are made by the nurses is much smaller than the loss of reliability caused by the inconsistency among the doctors.

Educational Measurement↗
PubMed1987

Validation of a new measure of clinical problem-solving.

A review of the literature on the assessment of medical problem-solving by means of written tests reveals serious short-comings. Most important is the low correlation repeatedly found among cases, which suggests the inability of the measures to assess a general problem-solving ability. The literature further suggests that instruments should focus on the brief period of time after the first encounter of a clinical problem and warns against the effects of cueing. Based on these considerations a new measure for the assessment of medical problem-solving was developed. This test, called Simulation of Initial Medical Problem-Solving (SIMP), consists of a number of short case histories, followed by an open-ended question. Reliability analysed by means of generalizability theory proved satisfactory and concurrent validity was established by a significant correlation with a global judgement of performance in a simulated patient encounter. The moderate correlation between cases is interpreted as an acceptable correlation among test items and leads to the conclusion that a reliable and valid test of clinical problem-solving should consist of a substantial number of different cases.

Clinical Competence↗
PubMedDate not supplied

Responses of experimental rat tumours and a mouse colon tumour to flavone acetic acid.

The toxicity in rats and mice and the responses of 5 rat lung tumours, a rat rhabdomyosarcoma and a mouse colon tumour to flavone acetic acid, FAA, were studied. The LD50 values of FAA in WAG/Rij and BN rats were about 350 and 525 mg/kg respectively, independent of whether the animals were tumour bearing or not. In contrast, the LD50 value of tumour bearing BCBA mice was 50 percent of that of non-tumour bearing mice. Neither tumour volume regression nor growth delay were observed in the rat tumours growing in syngeneic rats or in nude mice, in contrast to the response of colon 38 tumours in mice. Light microscopy revealed massive tumour necrosis in the mouse tumour while no significant changes were observed in the rat tumours.

Animals↗
PubMedDate not supplied

FMR1 premutation allele (CGG)81 is stable in mice.

Fragile X syndrome is caused by an expansion of the CGG repeat present in the 5' UTR of the FMR1 gene. A lot has been elucidated about the genetics of the disease, but not much is known about the mechanisms involved in repeat instability. Transgenic animals with a premutation allele [(CGG)11AGG(CGG)60CAG(CGG)8] in the human FMR1 promoter were generated to study the inheritance of this repeat in mice. Three independent lines, B6, B7 and B29, in total 263 transgenic animals, were tested for repeat instability. In all meiosis and mitosis tested, the repeat inherited stably. This suggests that other factors might be important in repeat (in)stability.

Alleles↗