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Biomedical subjects

D Ledbetter

Publications and source records attributed to D Ledbetter.

16 recordsLinked to original sources
PubMed1999

The effect of the duration and structure of a surgery clerkship on student performance.

The emphasis on a generalist professional education has led to shortening and restructuring of the surgery clerkship in the curricula of many medical schools. Little data exist regarding the effect of these changes on student performance. Therefore, we examined the effect of the length, timing, and content of the third year surgery rotation on several clerkship and postclerkship performance measures of 487 students from July 1994 to July 1998. In addition, students' perceptions regarding their ability to understand surgical disease topics were surveyed. The 8-week clerkship (n = 232) was associated with higher NMBE surgery test scores (510.5 +/- 6.3 versus 457.4 +/- 10.0, P < 0.05) resulting in higher final clerkship grades (5.15 +/- 0.04 versus 4.87 +/- 0.03, P < 0.05). Although clerkship length had no significant effect on USMLE step 2 total or surgery subsection scores, the longer clerkship was associated with higher total (70.6 +/- 0.37 versus 68. 8 +/- 0.50, P < 0.05) and abdominal pain station (81.87 +/- 0.71 versus 79.54 +/- 0.73, P < 0.05) OCSE scores. Students rotating on surgery during the second half of third year (n = 233) had higher NMBE surgery test scores (513.1 +/- 8.9 versus 460.5 +/- 11.2, P < 0. 05) and final grades (5.17 +/- 0.03 versus 4.81 +/- 0.04, P < 0.05). Although the timing of the surgery clerkship did not significantly affect total OSCE scores, students who rotated on surgery in the second half of third year performed significantly better year on the abdominal pain OSCE station (80.47 +/- 0.92 versus 76.49 +/- 1.27, P < 0.05). Students who rotated on general surgery (n = 298) performed significantly better on the NBME surgery test (525.6 +/- 6.0 versus 459.6 +/- 9.1, P < 0.05), although this did not significantly affect the final grade. Although general versus subspecialty surgery rotation did not significantly affect total OSCE scores, students rotating on general surgery performed significantly better on the abdominal pain OSCE station (81.21 +/- 0.91 versus 78.17 +/- 0.32, P < 0.05). The length, timing, and content of the third year surgery rotation had no significant effect on performance on the oral examination. Students who had a 6-week clerkship and students who lacked exposure to general surgery felt their surgery rotation failed to prepare them to understand a number of surgical topics as well as students who had an 8-week clerkship or students who rotated on general surgery. The length, timing, and content of the surgery clerkship affect some clerkship performance measures and student perceptions of their understanding of surgical disease topics. While cognitive differences related to clerkship length are no longer detectable at the end of the third year of medical school, differences related to the acquisition of some clinical skills persist after the surgery clerkship.

Achievement↗
PubMed1999

Endoscopic evaluation of the esophagus in infants and children immediately following intraoperative use of transesophageal echocardiography.

OBJECTIVE: Intraoperative transesophageal echocardiography (TEE) has evolved as an essential technique for use during pediatric cardiac surgery; however, few studies have evaluated the safety of TEE in children. This series reports endoscopic examination of the esophagus following intraoperative TEE in pediatric patients. METHODS: Fifty children undergoing congenital heart surgery underwent flexible esophagoscopy that was performed after completion of their heart surgery and after the removal of the transesophageal echo probe. The patients' ages ranged from 4 days to 10 years old, and their weight ranged from 3.0 to 39.8 kg, with a mean weight of 12.6 kg. RESULTS: Thirty-two of 50 patients (64%) had abnormal results shown on esophageal examinations; this occurred more frequently in the subset of patients weighing < 9 kg. No long-term feeding or swallowing difficulties were noted in any of the 48 patients who survived. CONCLUSIONS: Intraoperative TEE in infants and children frequently caused mild mucosal injury. Care must be exercised in the insertion and manipulation of the probes.

Cardiac Surgical Procedures↗
PubMed1998

Chromosome 20 ring: a chromosomal disorder associated with a particular electroclinical pattern.

PURPOSE: The chromosome 20 ring [r(20)] is a rare chromosomal disorder without clear phenotypical markers. We describe the electroclinical pattern in a group of patients with r(20). METHODS: We observed 3 patients (a boy, patient 1; his mother, patient 2; and an unrelated man, patient 3), performing prolonged video-EEG and cytogenetic studies and fluorescent in situ hybridization (FISH) with chromosome-specific telomeric probes. RESULTS: All 3 patients had a very similar abnormal electroclinical pattern characterized by long bursts or trains of rhythmic theta waves, which were sharply contoured or had a notched appearance (with no detectable clinical correlate), and generalized spike waves (SW) associated with seizures of probable frontotemporal origin (SFT). In all 3 patients, the cytogenetic analysis of T lymphocytes showed mosaicism with a normal cell line and a second cell line with a chromosome 20, although the latter was little represented in patients 2 and 3. A few cells with a single chromosome 20 were also found. The same cytogenetic findings were confirmed in the lymphoblastoid cell line of patient 1 and in the fibroblasts of patient 3. FISH with chromosome-specific telomeric probes and TTAGGG sequences demonstrated the integrity of the ring chromosomes. CONCLUSIONS: The clinical picture of these patients appears to be related to the instability of the r(20)-generating cells monosomic for chromosome 20 and is thus haploinsufficient for a gene. In these patients, the electroclinical pattern of theta waves (probably unrelated to epilepsy) and the SW and SFT, even with mild mental retardation (MR) or no MR and without dysmorphic features, suggest that the r(20) syndrome may be present.

Adolescent↗
PubMed1996

Fine mapping of the cystinosis gene using an integrated genetic and physical map of a region within human chromosome band 17p13.

The cystinosis gene has been reported to reside in a 3.1 cM region of chromosome 17p13 flanked by markers D17S1828 and D17S1798. We created a yeast artificial chromosome (YAC) contig between these markers and report here an integrated genetic and physical map which will aid in the identification of other genes in this area. Using one pertinent YAC clone, 898A10, we identified new polymorphic markers in the cystinosis gene region. One such marker, D17S2167, was localized by radiation hybrid analysis to within 10.2 cR8000 of D17S1828. Haplotype analysis in two separate informative families revealed recombination events which placed the cystinosis gene between markers D17S1828 and D17S2167, an area estimated to be 187-510 kb in size. This dramatic narrowing of the cystinosis gene region permits the creation of a P1 or cosmid contig across the area of interest. The ultimate cloning of the cystinosis gene should eventually reveal how a functional lysosomal transport protein is synthesized, targetted, processed, and integrated into the lysosomal membrane.

Base Sequence↗
PubMed1993

Molecular definition of the Prader-Willi syndrome chromosome region and orientation of the SNRPN gene.

The Prader-Willi syndrome and the Angelman syndrome are caused by the loss of function of distinct but closely linked genes on human chromosome 15. Based on a yeast artificial chromosome restriction map and two key patients we have determined that the shortest region of deletion overlap in the Prader-Willi syndrome comprises 320 kb. The region includes the anonymous DNA marker PW71 (D15S63) and the gene for the small nuclear ribonucleoprotein N (SNRPN). The SNRPN gene maps 130 kb distal to PW71 and is transcribed from centromere to telomere.

Autoantigens↗
PubMed1992

Foreign bodies within a Meckel's diverticulum.

Although complications of Meckel's diverticula are relatively common, there has not been a reported case, to our knowledge, of foreign bodies impacted within a Meckel's diverticulum. We report herein a case of a 2-year-old child who had two pennies trapped in a Meckel's diverticulum. This case demonstrates that foreign objects in the right lower quadrant that do not progress may be impacted in a Meckel's diverticulum.

Acute Disease↗
PubMed1992

Congenital 21-hydroxylase deficiency as a new deletion mutation. Detection in a proband during subsequent prenatal diagnosis by HLA typing and DNA analysis.

A child with 21-OH-def whose 9 weeks' pregnant mother was referred for prenatal diagnosis was found upon very careful histocompatibility testing to lack expression of any of his father's HLA antigens on his peripheral blood lymphocytes. The possibility of alternative paternity was considered to be extremely unlikely after additional genetic marker tests. The conclusion that the affected child's disease resulted from inheritance of a maternal CYP21B (21-OH) deletion and a de novo deletion in the paternal chromosome 6 segment that includes both the CYP21B (21-OH) and HLA genes was confirmed by subsequent DNA analysis using 21-OH, C4, DPB, and PCH6 probes. The presence of a heterozygous RFLP for DPB, the absence of a deletion for either CYP21B (21-OH) or C4 genes, and the presence of a paternal HLA antigen haplotype on the fetal cells additionally indicated that the fetus lacked the same deletion and could be predicted to be completely normal.

Adrenal Hyperplasia, Congenital↗
PubMed1991

Localization of the cellular retinoic acid binding protein (CRABP) gene relative to the acute promyelocytic leukemia-associated breakpoint on human chromosome 15.

A human genomic fragment comprising the cellular retinoic acid binding protein (CRABP) gene was isolated. By using a panel of somatic cell hybrids, this gene could be assigned to human chromosome 15. Subsequently, a possible involvement of the CRABP gene in translocation (15;17) (q22;q11) positive acute promyelocytic leukemia (APL) was investigated. Although transposition of the CRABP gene could be demonstrated, we did not observe any gross CRABP rearrangement in a series of primary APL patients, nor in the acute myeloblastic leukemia cell line HL-60. Thus, the observed lack of CRABP expression in these leukemic cells may not be caused by disruption of its gene. CRABP maps to the region 15q22-qter.

Blotting, Northern↗
PubMed1990

New insights into idiopathic infantile arterial calcinosis. Three patient reports.

We describe the occurrence of idiopathic infantile arterial calcinosis in three newborn siblings. Unusual features in this disease include ultrasonographic prenatal diagnosis in the second two siblings and ultrastructural studies of the third patient that might shed light on the pathophysiologic characteristics of this disease. Ruthenium-red staining for proteoglycans showed a clearly abnormal structure for the granules in areas of calcification. The granules appeared disorganized, with loss of their normal honeycomb interconnections. They also varied in size and density. In addition, matrix vesicles that might serve as nucleation sites for crystalline calcium phosphate were observed in zones of calcification.

Adult↗
PubMed1990

Molecular characterization of human and bovine rod photoreceptor cGMP phosphodiesterase alpha-subunit and chromosomal localization of the human gene.

Defects in proteins that function in photoreceptor signal transduction are prime suspects as causes of some human hereditary retinal degenerations. We have characterized cDNA clones encoding the alpha-subunit of human and bovine rod cell cGMP phosphodiesterase a key phototransduction enzyme. Clones from both species contain an open reading frame capable of coding for an approximately 100-kDa polypeptide of 859 amino acids, 94% of which are identical. Two or more transcripts were detected in both human and bovine retinal poly(A)+ RNA preparations, although the human transcripts ranging from 5.3 to 4.9 kb are significantly larger than the two bovine transcripts of 4.6 and 4.0 kb. The bovine and human genes appear to exist in single copy, with the bovine gene spanning more than 140 kb of genomic DNA. Somatic cell hybrids were used to map the human gene to the long arm of chromosome 5 (5q31.2----q34). Finally, the use of the candidate gene approach in the study of hereditary retinal dystrophies is discussed.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1987

Familial Prader-Willi syndrome with apparently normal chromosomes.

We report on 4 sibs (2F, 2M) with Prader-Willi syndrome (PWS). Diagnosis was made clinically on the basis of history, behavior, and physical findings in 3 of the sibs. The other child had died at age 10 months with a history and clinical findings typical of first phase of PWS. Results of chromosome studies on the parents and surviving sibs were normal. The implications of this unusual familial occurrence for our understanding of PWS are discussed.

Adult↗
PubMedDate not supplied

Mapping of a cerebellar degeneration related protein and DXS304 around the fragile site.

We have localized the gene encoding a cerebellar degeneration related (CDR) protein to a region proximal to the fragile site close to DXS98 and DXS105. This gene is polymorphic with the enzyme RsaI and therefore also provides a new genetic marker in this region. We have refined the localization of the locus DXS304 distal to the breakpoint in a patient suffering from Hunter disease. This confirms the localization of DXS304 distal to the fragile site previously suggested by linkage studies and localizes the fragile X mutation to a relatively small region between the Hunter breakpoint and the breakpoint in another hybrid B17.

Base Sequence↗
PubMedDate not supplied

MRX8: an X-linked mental retardation condition with linkage to Xq21.

A family in which 6 males have X-linked mental retardation has been studied with polymorphic DNA probes. The males differ from unaffected males only in impaired intellect and in smaller head size. The gene that causes mental retardation in the family appears to be located in band Xq21 on the basis of linkage with 3 markers: DXS250, DXS345 and DXS3 (theta max = 0.00; Zmax = 1.6). A multipoint lod score of 2.36 was obtain with no recombination relative to DXS326 in Xq21. This family is considered to have nonspecific X-linked mental retardation and has been given the designation MRX8.

Adult↗
PubMedDate not supplied

Spastic paraplegia with iron deposits in the basal ganglia: a new X-linked mental retardation syndrome.

We report on a family with X-linked mental retardation (XLMR) and severe spastic paraplegia. Appearance is normal but there is severe involvement of the lower limbs (affected relatives never walked), with minimal involvement of the upper limbs and unusual MRI findings including macrogyria, white matter hypoplasia, lack of myelination and a markedly increased paramagnetic signal suggestive of iron deposition. Linkage studies documented possible linkage, with no recombination, between the disease locus and DXS424. A 7-point linkage analysis yielded a maximum LOD score of 1.9, (theta = 0.00) for three loci spanning Xq22-q25. The combination of the unusual clinical and MRI findings and the tentative localization to a region different than other XLMR syndromes with spastic paraplegia, provide good evidence that this is a new XLMR syndrome.

Adult↗