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Biomedical subjects

G W Stewart

Publications and source records attributed to G W Stewart.

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

Temperature effects on cation transport in hereditary stomatocytosis and allied disorders.

The conditions known as 'hereditary stomatocytosis and allied syndromes' comprise a group of dominantly inherited human haemolytic anaemias characterized by a plasma membrane 'leak' to the univalent cations Na and K, an example of a small but growing group of diseases where pathology can be directly attributed to abnormal membrane transport. A number of case reports in the different variants have alluded to temperature-related phenomena, including loss of K on storage at room temperature (giving 'pseudohyperkalaemia') and lysis of cells when stored in the cold ('cryohydrocytosis'). This review collects together published studies of these temperature effects, which show very major differences in the 'leak' K transport. Two main variations on normal emerge: a 'shallow slope' type, in which the flux shows an abnormally low dependence on temperature in the range 37-20 degrees C, and 'high minimum', in which the minimum in this flux, which occurs in normal cells at 8 degrees C, is shifted up to 23 degrees C. These temperature studies provide a powerful method for phenotypic characterization.

Anemia, Hemolytic, Congenital↗
PubMed1999

The hereditary stomatocytoses and allied disorders: congenital disorders of erythrocyte membrane permeability to Na and K.

The hereditary stomatocytoses and allied disorders are a set of dominantly inherited haemolytic anaemias in which the plasma membrane of the red cell 'leaks' sodium and potassium. There are about 10 different forms of these conditions, ranging from a moderately severe haemolytic anaemia to minor conditions in which the haematology is essentially normal, but where the patients present with pseudohyperkalaemia, due to leakage of K from the red cells on cooling to room temperature. Frequently misdiagnosed as atypical hereditary spherocytosis, these conditions can show marked thrombotic complications after splenectomy, which should be avoided. Laboratory studies of these conditions have drawn attention to a 32 kDa membrane protein, stomatin, which seems to act as a regulator of Na and K transport in human and animal tissues generally, but mutations in this gene do not cause these diseases. Genetic mapping in some kindreds, but not all, points to a mutation locus on chromosome 16.

Anemia, Hemolytic, Congenital↗
PubMed1998

Utilization of an 86 bp exon generates a novel adducin isoform (beta 4) lacking the MARCKS homology domain.

A novel isoform of beta-adducin has been amplified and characterized from a human bone marrow cDNA library (GenBank #U43959). This isoform arises from the insertion of an 86 bp alternatively spliced and previously unrecognized exon (now termed exon 15) within codon 581 of the human red blood cell beta-adducin sequence. This results in an insertion of 28 novel amino acids. The remainder of the red cell beta-adducin mRNA is then translated in a different reading frame, adding an additional 35 novel amino acids prior to the stop codon. This new isoform, thus, replaces beta 1-adducin sequence after residue 580 with a total of 63 new amino acids. Sequences from genomic clones of the human beta-adducin gene show that this alternate exon is flanked by splice consensus sequences and is appropriately located in the genomic map between exons encoding up-stream and down-stream sequences, thus defining a new exon. The COOH-terminus of this new isoform, which we designate beta 4, lacks a 22 amino acid lysine-rich sequence common to both the human red cell alpha- and beta-adducin subunits and homologous to a highly conserved region in MARCKS, a filamentous actin-cross linking protein regulated by protein kinase C and calcium/calmodulin. beta 4-adducin preserves a previously identified calmodulin binding domain. PCR analysis indicates that this new beta-adducin isoform is expressed in fetal brain and liver, bone marrow, and NT-2 (neuroepithelial) cells, but is not detected in several other tissues. We anticipate that this new beta 4 isoform of beta-adducin will display unique and tissue-specific functional properties.

Alternative Splicing↗
PubMed1997

Stomatin.

Stomatin is a 31-kDa integral membrane protein, named after the rare human haemolytic anaemia hereditary stomatocytosis. In some cases of this anaemia, in which the red cells leak sodium and potassium ions, this protein is absent from the membrane, immediately suggesting that it has a role in the regulation of ion transport. The protein has a single hydrophobic domain, presumed to be membrane-associated, is phosphorylated, and is widely distributed in animal tissues. Mutations of a homologue in sensory nerve cells of the nematode Caenorhabditis elegans disrupt a neuronal transduction mechanism, in which mechanosensory information is relayed to an ion channel, whose opening initiates an action potential. It could be that this protein is a molecular link in a genetic stretch-sensitive system. Abnormalities of red cell ion transport are well known in human hypertension, but the molecular basis has never been elucidated: this protein and its functional associates, operating in a stretch- or pressure-sensitive complex, might be important.

Animals↗
PubMed1997

High school football-related cervical spinal cord injuries in Louisiana: the athlete's perspective.

Louisiana has one of the highest rates in the nation of cervical spinal cord injuries to high school football players. When the national rate of these injuries is applied to the number of high school participants in Louisiana, we would expect there to be only one catastrophic neck injury every 14 years. Louisiana, however, has averaged 2.3 spinal cord injuries per year for the past seven football seasons. Players who use the top of their helmets to tackle, block, or strike opponents are at greatest risk for these injuries. This study was undertaken to describe the safe tackling knowledge, attitudes, and practices of Louisiana high school football players. We surveyed 596 players from 16 Louisiana high schools. When asked if it was within the rules to tackle anyone by using the top of their helmet, 29% incorrectly answered "yes". Similarly, when asked if they had ever tackled anyone using the top of their helmet, 33% reported that they had. Twenty-eight percent said that they had been taught to use this unsafe method. Of these, 83% said that their coach taught them this dangerous and illegal method. Using the helmet as a battering ram must be discouraged. Education for officials, coaches, and players is needed to improve recognition of improper tackling. Proper training in tackling and blocking is an important means of minimizing the possibility of catastrophic injury.

Adolescent↗
PubMed1997

Evaluation of a program of university placement for spinal cord injured rehabilitation clients in Louisiana.

The Louisiana State Department of Social Services, Rehabilitation Services (LRS) offers a program of financial support for spinal cord injured persons to attend college. We evaluated this program's effectiveness and attempted to identify factors that may predict student success. We examined the LRS case records of all students with documented SCI who had enrolled in the LRS college program before 1988. We compared the proportion of LRS clients who graduated with the proportion of general population students attending the same schools. We measured the association between graduation and factors that may help predict success. Of the 51 LRS clients studied, 25 (49%) graduated from baccalaureate institutions within 6 years. Of Louisiana students-at-large who attended the colleges that housed LRS students, 36% of those graduated within 6 years. The best predictor of success was the American College Test score. All students with a score of 17 or more graduated. A larger proportion of LRS-sponsored students graduated than did students from the general population.

Adult↗
PubMed1996

Thrombo-embolic disease after splenectomy for hereditary stomatocytosis.

Nine cases of hereditary stomatocytosis (HSt) are presented which show documented thrombotic complications after splenectomy. In three cases, patients became severely ill with pulmonary hypertension and a fourth developed portal hypertension. One unsplenectomized affected adult relative had suspected but unconfirmed thrombotic pathology; the six other affected unsplenectomized adults did not. Since splenectomy is of only limited therapeutic benefit in stomatocytosis, it should not be performed without careful consideration. A tendency to iron overload, even without hypertransfusion and irrespective of splenectomy, is evident in many of these patients.

Adult↗
PubMed1995

Sports medicine in physical medicine and rehabilitation residency programs.

Because sports medicine is a rapidly expanding field within many specialties, it is important to gauge how active physiatrists have become in this arena. A nationwide survey of program directors and chief residents of physical medicine and rehabilitation residency programs was conducted to determine such prevalence. For the purposes of this study, sports medicine was defined as the routine care of athletes involved in organized sporting activities at any level of competition. Questionnaires were mailed to program directors and chief residents with response rates of 79.7% each. Overall, correlation of the answers between groups was high. The level of interest of residents was rated at 46%. Data was also obtained regarding research, clinical rotations, lectures, fellowships, association with academic departments of other specialties, and affiliations with professional sports medicine organizations. The actual level of educational opportunities available was much lower than might be expected given the high level of interest expressed. It is reasonable to conclude that more opportunities should exist for education in sports medicine.

Career Choice↗
PubMed1995

Continuities between psychiatric disorders in adolescents and personality disorders in young adults.

OBJECTIVE: Personality disorders are a major mental health problem, but little information about their etiology and natural history is available. This study examined continuities between axis I disorders in adolescents and personality disorders in young adults. METHOD: The authors interviewed 145 young adults (mean age, 19.6 years) who had been diagnosed with a variety of DSM-III emotional and disruptive disorders during adolescence (mean age, 13.7 years). The Personality Disorder Examination was used to establish whether the subjects currently suffered from personality disorders. RESULTS: Subjects who had had disruptive disorders during adolescence showed high rates of all types of personality disorders (40% had a personality disorder at follow-up), while subjects who had had emotional disorders had a lower rate of personality disorders (12%). Men were more likely to have cluster A personality disorders, and women were more likely to have cluster C personality disorders. Disruptive diagnoses were associated with cluster B personality disorders, but emotional disorders did not show an association with cluster C personality disorders. Oppositional disorder did not increase the likelihood of passive-aggressive personality disorder. There was an association between attention deficit disorder with hyperactivity and borderline personality disorder. CONCLUSIONS: The rate of personality disorders was lower among young adults who had had emotional disorders during adolescence than among those who had had disruptive disorders, suggesting either that treatment for emotional disorders is more effective or that the personality psychopathology in these adolescents is not as severe as that in adolescents with disruptive disorders.

Adolescent↗
PubMed1994

Splinting for carpal tunnel syndrome: in search of the optimal angle.

Carpal tunnel syndrome (CTS) is the most common of the compression neuropathies. Several studies have demonstrated the efficacy of wrist splinting in relieving the symptoms of CTS; however, the chosen angle of immobilization has varied. Wick catheter measurements of carpal tunnel pressures suggest that the neural position has less pressure and, therefore, greater potential to provide relief from symptoms. This study is a prospectively gathered, blind trial comparing the symptom relief experienced by wearers of splints immobilized at 20 degrees extension and at neutral. The results indicate that the neutral angle provided superior symptom relief, and that the relief did not often improve between 2 weeks and 2 months of wear. Relief of symptoms was not related to the length of time that the patient had experienced of CTS symptoms. The results also indicate that the results of the electromyography/nerve conduction study (EMG/NCS) do not provide information about the subjects' likely response to splinting.

Carpal Tunnel Syndrome↗
PubMed1994

Paraplegia in a patient with Marfan's syndrome as a result of a thoraco-abdominal aortic aneurysm repair.

Marfan's syndrome is a hereditary disorder involving a deficit in connective tissue collagen. Physical findings include musculoskeletal, ocular, and cardiovascular abnormalities. A 29-year-old man with a history of Marfan's syndrome was admitted to the hospital with back and chest pain secondary to a dissecting aortic aneurysm. He later underwent surgical aortic bypass graft surgery. Postoperatively, he was paraplegic. Our impression was anterior spinal artery syndrome due to prolonged cross-clamping of the aorta during surgical repair. This paper shows the risk of paralysis resulting from surgical repair of an aortic aneurysm as a poorly documented complication of Marfan's syndrome.

Adult↗
PubMed1994

Serum potassium, hydrogen ion and magnesium: neuromuscular regulation by variation of cation concentration in the extracellular fluid?

It is a common clinical observation that changes in serum [K] are frequently associated with changes in serum [H] and/or [Mg]. Thus, hypokalaemia and alkalosis are associated, as are hyperkalaemia and acidosis, and hypokalaemia and hypomagnesaemia. Most investigators would accept that these ions have important roles in the maintenance of neuromuscular excitability. Extracellular potassium exerts its effect by defining the potassium gradient across the cell membrane and therefore the membrane potential in the resting state; magnesium and hydrogen ion 'screen' negative charges on the surface of nerve cells, modulating the local transmembrane potential gradient, to which the voltage-sensitive channels governing the initiation of the action potential respond. It is pointed out here that the changes in ionic concentration observed in pathophysiology are not incompatible with the idea that the associated changes reflect regulatory events in the extracellular fluid designed to preserve excitability.

Animals↗
PubMed1993

The membrane defect in hereditary stomatocytosis.

Hereditary stomatocytosis and allied conditions represent a series of diseases in which abnormal movements of univalent cations across the plasma membrane play an important part in cellular disease. The primary problem lies not in the active transporters but in the basal permeability of the membrane, which is always increased, and the extent of the increase correlates with the cellular dysfunction. A number of structural abnormalities have been described in these membranes, but the most consistent and convincing is the deficiency of a hitherto uncharacterized integral membrane protein of molecular weight 31 kDa in the severe, 'overhydrated' form of the disease. The true function of this protein remains enigmatic, but its deficiency in this condition indicates that it may have a role in the regulation of cation transport.

Adult↗
PubMed1993

Effect of high voltage pulsed galvanic stimulation on sacral transcutaneous oxygen tension levels in the spinal cord injured.

Evidence is mounting that spinal cord injured (SCI) persons may be at increased risk of pressure ulcers due to prolonged immobilization together with the injury-induced loss of sympathetic tone and decreased vascular resistance. With a view to developing a new method of preventing pressure ulcers, the objective of this study was to determine whether high voltage pulsed galvanic stimulation (HVPGS) could increase sacral transcutaneous oxygen tension (PtcO2) in SCI persons lying prone and supine. In experiment 1, HVPGS applied to the back at spinal level T6 led to a sustained, dose-related increase in sacral PtcO2 in 3 subjects lying prone. In experiment 2, carried out on 29 subjects lying supine on egg-crate mattresses, HVPGS (75 volts, 10 Hz) produced a 35% increase in sacral PtcO2, from a baseline level (Mean +/- SD) of 49 +/- 21 mmHg to 66 +/- 18 mmHg after 30 minutes of stimulation (F = 39.4, p < .00001). In experiment 3, simulated HVPGS was found to have no effect on sacral PtcO2 in 5 subjects lying supine. In experiment 4, HVPGS was repeated on 10 subjects and its effects found to be highly reproducible. It is hypothesized that HVPGS restores sympathetic tone and vascular resistance below the level of the spinal cord lesion, thereby increasing the perfusion pressure gradient in the capillary beds. Randomized controlled trials are now indicated to determine the efficacy of HVPGS for preventing pressure ulcers.

Adolescent↗