Carbohydrate-deficient glycoprotein syndromes

Carbohydrate-deficient glycoprotein syndromes are rare, multisystemic diseases, typically with major nervous system impairment, that are caused by hypo- and unglycosylation of N-linked glycoproteins. Hence, a biochemical evidence of this abnormality, like hypoglycosylation of serum transferrin is essential for diagnosis. Clinically and biochemically, six types of the disease have been delineated. Three of them are caused by deficiencies of the enzymes that are required for a proper glycosylation of lipid--(dolichol) linked oligosaccharide (phosphomannomutase or phosphomannose isomerase or alpha-glycosyltransferase), and one results from a deficiency of Golgi resident N-acetylglucosaminyltransferase II. In addition one variant of the disease has been reported as due to a defective biosynthesis of dolichol iself. The diseases are heritable but genetics has been established for only two types. Therapy, based on administration of mannose to patients is currently under investigation. It benefits patients with deficiency of phosphomannose isomerase. Taking into account the complexity of N-linked glycosylation of proteins more of the disease variants is expected to be found.     

Experimental deafferentation syndromes

Animal models of dysesthesias have been established, and reveal the following major points. Dysesthesias of peripheral nerve or dorsal root origin have a central neural cause. Chronic dysesthesias of spinal origin have a cause which resides in the brain. The origins of these effects are lesions in the spinothalamic system. The causes of these effects are abnormal functionings among opiate, catecholamine, and purine pathways. Denervation supersensitivity is suggested.     

Gastrointestinal polyposis syndromes

Colorectal cancer is one of the leading causes of cancer-related death in the Western society, and the incidence is rising. Rare hereditary gastrointestinal polyposis syndromes that predispose to colorectal cancer have provided a model for the investigation of cancer initiation and progression in the general population. Many insights in the molecular genetic basis of cancer have emerged from the study of these syndromes. This review discusses the genetics and clinical manifestations of the three most common syndromes with gastrointestinal polyposis and an increased risk of colorectal cancer: familial adenomatous polyposis (FAP), juvenile polyposis (JP) and Peutz-Jeghers syndrome (PJS).     

Myelodysplastic syndromes.

The myelodysplastic syndromes are a heterogeneous group of hematopoietic stem cell disorders characterized by dysplastic and ineffective hematopoiesis and a varying risk of transformation to acute leukemia. Although the natural history of these syndromes is variable, several factors appear to be of prognostic importance, including the French-American-British classification, the karyotype, in vitro colony formation, and others. The pathogenesis of the myelodysplastic syndrome is not known, but recent evidence suggests that alterations of cellular oncogenes may be a causative factor. There is no standard therapy for myelodysplasia, and thus novel approaches to patient management are warranted.     

Iron overload syndromes

Iron overload is relatively common and is now detected more frequently because of inclusion of serum iron measurement in automated clinical chemistry panels. Secondary hemosiderosis and hemochromatosis result from increased iron absorption associated with increased erythropoiesis compensating for hemolysis, increased dietary iron, inappropriate prolonged oral iron therapy or chronic multiple transfusions. Primary hemochromatosis is a genetic metabolic disorder associated with the HLA locus on chromosome 6 resulting in increased iron absorption, though erythropoiesis and dietary iron are normal, and abnormal diversion of iron from reticuloendothelial (RE) to parenchymal cells. A genetic increase of intracellular iron carrier is a proposed basic mechanism. Only in the cirrhotic stage of primary hemochromatosis do RE iron and serum ferritin increase. Since both serum iron and serum ferritin may remain normal in the precirrhotic stage and may be falsely positive in the absence of iron overload, direct measurement of body iron stores is often useful. Measurement of tissue iron in liver biopsy specimens is widely used. However, quantitation of total mobilizable body iron by measurement of a 6-hour urine collection after intravenous injection of 59Fe-DTPA is noninvasive, sensitive, relatively accurate, and together with other laboratory and clinical data provides a practical means of establishing the correct diagnosis and therapy early enough to minimize organ damage.     

Chronic pain syndromes

Brainstem-scalp discharge propagation was evaluated in 20 patients with chronic pain, of which 10 were ranked according to the frequency of involved systems making up the chronic pain syndrome. It is concluded that brainstem discharges alone were sufficient to generate the chronic pain syndrome.     

Sleep apnea syndromes

Sleep apnea syndromes have been identified only relatively recently. Their most frequent form is characterized by a sleep-related upper airway obstruction resulting in apneas which may repeat themselves up to several hundred times during a night's sleep. Their mean duration is about 30 to 40 seconds, but some apneas last over one minute. Breathing resumption requires an arousal, which may be clearly identified on the EEG but usually goes unnoticed by the patient. The most immediate consequence are hypoxemia and sleep fragmentation. There may be associated arrhythmias and hemodynamic changes, especially in the pulmonary circulation. The predominant clinical signs are snoring (during the breathing resumption between the apneas) and daytime somnolence due to sleep fragmentation. In addition to the risks of work and traffic accidents, these patients run a long-term risk of cardiovascular accidents. About 20% develop pulmonary hypertension, a contributing factor to right heart failure. About 50% are hypertensive, which combined with a frequently observed polycythemia, makes them vulnerable to ischemic accidents. The treatment is based upon the use of continuous positive airway pressure (CPAP) during sleep. In case of failure, surgical alternatives may be considered.     

Mutant insulin syndromes

Highly sensitive procedures for the characterization of molecular species of insulin in the circulation and for the isolation of the gene encoding human insulin have recently been developed. Nine subjects with abnormal forms of insulin or proinsulin have been reported. These include: [Leu B25], [Ser B24], [Leu A3] insulin as well as others that have not yet been identified. The clinical syndrome associated with the secretion of an abnormal insulin or proinsulin molecule presents with apparent endogenous insulin resistance with inappropriate high levels of insulin for the prevailing blood glucose concentration and a high insulin/C-peptide ratio due to the reduced catabolism of the abnormal insulin molecule. Diabetes occurs if there is concomitant insulin resistance or pancreatic beta cell failure. In addition, abnormal forms of insulin have been found in the insulin autoimmune syndrome presenting with recurrent, self-limiting hypoglycemia. Abnormal insulin in the autoimmune insulin syndrome suggests that abnormalities in endogenous antigens may be important in the formation of antibodies in other autoimmune states. However, although abnormalities in the insulin molecule may provoke the autoimmune response, it is also feasible that the presence of antibodies to normal insulin and proinsulin in some way alters their metabolism to yield abnormal products on high performance liquid chromatography (HPLC). Abnormal forms of insulin have also been found in subjects with reactive hypoglycemia and exogenous insulin-resistance and appear to be transmitted in an autosomal dominant manner. A protocol for the sequence of investigating subjects who potentially harbor a mutant or otherwise abnormal form of insulin using HPLC and recombinant DNA technology is presented.     

Preleukemic syndromes.

Acute nonlymphocytic leukemia (ANLL) is preceded by a hematologic illness representing the "preclinical" stages of the disease in many patients. This "preclinical stage" or preleukemic stage is difficult to recognize by conventional hematologic morphologic techniques. A prospective study was carried out to determine whether cytogenetic studies would be helpful in the recognition of preleukemic states and whether the presence of cytogenetic abnormalities would have prognostic significance. A study of 284 patients with suspected preleukemia has yielded 62 patients with progression to overt ANLL. Cytogenetic abnormalities were found in 30% of suspected preleukemic patients, whereas 53% of the patients progressing to acute leukemia had cytogenetic abnormalities. These studies show that the presence of cytogenetic abnormalities aid in the recognition of preleukemia but are not specific for early leukemia. Patients with cytogenetic abnormalities are more likely to develop overt ANLL. Banded chromosome studies demonstrated cytogenetic abnormalities in the preleukemic phase in 13 of 26 patients. A variety of clonal chromosomal abnormalities were observed.