MODY 2 causado por mutaciones en la glucoquinasa: una aproximación a nivel molecular / MODY 2 caused by glucokinase mutations: a molecular approach

La diabetes MODY 2 es un tipo de diabetes monogénica producida por una mutación en la enzima glucoquinasa, generando un fenotipo hiperglicémico. Para posibles fines terapéuticos o de diagnóstico, se debe conocer esta proteína, una enzima monomérica de la familia de las hexoquinasas, encargadas de convertir glucosa en glucosa-6-fosfato, el primer paso de la glicolisis. La glucoquinasa se caracteriza por sus propiedades cinéticas únicas: tiene una afinidad mucho menor por el sustrato que las demás hexoquinasas y no es inhibida por su producto. Se encuentra principalmente en páncreas e hígado (ßGK y LGK, respectivamente), donde como sensor regula los distintos estados metabólicos de estos tejidos, y controla la glicemia a nivel sistémico. Las formas ßGK y LGK se diferencian a nivel transcripcional, pues el gen posee dos promotores distintos, específicos para cada tejido. A nivel hormonal, la actividad de esta enzima es regulada selectivamente de manera tejido-específica por glucosa, insulina y otras proteínas reguladoras. La isoforma hepática puede ser secuestrada hacia el núcleo por la proteína reguladora de glucoquinasa (GKRP, por su sigla en inglés). La principal característica de la enzima glucoquinasa es su inusual regulación alostérica, propiedad que le permite adoptar dos conformaciones principales, una cerrada (activa) y otra súper-abierta (inactiva). Se han desarrollado distintas drogas activadoras de glucoquinasa, las cuales se unen al sitio alostérico de la enzima y estabilizan a la proteína en su estado cerrado. En esta revisión se describen las características estructurales y propiedades regulatorias que posee la enzima glucoquinasa, relacionándolas con su rol en el desarrollo de la diabetes MODY 2. También se profundiza en las implicancias moleculares de algunas mutaciones descritas que originan MODY 2, y se abordan los efectos de moléculas activadoras de glucoquinasa.

Diabetes MODY 2 or GCK-MODY is a type of monogenic diabetes produced by a mutation in the glucokinase enzyme, generating a hyperglycemic phenotype. This protein, a monomeric enzyme of the hexokinase family, is responsible for converting glucose into glucose-6-phosphate, the first step of glycolysis. Glucokinase is characterized by its unique kinetic properties: it has a much lower affinity for its substrate than other hexokinases and is not inhibited by its product. It is found mainly in pancreas (ßGK) and liver (LGK), where it acts as a sensor regulating the different metabolic states of these tissues, and ultimately, controlling systemic glycemia. The two forms ßGK and LGK differ at a transcriptional level, because the gene presents two different tissue-specific promoters. The activity of glucokinase in liver and pancreas is regulated by glucose, insulin and other regulatory proteins. The liver isoform can be sequestered to the nucleus by the glucokinase regulatory protein (GKRP). The main characteristic of the enzyme is its unusual allosteric regulation, a property that allows the protein to adopt a closed (active) conformation, and a super-open (inactive) conformation. Different glucokinase activating drugs have been developed, which bind to the allosteric site of the enzyme and stabilize glucokinase in its closed state. This review describes the structural and regulatory properties of the glucokinase enzyme, and its role in the development of MODY 2 diabetes. The molecular implications of some mutations that originate MODY 2 are also described, and the effects of glucokinase activating molecules are addressed.

Hallazgo de una nueva mutación en una familia chilena con diabetes monogénica: caso clínico / Finding of a new mutation in a Chilean family with monogenic diabetes: report of one case

We report a 21 years old woman, without offspring, with diabetes mellitus diagnosed at 17 years of age, without ketosis or weight loss. Her body mass index was 18 kg/m2. Her C peptide was normal (2.3 ng/ml) and diabetes mellitus type 1 autoantibodies were negative. A monogenic diabetes Maturity Onset Diabetes of the Young (MODY) was proposed. Her family study disclosed a diabetic father and a brother with altered fasting glucose levels. The University of Exeter score for MODY yielded a 75.5% probability of MODY2. In the genetic-molecular study of the glucokinase gene (MODY2), the patient had a mutation at position 1343 of exon 10, corresponding to a heterozygous substitution of guanine by adenine (1343 G >A). The same mutation was found in her father and brother. This mutation is different from those previously described in the literature. The described change determines that a glycine is replaced by aspartic at amino acid 448 of the enzyme (non-synonymous substitution). The diagnosis of MODY2 was therefore confirmed in the patient and her father. The mutation was inherited by paternal line.

Nuevas perspectivas en la genética de la diabetes mellitus tipo 2 y sus complicaciones crónicas / New perspectives in the genetics of diabetes mellitus and its complications

This review describes the advances in the knowledge about the genetic aspects of common chronic complications of diabetes with prognostic significance, such as diabetic nephropathy and cardiovascular diseases. It is well known that the genetic factors responsible for chronic complications are different from those that cause diabetes mellitus. Until recently, the studies were limited to the analysis of individual genes associated or related to multifactorial diseases. However at the present time the "genome wide association studies" lead to a great advance in knowledge. The analysis of genetic variations or polymorphisms allows the understanding of human individuality and the predisposition towards certain diseases. A new research field appeared in 2004, when small messenger RNAs, called microRNA related to diabetes mellitus and its chronic complications, were identified. The function of these RNAs is to regulate several target genes. These affect insulin secretion and action and genes related to microangiopathic and specific macroangiopahic complications. This new knowledge will identify new genes related to the disease and will allow the development of therapeutic strategies devised according to individual susceptibility towards specific chronic complication.