Deleción intersticial del brazo largo del cromosoma 4(4q12q21.1): comunicación de un nuevo caso / Intersticial deletion of the long arm of chromosome 4(4q12-q21.1): report oa a new case

Se comunica un nuevo caso de deleción proximal del brazo largo del cromosoma 4 de novo, en un niño de 3 años de edad con rasgos fenotípicos compatibles con un síndrome de Waardemburg tipo II. Presentaba mechón de pelo blanco frontal, hipoacusia neurosensorial bilateral, desplazamiento lateral de cantos internos, heterocromía de iris, fisura velopalatina, lesiones hipocrómicas en tronco, hipotonía axial, extremidades cortas, deformidades de cuerpos vertebrales, retraso mental y ponderoestatural, reflujo gastroesofágico, síndrome de malabsorción, panhipopituitarismo, comunicación interauricular tipo ostium secundum, hipermetropía (11 dioptrías) y dificultad para la deglución. El cariotipo de alta resolución realizado en células de sangre periférica y piel hipo/hiperpigmentada puso de manifiesto una deleción intersticial en el brazo largo del cromosoma 4 (4q12-q21.1). El estudio mutacional del gen MITF (Waardenburg II) fue normal. Se revisan los casos similares descritos anteriormente en la bibliografía y se resalta que la asociación retraso mental y ponderoestatural en niños con rasgos fenotípicos que recuerdan al síndrome de Waardenburg o al piebaldismo aislado deben alertar sobre posibles deleciones en la estructura del brazo largo del cromosoma 4(AU)

We report a new case of a de novo interstitial deletion of the long arm of chromosome 4, in a three-year-old boy, with phenotypic features compatible with Waardenburg syndrome type II. Clinical examination disclosed the following abnormalities: white forelock, sensorineural hearing loss, hypertelorism, irisheterochromia, cleft palate, hypotonia, depigmented areas in trunk, short limbs and deformities in vertebral bodies, mental retardation and developmental delay. Further studies showed gastroesophageal reflux, malabsorption syndrome, panhypopituitarism, atrial septal defect, hypermetropia (11 diopters) and swallowing difficulties. Chromosome analysis of peripheral blood cells and hypopigmented and hyperpigmented skin cells showed an interstitial deletion of the long arm of chromosome 4 (4q12-q21.1). The results of the mutational study of the MITF gene (Waardenburg II) were normal. Genetic studies of the parentsal so produced normal results. We have reviewed similar cases previously published in the literature, and we stress the fact that the association of growth failure and mental retardation in children with a phenotype resembling piebald trait or Waardenburg syndrome should alert us to the possibility of deletions in the structure of the long arm of chromosome 4(AU)

The role of GABA(A) receptors in the development of alcoholism.

Alcoholism is a common, heritable, chronic relapsing disorder. GABA(A) receptors undergo allosteric modulation by ethanol, anesthetics, benzodiazepines and neurosteroids and have been implicated in the acute as well as the chronic effects of ethanol including tolerance, dependence and withdrawal. Medications targeting GABA(A) receptors ameliorate the symptoms of acute withdrawal. Ethanol induces plasticity in GABA(A) receptors: tolerance is associated with generally decreased GABA(A) receptor activation and differentially altered subunit expression. The dopamine (DA) mesolimbic reward pathway originating in the ventral tegmental area (VTA), and interacting stress circuitry play an important role in the development of addiction. VTA GABAergic interneurons are the primary inhibitory regulators of DA neurons and a subset of VTA GABA(A) receptors may be implicated in the switch from heavy drinking to dependence. GABA(A) receptors modulate anxiety and response to stress; important elements of sustained drinking and relapse. The GABA(A) receptor subunit genes clustered on chromosome 4 are highly expressed in the reward pathway. Several recent studies have provided strong evidence that one of these genes, GABRA2, is implicated in alcoholism in humans. The influence of the interaction between ethanol and GABA(A) receptors in the reward pathway on the development of alcoholism together with genetic and epigenetic vulnerabilities will be explored in this review.

A review of protein structure and gene organisation for proteins associated with mineralised tissue and calcium phosphate stabilisation encoded on human chromosome 4.

Several proteins associated with mineralised tissue (teeth and bone) or involved in calcium phosphate stabilisation in the body fluids, milk and saliva have been mapped to the q arm of human chromosome 4. These include the dentine/bone proteins dentine sialophosphoprotein (DSPP), dentine matrix protein 1 (DMP1), bone sialoprotein (BSP), matrix extracellular phosphoglycoprotein, osteopontin (OPN), enamelin, ameloblastin, milk caseins, salivary statherin, and proline-rich proteins. The proposed function of those that are multiphosphorylated is: (i) the stabilisation of calcium phosphate in solution (e.g. casein, statherin) preventing spontaneous precipitation and seeded-crystal growth or (ii) promoting biomineralisation (e.g. the phosphophoryn domain of DSPP), where the protein described as a template macromolecule, is proposed to act as a nucleator/promoter of crystal growth. The genes of these proteins have been subjected to conserved chromosomal synteny during mammalian evolution. The multiphosphorylated proteins statherin, caseins, phosphophoryn, BSP and OPN have been characterised as intrinsically disordered. The codon usage patterns for the amino acid serine reveal a bias for AGC and AGT codons within the human genes dspp, dmp1 and bsp, mouse dspp and dmp1 but not significantly for statherin or caseins. This pattern was also observed in the gene encoding hen phosvitin that also contains stretches of multiphosphorylated serines and in the dmp1 gene sequences of mammalian, reptilian and avian classes. In conclusion, these intrinsically disordered multiphosphorylated proteins are the translation products of genes displaying examples of codon usage bias, internal repeats and conserved chromosomal synteny within the mammalian class.

Suppression of X-ray-induced chromatid breaks in human tumor cells by introduction of normal chromosome 4.

Human tumor cells in culture frequently show an infinite lifespan and are characterized by an abnormally high frequency of chromatid breaks after x-irradiation during G(2) phase of the cell cycle. This abnormally high frequency of persistent chromatid breaks results from deficient repair of the radiation-induced DNA damage. In three of four tumor cell lines, addition of a single human chromosome 4 from normal cells by microcell fusion resulted in efficient repair as evidenced by suppression of radiation-induced chromatid breaks to the level in normal cells. With respect to senescence-related gene (s), two of these four tumor cell lines belonged to complementation group A and one each to groups C and D. Chromosome 4 restored DNA repair efficiency in only one of the two tumor cell lines of complementation group A. These results suggest that chromosome 4 carries a DNA repair gene or gene(s) that complement the repair deficiency in three of these four tumor lines. Furthermore, the gene(s) involved in cellular senescence on chromosome 4 appear to differ from the gene(s) for repair of radiation-induced DNA damage during G(2).

Interphase chromosome domain re-organization following irradiation.

PURPOSE: To investigate chromosome domain movements during interphase in stationary cell nuclei. MATERIALS AND METHODS: Contact-inhibited primary human fibroblasts were irradiated with 4.0 Gy X-rays, BrdU was added, and air-dried cell preparations made at intervals up to 48 h. Chromosome 4 domain signals (1, 2 and >2) in BrdU negative nuclei (almost exclusively G0/G1) were counted using FISH. A similar experiment was performed using unstimulated human lymphocytes. RESULTS: A very significant rise in nuclei with >2 signals was found within 1 h after radiation. The frequencies observed were in very good agreement with those expected for simple and complex interchanges involving chromosome 4, scored at metaphase in these materials. CONCLUSIONS: The observations constitute evidence for significant domain movement and re-organization within a short time of radiation exposure in G0/G1 interphase nuclei, presumably induced by the formation of inter-domain exchanges. Such re-organization must be a very complicated and delicate topological problem for relaxed chromatin, and must have an important bearing on the interpretation of mechanistic premature chromosome condensation experiments performed whilst it is in operation.

Actitudes de las personas en riesgo de tener enfermedad de Huntington ante el consejo Genético y la posibilidad de Diagnóstico Molecular Predictivo / Attitudes of persons art risk for Huntington's disease towards predictive diagnosis

El consejo genético en la Enfermedad de Huntington ha sido siempre díficil por su gravedad, carácter hereditario y falta de tratamiento. El gen responsable de esta enfermedad se ha localizado en los brazos cortos del cromosoma 4, lo que ha permitido hacer el diagnóstico predictivo y prenatal. Esto ha traído problemas éticos al consejo genético, ya que es posible detectar portadores con elevada confiabilidad, pero aún no existe tratamiento preventivo ni curativo. En este trabajo se estudiaron a 20 familiares en riesgo de tener enfermedad de Huntington mediante un cuestionario de 6 reactivos con objeto de conocer sus actitudes ante el consejo genético y la posibilidad de diagnóstico molecular predictivo. Todos los pacientes mostraron sentimientos de tristeza y/o angustia al saberse en riesgo y 85 por ciento de ellos expresaron deseo de tener el diagnóstico predictivo.

Desensitization of human endothelin A receptor.

The response of G-protein-coupled receptors is modulated by homologous desensitization. Because endothelin A receptor (ETA) plays a part in vasoconstriction, the extent of desensitization and resensitization of endothelin responsiveness was studied. A cDNA clone encoding human ETA receptor was isolated based on similarities to bovine endothelin A receptor. Xenopus laevis oocytes injected with cloned mRNA transcripts were used as a model system for analyzing desensitization. Human neurokinin A (NKA) receptor was used for comparison with ETA receptor in desensitization experiments. Xenopus laevis oocytes injected with the two receptor mRNAs show homologous desensitization but variable rates of recovery. Human NKA receptors desensitize within 5 min and resensitize after 20-30 min. Human ETA receptors also desensitize within 5 min but have a prolonged resensitization period lasting 1.5-2 h. Such a prolonged recovery period is unique to this class of receptors and may serve to regulate some of the deleterious effects mediated by the ETA receptor. The mechanism of differential desensitization is being investigated using genetically engineered mutants of human ETA receptor.