Un ejemplo se muestra en rosas. El alelo para el color rojo es dominante sobre el alelo para el color blanco, pero las rosas heterocigotas, que tienen ambos alelos, son rosadas. Tenga en cuenta que esto es diferente de la codominancia, que es cuando ambos alelos se expresan al mismo tiempo. Co-dominio se produce cuando los dos alelos en un par heterocigotos son mutuamente dominante o recesivo, lo que significa que ambos se expresan juntos. Esto a menudo puede dejar el par indeterminado, con elementos de cada alelo se expresan en un estado sometido.

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Ileana G. Santos Jussara V. Toniolo Geraldo Medeiros-Neto. Congenital hypothyroidism CH , as seen in the neonatal period, is predominantly caused by defects in the organogenesis athyreosis, ectopic thyroid, thyroid hypoplasia or by specific defects in hormonogenesis dyshormonogenesis.

Central hypothyroidism is rare, being linked to specific transcription factors involved in the maturation of the hypothalamic-pituitary axis or by mutations in the TSH-beta gene. Dyshormonogenesis may be caused by mutation coding for thyroid proteins such as the TSH receptor, the sodium-iodide symporter NIS , the pendrin Pendred's syndrome , thyroid peroxidase TPO , thyroglobulin Tg , thyroid dehalogenase, the receptor for thyroid hormone TR-beta or thyroid transport proteins TBG, transthyretin.

Usually, most of these defective genes will induce a phenotype with goiter and variable degree of hypothyroidism that may be present in the neonatal period or will gradually develop during post-natal life.

Moreover, the genetic expression may be partial or total according to the specific mutation occurring in the involved genes. Keywords: Ectopic thyroid; Thyroid hypoplasia; Dyshormonogenesis; Mutations; Thyroid genes; Congenital hypothyroidism. Muito recentemente, Congdon e cols. O estudo de Vilain e cols. Nos achados de estudos moleculares descritos por Bakker e cols. No Brasil, Santos e cols. Recent insights in the pathogenesis of neonatal hypothyroidism.

Thyroid and Age , Schattauer; ; Developmental abnormalities of the thyroid. In: DeGroot LJ, editor. Philadelphia: W. Saunders; ; La Franchi S. Recent developments in pediatric thyroidology. Thyroid Today ; Physiol Rev ; A family of mammalian anion transporters and their involvement in human genetic diseases. Hum Mol Genet ; Kopp P. Pendred's syndrome and genetic defects in thyroid hormone synthesis. J Biol Chem ; Genetic disorders of the thyroid hormone system.

Genetics in Endocrinology. Guillam MP, Kopp P. Genetic regulation of thyroid development. Curr Opin Pediatr ; Pax genes and their roles in cell differentiation and development. Curr Opin Cell Biol ; Follicular cells of the thyroid gland require PAX8 gene function.

Nature Genet ; Pax-8, a paired domain-containing protein, binds to a sequence overlapping the recognition site of a homeodomain and activates transcription from two thyroid-specific promoters. EMBO J ; PAX8 mutations associated with congenital hypothyroidism caused by thyroid agenesis. A novel mutation Q4OP in PAX8 associated with congenital hypothyroidism and thyroid hypoplasia: evidence for phenotypic variability in mother and child. J Clin Endocrinol Metab ; Autosomal dominant transmission of congenital thyroid hypoplasia due to loss-of-function mutation of PAX8.

Inherent primary hypothyroidism in mice. Science ; Mol Endocrinol ; Resistance to thyrotropin caused by mutations in the thyrotropin-receptor gene. N Engl J Med ; Four families with loss of function mutations of the thyrotropin receptor.

Familial congenital hypothyroidism due to inactivating mutation of the thyrotropin receptor causing a profound hypoplasia of the thyroid gland. J Clin Invest ; Mutations of the human thyrotropin receptor gene causing thyroid hypoplasia and persistent congenital hypothyroidism.

Apparent congenital athyreosis contrasting with normal plasma thyroglobulin levels and associated with inactivating mutations in the thyrotropin receptor gene: are athyreosis and ectopic thyroid distinct entities? Structural analysis of the thyrotropin receptor in four patients with congenital hypothyroidism due to thyroid hypoplasia. Thyroid ; Genetic and linkage analysis of familial congenital hypothyroidism: exclusion of linkage to the TSH receptor.

Hum Genet ; Cloning and characterization of the thyroid iodide transporter. Nature ; Biochem Biophys Res Commun ; Identification of a nonsense mutation producing a downstream cryptic 3' splice site. Matsuda A, Kosugi S. Kosugi S, et al. Failure of membrane targeting causes the functional defect of two mutant sodium iodide symporters.

Pendred's syndrome: clinical characteristics and molecular basis. Curr Opin Endocrinol Diab ; Enlarged vestibular aqueduct: a radiological marker of Pendred syndrome, and mutation of the PDS gene. QJM ; Targeted disruption of mouse PDS provides insight about the inner-ear defects encountered in Pendred syndrome.

Pendred syndrome is caused by mutations in a putative sulphate transporter gene PDS. The Pendred syndrome gene encodes a chloride-iodide transport protein. Pendrin, the protein encoded by the Pendred syndrome gene PDS is an apical porter of iodide in the thyroid and is regulated by thyroglobulin in FRTL-5 cells.

Endocrinology ; Phenocopies for deafness and goiter development in a large inbred Brazilian kindred with Pendred's syndrome associated with a novel mutation in the PDS gene. Clinical and molecular analysis of three Mexican families with Pendred's syndrome. Eur J Endocrinol ; Identification of a mutation in coding sequence of the human thyroid peroxidase gene causing congenital goiter. Two different mutations in the thyroid peroxidase gene of a large inbred Amish kindred: power and limits of homozygosity mapping.

A novel mutation in the TPO gene in goitrous hypothyroidism patients with iodide organification defect. Clin Endocrinol ; Novel mutations of the thyroid peroxidase gene in patients with permanent congenital hypothyroidism.

Defective organification of iodide causing hereditary goitrous hypothyroidism. Molecular analysis of mutated thyroid peroxidase detected in patients with total iodide organification defects. A novel mutation in the human thyroid peroxidase gene resulting in a total iodide organification defect.

J Endocrinol ; Two decades of screening for congenital hypothyroidism in the Netherlands: TPO gene mutations in total iodide organification defects an update. Mutation analysis of thyroid peroxidase gene in Chinese patients with total iodide organification defect: identification of five novel mutations.

Maternal isodisomy for chromosome 2p causing severe congenital hypothyroidism. Two novel missense mutations in the thyroid peroxidase gene RW and GR result in a localization defect and cause congenital hypothyroidism. Nascimento AC. Defective thyroglobulin synthesis and secretion causing goiter and hypothyroidism. Endocr Rev ; A novel missense mutation GR in thyroglobulin causes hypothyroidism in rdw rats. Endocrinology ; A 3'spliced site mutation in the thyroidlobulin gene responsible for congenital goiter with hipotyroidism.

A nonsense mutation causes human hereditary congenital goiter with preferential production of a nt thyroglobulin RNA messenger. Congenital goiter with hypothiroidism caused by a 5' spice mutation in the thyroglobulin gene. Genomic organization of the human thyroglobulin gene: the complete intron-exon structure. Eur J Endocrinol ;


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