martes, 21 de agosto de 2007

¿Cómo se produce el Síndrome de Down?


Estoy seguro que la mayoría de los padres o familiares de un niño con Síndrome de Down tienen al menos una remota idea de qué es este síndrome y como se produce. Aún así creo que también hay muchas dudas al respecto. Trataré brevemente de explicar en palabras simples el origen de lo que conocemos como Síndrome de Down.

En primer lugar, un síndrome es un “conjunto de síntomas y signos”. En el caso del Down los signos y síntomas son entre otros, la forma de los ojos, la macroglosia (lengua grande), pliegue palmar único, cuello ancho y corto, hipotonía muscular, retraso mental etc. Se han descrito más de 100 diferentes signos, pero no es necesario que estén todos presentes.

Y, ¿Por qué Down?
Se le llama así debido a que fue John Langdon Haydon Down el primero en hacer la descripción del síndrome (en 1866). Sin embargo recién en 1958 Jérôme Lejeune descubrió que la causa estaba en los “cromosomas”.

Todos nosotros tenemos 46 cromosomas(23 pares) en cada célula, la mitad proviene de nuestra madre y la otra de nuestro padre. Sin embargo los portadores de síndrome de Down en lugar de tener dos cromosomas número 21, tienen tres. Es por esto que se habla de “trisomía 21”. Para entenderlo mejor pueden ver las siguientes imagenes:









Este cromosoma adicional puede originarse de 3 formas:

Trisomía libre o simple. En este caso uno de los padres, es decir, el óvulo o el espermatozoide, entrega al hijo un cromosoma 21 demás, por lo que todas las células del bebé van a tener trisomía 21. Es la forma más común de Síndrome de Down, corresponde al 95 % de los niños.

Translocación. Es similar a la anterior, pero en este caso el cromosoma 21 extra, viene pegado a otro cromosoma, generalmente al número 14. Corresponde al 3-4%.

Mosaicismo. Solo el 1 a 2% de los niños con Síndrome de Down corresponde a lo que se conoce como “mosaico”. A diferencia de lo que ocurren el las dos situaciones anteriores, aquí tanto el espermatozoide como el óvulo tienen la cantidad normal de cromosomas. Luego de la fecundación las células del embrión empiezan a dividirse muchas veces, y en alguna de esas divisiones ocurre un error y aparece un cromosoma 21 adicional. Por lo que algunas células del niño van a tener trisomía 21 y otras van a ser normales.

Cualquiera de las 3 formas va a dar origen al Síndrome de Down. Espero haber sido claro en mi explicación. Si tienen alguna duda, háganmelo saber y trataré de aclararla.

19 comentarios:

Anónimo dijo...

Tengo una primita de 6 años con sindrome de down. Cuando mi tia estaba embarazada tambien estaba enferma de leucemia pero ninguno lo sabia y ella tampoco. Mi pregunta es si la enfermedad pudo provocar el sindrome

torkin dijo...

Cintia, Lamento mucho que tu tía padeciera Leucemia y espero que ahora esté bien.
Debo decirte que eso nada se relaciona con que tu primita naciera con Síndrome de Down.
La Leucemia es una enfermedad hematológica (de la sangre) que no afecta los gametos (óvulos y espermatozoides), por lo que no influye en que los hijos tengan o no el síndrome.

Espero haberte ayudado. Gracias por visitar Mi querido Down

oscar dijo...

Hola Cordial Saludo!
Tengo una Sobrinita que nacio con algunas caracteristicas del sindrome pero los medicos no estan plenamente seguros de ello por consiguiente le estan haciendo varios examenes para ir descartando Mi pregunta es la siguiente si la niña tiene la lengua grande esto que quiere decir? por que esta es una caracteristica del sindrome no? sus orejas son pequeñas y pegadas y su rostro parecido a los niños con el sindrome. Quisiera que me dijera como podemos estar plenamente seguros de esto.
Gracias por la atencion prestada!.

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hola mi no mbre es lourdes preciado y tengo una pequeña de dos añitos con down a nosotros no dijeron que nuestra hija tenia este padecimiento cuando nackio y fue confirmado al mes de nacida por medio del examen de los genes desde un principio me dijeron que iba a ser muy tranquila pero con el paso del tiempo me di cuenta que no es asi ella no se piuede estar quieta ni por un ratito y mi esposo esta diagnosticado con iperactividad mi pregunta res la iperactividad es hereditaria? ya que es la unica respuesta que le encuentro a que sea tan inquieta tambien aprende muy rapido hablando de lo intelectual porquer en lo motriz va un poco lenta ya que para ser tan inquieta todavia no camina me gustaria leer su opinion y adjunto mi msn arisheccid@hotmail.com de ante mano muchas gracias

marcia dijo...

hola soy Marcia hace 40 dias perdi a mi bebe de 6 meses y medio de embarazo por derrame pleural presentaba tambien sindrome de down,mi pregunta es:por que pudo presentar este sindrome si tengo a mi primer hijo de ocho anos normal y sin ningun problema, y que examen debemos hacernos con mi pareja para saber si el proximo no viene acompanado de nuevo de este sindrome

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