x fragil fenotipo conductual

SÍNDROMEORIGINAL
X FRÁGIL

¿Se puede atribuir el fenotipo conductual del síndrome X frágil
al retraso mental y al trastorno por déficit de atención/hiperactividad?
J. Artigas-Pallarés, C. Brun-Gasca
CAN THE BEHAVIOURAL PHENOTYPE OF FRAGILE X SYNDROME BE ATTRIBUTED
TO MENTAL RETARDATION AND TO ATTENTION DEFICIT HYPERACTIVITY DISORDER?
Summary. Introduction. Fragile X syndrome (FXS) reveals itselfas dysmorphic stigmata, systemic manifestations, neurological symptoms and cognitive-behavioural manifestations. Mental retardation (MR) and attention deficit hyperactivity disorder
(ADHD) nearly always appear as examples of this last case, but most patients also present a series of fairly common
behavioural characteristics. The most characteristic types of conduct seen in FXS include: languageproblems, lack of
attention, hyperactivity, anxiety, shyness, behavioural problems, stereotypical hand flapping, gaze aversion, obstinacy and
aggressiveness. Aims. The purpose of this work is to determine which behavioural aspects of the syndrome are linked to the
genetic specificity and are not, therefore, determined by MR and ADHD. Patients and methods. Three groups of patients were
compared: 30children diagnosed as suffering from FXS, 30 children with MR caused by diverse aetiologies and 323 children
diagnosed as suffering from ADHD. Results. It was found that there were no significant differences between the IQ and the
age of the FXS and MR groups. To determine the behavioural characteristics of the three groups the parents of the patients
answered Achenbach’s CBCL/4-18 survey.Conclusions. The results obtained show that certain types of conduct that are very
typical of FXS are represented significantly more frequently in the FXS group than in the groups of patients with MR and
ADHD. This behaviour includes: timidity, attachment to adults, shyness, repetition of certain actions over and over again,
pronunciation and speech problems, fear of animals, situations or places, andconcern for tidiness and cleanliness. These
findings lend support to the idea that the behavioural phenotype of FXS is linked to the genetic disorder and is not, therefore,
a consequence of MR or ADHD. [REV NEUROL 2004; 38: 7-11]
Key words. ADHD. Attention deficit hyperactivity disorder. Behavioural phenotype. Fragile X syndrome. Mental retardation.

INTRODUCCIÓN

PACIENTES Y MÉTODOS

Los niños yniñas afectados del síndrome X frágil (SXF) tienen
una conducta que suele ser bastante característica. Los patrones
de conducta que corresponden a un síndrome de base genética se
denominan fenotipos conductuales. La conducta propia del SXF
se caracteriza por: problemas de lenguaje, falta de atención, hiperactividad, ansiedad, timidez, problemas de conducta, estereotipia de aleteo de manos, evitaciónde la mirada, tozudez y agresividad [1,2]. El fenotipo cognitivoconductual del SXF se enmarca
en un retraso mental (RM) de grado medio. El cociente intelectual
(CI) de los individuos afectados de SXF se relaciona con la disminución de producción de FMRP, proteína codificada por el gen
FMR1, responsable del SXF [3].
Si bien se admite que existe una correlación entre la mutación del
gen y el fenotipoconductual, se podría argumentar que, teniendo en
cuenta que en el SXF se presentan, de forma casi constante, RM y
trastorno por déficit de atención/hiperactividad (TDAH), el resto de
síntomas conductuales podría ser un subproducto de dichos trastornos. Con ello, las conductas del SXF dejarían de ser específicas y, por
tanto, no estarían directamente conectadas con la mutación genética.
Elobjetivo de este artículo es determinar si algunos aspectos
del fenotipo conductual no pueden explicarse por el déficit intelectual y el TDAH, en cuyo caso, dada la constancia de los mismos en el SXF, debería admitirse que vienen determinados por la
especificidad genética del síndrome.

Se comparó la conducta de los pacientes con SXF con dos grupos control:
1. Grupo control de pacientes con RM de...