(Rev Med Chile 2013; 141: 80-89).

Background: Prader-Willi syndrome (PWS) is a neurogenetic disease characterized by neonatal hypotonia, retarded mental and motor development (Rev Méd Chile 2005; 133: 33-41).

La msomia 8 es una anornalia cromosornica que en la mayoria de los casos descrttos corresponde a un rnosaico. Sus coracteristicas clinicas varian desde disnorfias discretes hasla malfcrmaciones severas que, par lo general, "ncluyen retardo mental-leve a grave-, disrnorfias faciales tipicas, olteraciones esqueleticas, pliegues palnares y pla^tares profundos, anomalias renales y olras. Con el proposito de iluslrar la variedad de las caracteristicas fenoripicas de estcs anomalias se describen los casos clinicos de cuatro pacientes cuyo diagnostico se confirrno citogeneticamente, tres con trisomia er mosaico y uno con trisornia 8 completa. La solicitud del estudio citogenetico tuvc su origen en la dismorfia, retraso del desarrollo psicomofor a del lenguaje o hipotonia muscular esquetetica. Es irrportante tener en cuenta la variedad de las caracteristicas fenolipicas de esta trisomia, para sospechar correctamente el diagnostico y solicitor oportunamente el estudio cilogenetico. (Pa la bras clave: trisornia 8, variacion fenotipica, moscicismo.) Chromosome 8 trisomy Trisomy 8 is a chromosomal disorder occurrig usually as a mosaicism. The clinical characteristics of affected patienrs are quite variable ranging from mild to severe mental rerardation and dysmorphic features, including facial malformations, skeletal abnormalities, deep palmar and plantar creases and rencl anomalies among most relevan! phenorypic facts. To illustrate this different clinical patterns four cases of trisomy 8 are reported, three of them were mosaics and one was a full trisomy. Patients were referred to study by dismorphic fades, delayed achievement of developmental milestones or speech or hypotonia. Phenorypic variability of this synarame must be token into account in the diagnostic approach of abnormality.

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