Supernumerary marker chromosomes (sSMCs) are a relatively rare cytogenetic phenomenon. Their laboratory examination is often difficult, and the clinical interpretation is even more challenging. The main reason is that most sSMC carriers have no clinical manifestations. The chromosome origin and exact range of the aberration are very important, as well as the fact that sSMCs are often found in mosaics that can strongly influence both the phenotype and the interpretation of result. Prenatal sSMC finding is one of the most challenging situations in both clinical and laboratory genetics. This work deals with the investigation process of sSMC carriers using molecular cytogenetic techniques, especially fluorescence in situ hybridization (FISH). We investigated a total of 67 families collected both prospectively and retrospectively, and we found 70 unique sSMCs in a total of 74 individuals. Six cases were familial and in three cases two sSMCs were found in one individual. According to the initial karyotype finding, the cases were divided into two groups, sSMCs supernumerary to a normal karyotype (group A) and sSMCT s supernumerary to the Turner karyotype (group B). The chromosomal origin was successfully determined in 88,6 % sSMCs. In group A the most common findings were sSMCs derived from chromosome 15,...

El establecimiento de correlaciones entre fenotipo y genotipo es uno de los principales objetivos de la genética. La obtención de un diagnóstico ajustado facilita el manejo clínico del paciente, así como poder ofrecer un correcto consejo genético, con asesoramiento reproductivo a las familias de pacientes con enfermedades genéticas. La identificación de genes asociados a patología desde alteraciones citogenéticas asociadas a fenotipo es uno de los métodos de clonación posicional. En este trabajo nos hemos basado en dos tipos de modelos de anomalías citogenéticas: balanceadas y no balanceadas (translocaciones y cromosomas marcadores). Hemos caracterizado las alteraciones citogenéticas de cinco pacientes de cada modelo con fenotipos diversos, empleando una combinación de técnicas citogenéticas y moleculares, con el objetivo de proponer genes candidatos asociados a cada fenotipo. / One of the main objectives of Genetics is the establishment of phenotype-genotype correlations. A correct diagnosis facilitates the clinical management of the patient and the possibility to offer a genetic counselling, with reproductive assessment to the families with a patient with a genetic disease. The identification of genes associated to pathology from cytogenetic alterations associated to phenotype is one of the methods of positional cloning. In this work we have based in two different models of cytogenetic alterations: balanced and unbalanced anomalies (translocations and marker chromosomes). We have characterized five patients of each group with different phenotypes, using a combination of cytogenetic and molecular techniques, with the objective of establish candidate genes associated to disease.