High efficiency in the attribution of parental origin of non-disjunction in trisomy 21 by both cytogenetic and molecular polymorphisms

The precise origin of the supernumerary chromosome can be defined in the majority of trisomy 21 cases. This is achieved by evaluating the chromosome 21 short arm polymorphism and analysing restriction fragment length polymorphisms (RFLPs) of multiple chromosome 21 loci. We report a study on 37 Italian families with Down's syndrome. In 35 cases (94.6%) both the parental and the meiotic stage of non-disjunction could be established. Knowledge of the origin of the extra chromosome 21 is a pre-requisite for investigations of genetic or environmental factors that may affect the meiotic process

No evidence of major locus for benign familial infantile convulsions on chromosome 19q12-q13.1.

Summary: Purpose: A locus for benign familial convulsions (BFICs) has been recently mapped on chromosome 19qi2-13.1 by studying five families of Italian descent. The main goal of this study was to investigate the role of this locus in a set of seven newly identified families with at least three affected cases. Methods: Five polymorphic microsatellite markers covering the BFIC locus on chromosome 19q have been typed, and parametric linkage analysis has been performed to analyze the segregation of the BFIC locus within our families. Resulrs: Cumulative 2-point lod scores and multipoint analysis showed no evidence of linkage between chromosome 19 markers and the BFIC phenotype. The analysis of familyspecific 2-point lod scores and haplotypes, however, indicated the presence of linkage to chromosome 19q in a single family, suggesting genetic heterogeneity within our family sample. Conclusions: Our study demonstrates that the previously reported BFIC locus on chromosome 19q12-13.1 is not a major locus for BFICs. We suggest that genetic heterogeneity may have generated our discordant linkage findings, as it was reported in benign familial neonatal convulsions, a related idiopathic mendelian syndrome