SOMATIC MOSAICISM, GERMLINE EXPANSIONS, GERMLINE REVERSIONS AND INTERGENERATIONAL REDUCTIONS IN MYOTONIC-DYSTROPHY MALES - SMALL POOL PCR ANALYSES

In order to characterize the dynamics of CTG repeat instability in som atic and germline tissue from myotonic dystrophy (DM) males we have us ed small pool polymerase chain reaction (PCR) in a detailed quantitati ve analysis of repeat length variation, We demonstrate that the hetero geneous smear of CTG repeats observed in DM patients using standard an alyses is comprised of multiple unresolved bands that may be dissected into discrete length alleles derived from single cells using single m olecule PCR techniques, Analysis of somatic tissues demonstrates a bia s toward increasing allele length and a lower boundary below which var iant alleles are rare, consistent with a highly directional expansion pathway in the soma, Two sperm samples show extensive variation end a size increase bias, concordant with the phenomenon of anticipation, In addition, sperm analysis shows that targe contractions, including rev ersions into the normal size range, are restricted to the germline, De tailed analysis of intergenerational 'reductions' paternally transmitt ed to two offspring suggests that some apparent reductions may be arti facts of somatic expansion in the parent, Our data indicate that in ad dition to germline variation, substantial somatic expansion can also c ontribute to the intergenerational differences usually observed in DM.