Myotonic dystrophy (MDY1)

Myotonic dystrophy is an autosomal dominant
hereditary disease that predominantly affects
the central nervous and muscular systems (1).
The myotonia causes a masklike facies (2). The
disease is very variable and in many families
shows increasing severity in consecutive
generations (anticipation). An increased number
of CTG repeats, more than 50 copies compared
with 5–35 in normal individuals (3), is
found immediately beyond the 3! end of the
gene in affected persons. This is demonstrated
in a Southern blot as an enlarged DNA fragment
(4). (Schematic representation of a Southern
blot at the gene locus D19S95, probe pBBO.7
after DNA cleavage with EcoRI.