Myotonic dystrophy

Effects of age and gene dose on skeletal muscle sodium channel gating in mice deficient in myotonic dystrophy protein kinase

Myotonic muscular dystrophy (DM) is characterized by abnormal skeletal muscle Na channel gating and reduced levels of myotonic dystrophy protein kinase (DMPK). Electrophysiological measurements show that mice deficient in Dmpk have reduced Na currents in muscle. We now find that the Na channel expression level is normal in mouse muscle partially or completely deficient in Dmpk. Reduced current amplitudes are not changed by age or gene dose, and the reduction is not due to changes in macroscopic or microscopic gating kinetics. The mechanism of abnormal membrane excitability in DM may in part be silencing of muscle Na channels due to Dmpk deficiency.

Increased (CTG/CAG)(n) lengths in myotonic dystrophy type 1 and Machado-Joseph disease genes in idiopathic azoospermia patients

BACKGROUND

An increase in CAG trinucleotide repeat length in the androgen receptor (AR) gene has been linked to idiopathic azoospermia.

METHODS

In order to test whether other (CAG/CTG)(n) loci are also affected, the (CAG/CTG)(n) frequency distribution at myotonic dystrophy type 1 (DM1), Machado-Joseph disease (MJD), dentatorubral-pallidoluysian atrophy (DRPLA) and spinocerebellar ataxia type 8 (SCA8) loci, in addition to the AR gene, was investigated in 48 azoospermia patients and 47 controls.

RESULTS

The median CAG repeat length in the AR gene was significantly longer in azoospermia patients than in controls (23 versus 21, P < 0.001). Significant differences were also noted in the upper tails of trinucleotide repeat length distributions at both DM1 and MJD loci between the two populations. At the DM1 locus, alleles of more than 18 repeats were observed only in azoospermia patients, and not in controls (P = 0.014). At the MJD locus, the frequency of normal alleles (ANs) with 29 or more CAG repeats was also much higher in azoospermia patients (29.2 versus 7.4%; P = 0.0001). However, the repeat length distribution at DRPLA and SCA8 loci did not differ in the two groups.

CONCLUSIONS

These data indicated that, at least in a subset of azoospermia patients, there was an increase in the number of trinucleotide repeats in some disease loci. Thus, it is noteworthy to evaluate whether offspring of these azoospermia patients, if born by assisted reproductive technologies, have an increased risk of trinucleotide repeat diseases.