Partial dystrophin deficiency in monozygous twin carriers of the Duchenne gene discordant for clinical myopathy.
We studied monozygous twin women, age 63. One, asymptomatic, had a serum creatine kinase (CK) level of 191 units (normal, 1 to 50); her son died of typical Duchenne muscular dystrophy (DMD) at age 18. Her twin sister had symptomatic limb weakness from about age 40. Her serum CK was 495 units. EMG and muscle biopsy were compatible with myopathy. In the asymptomatic twin, the peripheral blood lymphocyte karyotype was 46,XX. In the affected twin, 18% of cells were 45,X, and the others 46,XX, without X/autosome translocation. DNA analysis did not reveal a deletion at the DMD locus. Immunologic studies of dystrophin showed a partial deficiency of the protein that was more severe in the symptomatic twin. The clinical discordance and the different severity of dystrophin deficiency may have resulted from the effects of lyonization.
Department of Neurology, Columbia University, College of Physicians and Surgeons, New York, NY 10032.
E
E
Bonilla
D S
DS
Younger
H W
HW
Chang
U
U
Tantravahi
A F
AF
Miranda
R
R
Medori
S
S
DiMauro
D
D
Warburton
L P
LP
Rowland
D003402:Creatine Kinase / Q000097:blood; D004200:Diseases in Twins; D016189:Dystrophin; D005260:Female; D006580:Genetic Carrier Screening; D006801:Humans; D008297:Male; D008875:Middle Aged; D009124:Muscle Proteins / Q000032:analysis / Q000172:deficiency / Q000235:genetics*; D009132:Muscles / Q000166:cytology / Q000473:pathology; D009136:Muscular Dystrophies / Q000235:genetics*; D012508:Sarcolemma / Q000648:ultrastructure; D014430:Twins, Monozygotic
D016189:Dystrophin; D009124:Muscle Proteins; D003402:Creatine Kinase