Recurrence risk due to germ line mosaicism: Duchenne and Becker muscular dystrophy.
The presence of multiple affected offspring from apparently non-carrier parents is caused by germ line mosaicism. Although germ line mosaicism has been reported for many diseases, figures for recurrence risks are known for only a few of them. In X-linked Duchenne and Becker muscular dystrophies (DMD/BMD), the recurrence risk for non-carrier females due to germ line mosaicism has been estimated to be between 14% and 20% (95% confidence interval 3-30) if the risk haplotype is transmitted. In this study, we have analyzed 318 DMD/BMD cases in which the detected mutation was de novo with the aim of obtaining a better estimate of the 'true' number of germ line mosaics and a more precise recurrence risk. This knowledge is essential for genetic counseling. Our data indicate a recurrence risk of 8.6% (4.8-12.2) if the risk haplotype is transmitted, but there is a remarkable difference between proximal (15.6%) (4.1-27.0) and distal (6.4%) (2.1-10.6) deletions. Overall, most mutations originated in the female. Deletions occur more often on the X chromosome of the maternal grandmother, whereas point mutations occur on the X chromosome of the maternal grandfather. In unhaplotyped de novo DMD/BMD families, the risk of recurrence of the mutation is 4.3%.
Helderman-van den Enden
A T J M
AT
Center for Human and Clinical Genetics, Leiden UniversityMedical Center, Leiden, the Netherlands.
de Jong
R
R
den Dunnen
J T
JT
Houwing-Duistermaat
J J
JJ
Kneppers
A L J
AL
Ginjaar
H B
HB
Breuning
M H
MH
Bakker
E
E
D005260:Female; D018095:Germ-Line Mutation / Q000235:genetics*; D006801:Humans; D008297:Male; D009030:Mosaicism; D020388:Muscular Dystrophy, Duchenne / Q000235:genetics*; D012008:Recurrence; D012307:Risk Factors