RT Journal Article
SR Electronic
T1 Sperm DNA analysis in a Friedreich ataxia premutation carrier suggests both meiotic and mitotic expansion in the FRDA gene.
JF Journal of Medical Genetics
JO J Med Genet
FD BMJ Publishing Group Ltd
SP 713
OP 716
DO 10.1136/jmg.35.9.713
VO 35
IS 9
A1 Delatycki, M B
A1 Paris, D
A1 Gardner, R J
A1 Forshaw, K
A1 Nicholson, G A
A1 Nassif, N
A1 Williamson, R
A1 Forrest, S M
YR 1998
UL http://jmg.bmj.com/content/35/9/713.abstract
AB Friedreich ataxia is usually caused by an expansion of a GAA trinucleotide repeat in intron 1 of the FRDA gene. Occasionally, a fully expanded allele has been found to arise from a premutation of 100 or less triplet repeats. We have examined the sperm DNA of a premutation carrier. This man's leucocyte DNA showed one normal allele and one allele of approximately 100 repeats. His sperm showed an expanded allele in a tight range centering on a size of approximately 320 trinucleotide repeats. His affected son has repeat sizes of 1040 and 540. These data suggest that expansion occurs in two stages, the first during meiosis followed by a second mitotic expansion. We also show that in all informative carrier father to affected child transmissions, with the notable exception of the premutation carrier, the expansion size decreases.