Childhood-onset ataxia: testing for large CAG-repeats in SCA2 and SCA7.
Infantile- and juvenile-onset spinal cerebellar ataxia (SCA) is associated with expansion of 130 to more than 200 CAG-repeats in the SCA2 and SCA7 genes. Routine clinical assays for SCA2 and SCA7, which use polymerase chain reaction (PCR) and denaturing PAGE (polyacrylamide gel electrophoresis), will not reliably detect such large expansions. An assay based on separation of PCR products on an agarose gel, blotting, and hybridization with a (CAG)6 oligonucleotide probe was used to test DNA from individuals more than 10 years of age who had a possible diagnosis of SCA. Among 25 cases, the PCR-blot assay confirmed the presence of SCA2 expansions between 230 and 500 repeats in four unrelated individuals, but did not detect any cases of extreme expansion in the SCA7 gene. The PCR-blot assay provides reliable detection of extreme expansion mutations. Routine incorporation of this assay in clinical laboratories may reveal that infantile-juvenile forms of SCA2 and SCA7 are more prevalent than previously recognized.
Division of Laboratory Genetics, Mayo Clinic, Rochester, Minnesota 55905, USA.
Rong
R
Mao
Arthur S
AS
Aylsworth
Nicholas
N
Potter
William G
WG
Wilson
Galen
G
Breningstall
Myra J
MJ
Wick
Dusica
D
Babovic-Vuksanovic
Martha
M
Nance
Marc C
MC
Patterson
Christopher M
CM
Gomez
Karen
K
Snow
D017668:Age of Onset; D000067719:Ataxin-7; D000067528:Ataxins; D002524:Cerebellar Ataxia / Q000235:genetics* / Q000473:pathology; D002648:Child; D002675:Child, Preschool; D004247:DNA / Q000737:chemistry / Q000235:genetics; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D009419:Nerve Tissue Proteins / Q000235:genetics*; D011506:Proteins / Q000235:genetics*; D017422:Sequence Analysis, DNA; D019680:Trinucleotide Repeat Expansion / Q000235:genetics; D018911:Trinucleotide Repeats / Q000235:genetics*
C000593829:ATXN7 protein, human; D000067719:Ataxin-7; D000067528:Ataxins; D009419:Nerve Tissue Proteins; D011506:Proteins; D004247:DNA