Relation between trinucleotide GAA repeat length and sensory neuropathy in Friedreich's ataxia.
OBJECTIVE
To verify if GAA expansion size in Friedreich's ataxia could account for the severity of sensory neuropathy.


METHODS
Retrospective study of 56 patients with Friedreich's ataxia selected according to homozygosity for GAA expansion and availability of electrophysiological findings. Orthodromic sensory conduction velocity in the median nerve was available in all patients and that of the tibial nerve in 46 of them. Data of sural nerve biopsy and of a morphometric analysis were available in 12 of the selected patients. The sensory action potential amplitude at the wrist (wSAP) and at the medial malleolus (m mal SAP) and the percentage of myelinated fibres with diameter larger than 7, 9, and 11 microm in the sural nerve were correlated with disease duration and GAA expansion size on the shorter (GAA1) and larger (GAA2) expanded allele in each pair. Pearson's correlation test and stepwise multiple regression were used for statistical analysis.


RESULTS
A significant inverse correlation between GAA1 size and wSAP, m mal SAP, and percentage of myelinated fibres was found. Stepwise multiple regression showed that GAA1 size significantly affects electrophysiological and morphometric data, whereas duration of disease has no effect.


CONCLUSIONS
The data suggest that the severity of the sensory neuropathy is probably genetically determined and that it is not progressive.
Santoro
L
L
Department of Clinical Neurophysiology, Federico II University, Naples, Italy.
De Michele
G
G
Perretti
A
A
Crisci
C
C
Cocozza
S
S
Cavalcanti
F
F
Ragno
M
M
Monticelli
A
A
Filla
A
A
Caruso
G
G
D000293:Adolescent; D000328:Adult; D000483:Alleles; D001706:Biopsy; D005071:Evoked Potentials; D005621:Friedreich Ataxia / Q000175:diagnosis* / Q000235:genetics*; D006801:Humans; D007866:Leg / Q000294:innervation; D008475:Median Nerve / Q000502:physiology; D009431:Neural Conduction / Q000502:physiology; D012189:Retrospective Studies; D012720:Severity of Illness Index; D013497:Sural Nerve / Q000473:pathology; D013979:Tibial Nerve / Q000502:physiology; D019680:Trinucleotide Repeat Expansion / Q000235:genetics*