SCA3Spinocerebellar Ataxia type 3 (also known as Machado-Joseph Disease)
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Clinical findings in the more common types of SCA in the SA cohort * Clinical features SCA1 SCA2 SCA6 SCA7 Gait ataxia + + + + Limb ataxia + + + + Dysarthria + + + + Progressive disabling visual impairment + Maculopathy + Pigmentary retinopathy + Supranuclear ophthalmoplegia + + + Diplopia with inability to maintain ocular fixation + Reduced smooth pursuit eye movements + + Slow saccadic eye movements + + Brisk tendon reflexes/spasticity + + Sensory peripheral neuropathy + + Cognitive impairment (late) + + * SCA3 and SCA17 excluded owing to insufficient clinical data.
The hybridization probes for SCA2 and SCA3 were designed against the conserved region located by using the clustalW alignment tool.
Following are the primers and probes designed for the specific diagnosis of SCA2 and SCA3 Subtypes.
For this we have developed the common primers (Table 3), out of which one will amplify the SCA2 gene and another will amplify the SCA3 gene.
The primers are reverse primer that will amplify the SCA2 and SCA3 (normal, mutants and variants).
In Kolkata, two studies, reported SCA2 as the most common mutation (14, 17), while another study done in the same region on 14 families from Bengal reported SCA3 as the most frequent mutation (18).
At the SCA3 locus the repeat allele range was from 14-78 repeats.
The presence of a large number of SCA3 probands suggested that the syndrome is not as rare in India as previously suggested (25).
SCA3 is the most common diagnosis worldwide; accounting for 20-50 per cent of all cases, but is thought to be rare in India (25).
In general, SCA1 and 2 seem to be the most frequent mutation in populations of Caucasian ancestry, while SCA3 and DRPLA are more common in populations of far Eastern ancestry (26).
In our sample, majority (> 60%) of the SCA1 probands were from the interior Deccan region (Mysore, Andhra Pradesh, northern parts of Tamil Nadu), while more than half of the SCA3 probands were from northern Karnataka.
Secondly, a screen for these three common expansions at SCA1, SCA2 and SCA3 loci provided a confirmatory diagnosis for only 40 per cent of the samples.