LabPLUS is part of Auckland District Health Board
and provides medical laboratory testing
| Services |
MOLECULAR GENETICS TESTS - SPINOCEREBELLAR ATAXIA PANEL |
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| Background: The autosomal dominant cerebellar ataxias (ADCAs) encompass a clinically and genetically heterogeneous group of disorders characterised by progressive cerebellar ataxia and variable association of other neurological signs. Together, the SCA1, SCA2 and SCA3/MJD trinucleotide repeat expansions may account for 40% to more than 60% of Type I ADCA. Type II ADCA (associated with mutations in SCA7) has retinal degeneration as an associated finding, whereas ADCA Type III shows pure cerebellar ataxia of later onset. Mutation frequencies depend on the geographic and ethnic origin of the population studied. Because the SCAs are a genetically heterogeneous group of neurodegenerative disorders, the absence of a repeat expansion at the SCA1, SCA2 or SCA3/MJD, SCA6 and SCA7 loci does not eliminate the diagnosis of one of the other forms of SCA. For predictive testing, therefore, it is necessary first to document the presence of a CAG-repeat amplification in an affected family member to confirm that molecular expansion is the underlying mechanism of disease transmission in the family.
** Machado-Joseph disease (MJD) and SCA3 are each caused by CAG repeat expansion in SCA3 at 14q32.1, yet the disorders can be distinguished clinically by the presence of dystonia, rigidity and bulging eyes in MJD. The genetic explanation for the phenotype variation has not been determined. The clinical features of SCA6 consist predominantly of limb and gait dysarthria, nystagmus and mild vibratory and proprioceptive sensory loss. Although SCA6 does not exhibit such a phenotypic variability as MJD, genetically proven patients with SCA6 sometimes have double vision, increase or decrease in the deep tendon reflex and divergence analysis. SCA7 type ataxia is typically characterised by retinal degeneration. Gonadal instability of the CAG repeats is greater than that observed in any of the seven known neurodegenerative diseases caused by translated CAG repeat expansions and is markedly associated with paternal transmissions. Analysis:
Blood: 3 x 4.0mL whole blood into EDTA tubes . Invert several times to mix. Forward within 24-48 hours at ambient temperature. Paediatric Samples: Minimum of 3mL whole blood in EDTA tubes. Prenatal Samples:
200 mg of tissue. Specimen must be snap frozen within one hour of collection. Send specimen frozen on dry ice. Paraffin blocks of tissue are also acceptable. The tissue sample should not have had prolonged immersion in formalin before embedding. NOTE:
6 weeks once sample is received. Cost of test: SCA Panel - $985 Note: Prices excludes GST (12.5%) and may change without notice. Please click on a link below to view information about another specific test.
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