Spinocerebellar degeneration may be predominantly of the spinal form, spinocerebellar form or cerebellar form. The common diseases in this group are:
1. Friedreich’s ataxia and its variations.
2. Olivo-pontocerebellar degeneration (OPCD).
3. Roussey-Levy syndrome.
4. Bassen-Kornzweig syndrome.
5. Refsum’s syndrome.
6. Marie’s ataxia.
7. Dyssynergia cerebellaris myoclonica.
8. Shy-Dagger syndrome.
9. Ataxia telangiectasia.
10. Vitamin E deficiencies.
11. Hereditary spastic paraparesis.
Gene for Friedreich’s ataxia is tightly linked to a marker on chromosome 9. It is an autosomal recessive disorder. The rate of prevalence of this disease is 2-4/1Lac. This has been related to an unstable mutation of X 25 gene on the chromosome 9q13-q21.1. There is abnormal function of mitochondrial ATP
Age of onset is 10-30 years-the commonest variety. There will be marked truncal ataxia and ataxia of the lower limbs with a characteristic ataxic or reeling gait. Gradually the upper limbs are also involved. Intention tremor and nystagmus (25%) are present. Speech may be dysarthric and in course of time scanning speech appears. Jerks are usually lost and plantar reflexes become extensor. Muscular hypotonia is present. Joint sense, vibration sense and sense of position may be affected particularly in the lower limbs.
Optic atrophy (30%) and dementia may be present in some of the cases. Bilateral pes cavus, scoliosis, spina bifida, etc. may also be seen. Cardiomyopathy. heart block, evidences of heart failure and some other ECG abnormalities are also seen. Death is usual before the age of 40.
Progressive ataxia, nystagmus, adiadochokinesia, dysmetria and dysarthria develop in the adult life. Intellectual deterioration, optic atrophy, spasticity are also associated.
Clinically it resembles Friedreich’s ataxia but plantar reflex is not extensor in type, sense of position and vibration sense are retained, nystagmus and dysarthria are also absent.
It differs from Friedreich’s ataxia by the presence of marked steatorrhoea, acanthocytosis and abetalipoproteinaemia.
In addition to features of Friedreich’s ataxia there are retinitis pigmentosa, optic atrophy, perceptive deafness and elevated serum phytanate.
Vitamin E deficiency
A disorder similar to Friedreich’s ataxia has been described. There will be posterior column degeneration which may give rise to ataxia of limbs, areflexia, slurred speech, etc. Retinal pigmentary changes may occur. The disease may occur due to malabsorption or hereditary basis. Treatment is by Vitamin E.
Hereditary spastic Paraparesis
In some families isolated paraparesis may run but there is variable inheritance. There may be cerebellar sign, optic atrophy, pes caves, wasting of hand muscles.