For the majority of individuals with myoclonus dystonia, the myoclonus component of the disorder is often the primary and most disabling feature in comparison to the dystonia component. The symptoms of myoclonus dystonia vary substantially in severity. Myoclonus
Myoclonus is characterized by rapid contractions that affect the upper body including the neck, torso and arms, but may also affect the legs. These movements are stimulated by various factors including stress, noise, caffeine, and physical stimuli. Myoclonus can be characterized in multiple ways including neurological basis, muscular activity, and by stimuli. Myoclonus can be positive or negative; positive myoclonus results from brief spurts of muscle activity and negative myoclonus occurs when there is a lack of any muscular activity. Myoclonus is usually classified physiologically to optimize treatment. Myoclonus is a precursor effect to myoclonus dystonia and most commonly begins in childhood or adolescence.Myoclonus is classified as cortical, subcortical, peripheral or spinal. Cortical myoclonus is the most common of these four and affects the upper limbs and face. Myoclonus dystonia has been characterized under subcortical origin, specifically under nonsegmented myoclonus or brainstem myoclonus. Symptoms within this classification include the startle response and reticular reflex myoclonus. Sudden stimuli like noise or touch to areas around the head or chest cause the startle response which will go up the brain stem and down the spinal cord causing jerk-like movements. Hyperekplexia is a heightened brainstem response where an affected person will continue to elicit the same response to a repeated stimuli.
Infantile neuronal ceroid lipofuscinoses (INCL) or Santavuori disease or Hagberg-Santavuori disease or Santavuori-Haltia disease or Infantile Finnish type neuronal ceroid lipofuscinosis or Balkan disease is a form of NCL and inherited as a recessive autosomal genetic trait. The disorder is progressive, degenerative and fatal, extremely rare worldwide – with approximately 60 official cases reported by 1982, perhaps 100 with the condition in total today – but relatively common in Finland due to the local founder effect. Presentation
The development of children born with INCL is normal for the first 8–18 months, but will then flounder and start to regress both physically and mentally. Motor skills and speech are lost, and optic atrophy causes blindness. A variety of neurological symptoms, such as epilepsy and myoclonic seizures, appear. The senses of hearing and touch remain unaffected. The average lifespan of an INCL child is 9–11 years. Causes
It has been associated with palmitoyl-protein thioesterase. Diagnosis
Treatment
Treatment is limited. Drugs can alleviate the symptoms, such as sleep difficulties and epilepsy. Physiotherapy helps affected children retain the ability to remain upright for as long as possible, and prevents some of the pain. Recent attempts to treat INCL with cystagon have been unsuccessful. See also
FAIDD (The Finnish Association on Intellectual and Developmental Disabilities)

References
External links

GeneReviews/NCBI/NIH/UW entry on Neuronal Ceroid-Lipofuscinosis
An overview (in Finnish)
The INCL organization of Finland (in Finnish)