[MIM 254 770]

(Janz syndrome, JME)

Rare. Subtype of idiopathic generalized epilepsies that constitutes approximately 25% of cases. There is a large genetic heterogeneity because this condition may be the result of a mutation of the EFHC1 gene on 6p12-p11 (most frequent form: EJM1), the GABRA1 gene on 5q34-q35 (EJM5),  CACNB4 gene on 2q22-q23 (EJM6),  GABRD gene on 1p36 (EJM7) or the CLCN2 gene on 3q26 (EJM8). Other loci were also found in association with this form of epilepsy: on 15q14 for EJM2, on 6p21 for EJM3, on 5q12-q14 for EJM4 and on 2q33-q36 for EJM9. It seems that this epilepsy is the result of interactions between the myoclonine and the presynaptic calcium channels.

The disease typically begins between the age of 8 and 20 years in previously normal children. Myoclonus appears especially in the morning: very brief  symmetric muscle twitches, which may be repeated for several minutes. Although consciousness is usually intact during crises, a transient mental clouding and even very short absences can be present. A tonic-clonic seizure can occur. Myoclonus are favored by sleep deprivation and alcohol.

Intelligence and neurological status are normal.

Bursts of polyspikes can be observed on EEG without any clinical symptomatology for the patient or members of his family. Light stimulation promotes the onset of paroxysmal crises and  myoclonic discharges.

Treatment: valproate or clonazepam in case of failure. The treatment should be continued on the long-term because the risk of recurrence is important.

Anesthetic implications: 

epileptic patient; check the hemostasis (valproate can lead to disorders of hemostasis). avoid intermittent light stimulation.

References : 

Updated: June 2019