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Epilepsy - convulsions

This is a group of disorders in the electrical activity of the brain, manifesting in convulsions. A convulsive episode is the expression of sudden, uncontrolled electrical activity in a specific area in the brain.

Clinical types

There are different types of epilepsy, and the causes are many and diverse:

  1. An environmental, non-genetic cause. Focal damage to the brain as a result of surgery, trauma, or damage from infection or hypoxia can cause convulsions. The environmental causes are not genetic and usually occur during the perinatal period.

  2. Some types of epilepsy have a genetic cause. One type, which is mild, causes febrile (fever-induced) convulsions - these are common, transient, do not require permanent treatment, and leave no damage. There are also more severe hereditary types that span the range of severity up to uncontrollable convulsions that gradually cause brain and developmental damage.

  3. There are a number of syndromes in which, apart from the epileptic focus, there are other disorders or other defects in the brain or in other tissues. These include MERRF (convulsions with muscular disease), convulsions with yellow teeth, convulsions due to benign tumors as seen in tuberous sclerosis, etc. It is important to differentiate these from the non-hereditary types, although this is not always possible.

Clinical signs

The signs vary according to the location and function of the region of the brain in which the irregular electrical activity occurs and the scope of the spread of this electrical activity to other regions of the brain.

In most cases, the cause is unknown. An environmental cause can be suspected if there is a clear-cut history of a disruption in the oxygen supply to the brain (hypoxia), such as an infection or cerebral hemorrhage.

A genetic cause should be considered if there is no known environmental cause, especially if there are other cases in the family.

The likelihood that a specific case will be genetic increases in the following situations:
  • Absence of an environmental cause that would indicate acquired damage.

  • Progression and worsening of the convulsions and/or neurological damage over time.

  • Presence of dystonic, involuntary movements.

  • Presence of more severe mental retardation than expected from the convulsions alone.

  • Absence of signs supporting environmental damage in a brain scan (CT or MRI).

  • Presence of signs indicating a genetic disease on examination of the child or in laboratory and/or scanning tests.

Cerebral hypertension secondary to hydrocephalus and chromosome disorders must be ruled out. It is especially important to rule out metabolic disorders such as leukodystrophies. All these conditions must be investigated by a geneticist and a physical examination carried out. It is important to look for spots on the skin, muscular weakness, changes in the teeth, and other signs, which can indicate a specific syndrome.

Inheritance pattern

In most cases, the cause is not hereditary. In the hereditary types, the risk of recurrence depends on the precise condition - see the table below. Inheritance can be multifactorial or autosomal dominant with incomplete penetrance. In the more severe types, inheritance may be autosomal recessive or mitochondrial.

Penetrance

A significant number of cases are transmitted by autosomal dominant inheritance with incomplete penetrance.

Associated features that can be demonstrated by ultrasound examination

In the classic types of epilepsy, usually there are no defects that can be identified by ultrasound examination during pregnancy. If a specific syndrome is diagnosed, such as a disorder of development of brain structure, tuberous sclerosis, etc., characteristic signs of these syndromes can then be looked for on ultrasound.

What is the risk of recurrence in a subsequent pregnancy?

This depends on which type of epilepsy the patient has. In cases where the cause of the brain damage is environmental, i.e. non-genetic, there is no increased risk of recurrence. In the hereditary cases, the risk of recurrence depends on the specific condition and is in accordance with the inheritance pattern of that condition and the relationship to the patient. In most cases when there is only one case in the family, the risk of recurrence is not high. When there are a number of affected individuals in the family, or there are signs that indicate that this is a genetic syndrome, there may be an increased risk of recurrence.

When there are 2 affected siblings, a hereditary metabolic disease should be suspected. The risk that further children will be affected is 25% in conditions transmitted by autosomal recessive inheritance, and 50% in conditions transmitted by autosomal dominant inheritance.

Molecular genetic information

The disease-causing genes and their locations for the different conditions are shown in the following table:
Type Heredity Location of gene Name of gene Function of gene Characteristic signs
Benign familial neonatal convulsions Autosomal dominant 20q

8q
KCNQ2

KCNQ3
Potassium channels forming electrical voltage gradient Benign convulsions appearing at a few days of age. 10% have residual adult epilepsy. No mental retardation.
Nocturnal frontal lobe epilepsy Autosomal dominant 20q

15q

1p21
CHRNA4

?

CHRNB2
Components A4 and B2 of the nicotinic acetylcholine receptor responsible for calcium permeability. Convulsions appearing in sleep. Starts in childhood and continues to adolescence. No mental retardation.
Generalized epilepsy with febrile seizure plus Autosomal dominant 19q13

2q24



5q31
SCN1B

SCN1A



GABRG2
Sodium channels forming electrical voltage gradient. GABA-A receptor. Febrile convulsions or general convulsions induced by fever. Sometimes partial convulsions.
Progressive myoclonic epilepsy of Unvezzicht Lunborg Autosomal recessive 6q24 EPM2a

Laforin
Tyrosine phosphatase (tyrosine kinase antagonist) Myoclonic convulsions commencing in adolescence.
Familial idiopathic myoclonic epilepsy of infancy Autosomal recessive 16p13 Unknown Unknown Myoclonic convulsions from infancy. No mental retardation.
Severe myoclonic epilepsy of infancy Sporadic - autosomal dominant cases are due to a new mutation 2q24 SCN1A Sodium channel causing electrical voltage gradient. Myoclonic convulsions from infancy, progressing to mental retardation or walking instability.
Juvenile myoclonic epilepsy Multifactorial? Suspected gene on 6p and 15q. Unknown Unknown Convulsions from age 8-26. Myoclonic in the morning.
Idiopathic generalized epilepsy Multifactorial? Suspected gene on chrom-osome 18. Unknown Unknown Convulsions from adolescence, various types.


Diagnostic testing

An examination should be carried out by a geneticist in order to look for a specific genetic syndrome. A blood test should also be done to look for a chromosomal problems, and if necessary specific blood tests to look for metabolic diseases based on the results of the geneticist-s examination. If the clinical presentation indicates that there is a mutation in a specific gene, genetic testing can be done straight away if this is available. Investigation is also possible in the familial cases. It is then possible to examine the location of the gene causing the disease in the specific family by linkage analysis. See information sheet: Indirect testing for genetic markers in a family with one or more patients in the family - when there are a number of different genes that can each cause the disease - not all the genes having been located / identified / mapped - autosomal dominant disease

Carrier testing

This cannot usually be performed, unless there is a specific syndrome whose gene can be tested for. See above in the section on diagnostic testing.

Fetal testing

This cannot usually be performed, unless there is a specific syndrome whose gene can be tested for. See above in the section on diagnostic testing.


What Causes Epilepsy?


 
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