Benign Familial Neonatal Convulsions (BFNC). Benign Sporadic Neonatal Convulsions
Incidence
There are two types of BNC: benign familial neonatal convulsions (BFNC) and benign idiopathic or sporadic neonatal convulsions. In the first one, a genetic fault that causes benign familial neonatal convulsions has been found in some genes, which are part of chromosome number 8 and also chromosome number 20. It is usually autosomal dominant but may be autosomal recessive as well. In the second type, benign idiopathic or sporadic neonatal convulsions, there is no history of convulsions at a similar age in other members of the family. The seizures affect girls and boys equally. Prevalence of the syndrome is currently unknown. Caused by mutation in the potassium voltage-gated channel. KCNQ2 pathogenic variants that result in symptoms on the mild end of the spectrum, specifically benign familial neonatal epilepsy (BFNE), are typically inherited in an autosomal dominant fashion, meaning that one or the other parent has the same variant. In such cases, there is often a family history of neonatal seizures that spontaneously resolved.
Clinical Characteristics
Benign familial neonatal seizures (BFNS) is a rare epilepsy of the newborn characterized by partial or generalized seizures, which occur during wakefulness and/or sleep. The seizures can appear in different forms. An arm or leg stiffens and then jerks rhythmically (clonic seizure), the head turns to one side and then jerks a few times, which can be followed by a clonic seizure affecting either side of the body, both arms or legs, or all four limbs may jerk at the same time. There may be repeated cycling or punching movements of the legs or arms or finally but rarely, the whole body goes stiff and then all four limbs jerk (‘tonic-clonic’ seizure). Most seizures last less than two minutes. The seizures are more likely to happen when the baby is sleepy or has just woken from sleep. The babies are otherwise normal and will have been feeding and behaving normally before the seizures started. Their birth usually have been normal. Seizures typically start in the first days of life (between the 3rd to 5th day) and remit spontaneously by approximately 4 months of age. However, about 10 to 15% of patients have febrile or afebrile seizures later in childhood. Seizures observed in these newborns are brief and of a mixed type, starting with tonic posture, apnea, and often progressing to clonic movements and motor automatisms. The neonates are neurologically normal and neurocognitive development is usually normal. Electroclinical events are not specific and BNFS remains a diagnosis of exclusion. It is considered an epileptic syndrome. We should remember that there are other causes for seizures and other epilepsy syndromes that might also start in the neonatal period. These can include low levels of glucose, calcium or magnesium in the blood, infections or abnormalities in the brain. Babies who have benign familial neonatal convulsions or benign idiopathic or sporadic neonatal convulsions can be given the full range of immunisations, including mumps, measles and rubella. Individuals with BFNE are typically otherwise normal and do not have any learning problems or other symptoms.
Precipitants
The seizures are more likely to happen when the baby is sleepy or has just woken from sleep.
Provocation Tests
None. It is a diagnosis of exclusion.
Diagnostic Procedures
It is a clinical diagnosis. Seizures that start around the fifth day after birth in otherwise normal babies are important clues as to the correct diagnosis. Results of tests such as blood tests, electroencephalogram (EEG) and brain computed tomography [CT] or magnetic resonance imaging [MRI]) are usually normal. It is a diagnosis of exclusion. KCNQ2 variants can only be identified by genetic testing. Targeted testing of the KCNQ2 gene specifically is the most direct method of testing an individual when there is a high degree of confidence that a variant in the KCNQ2 gene is likely to be the underlying cause, but this form of testing is being undertaken less commonly over time. Epilepsy gene panels, which involve testing of multiple epilepsy-associated genes, and whole exome sequencing (WES) also detect KCNQ2 variants and are being used more commonly, including rapid testing with these methods applied in the Neonatal ICU setting in order to detect KCNQ2 and other variants.