The clinical spectrum of female epilepsy patients with PCDH19 mutations in a Chinese population.

Mutations in PCDH19, which encodes protocadherin 19, have been identified in epilepsy, mainly in affected females. We summarized the clinical spectrum of female epilepsy patients with PCDH19 mutations in a Chinese population. We screened for PCDH19 mutations in 75 girls diagnosed with Dravet syndrome (DS) without a SCN1A mutation and 29 girls with fever-sensitive and cluster seizures. We identified 11 novel and 7 reported mutations in 21 of 104 probands (20.2%), including 6 (6/75, 8%) DS girls and 15 (15/29, 51.7%) girls with fever-sensitive epilepsy. The mutations were inherited in 9 probands, de novo in 11, and undetermined in the remaining patient. Shared clinical features included early onset seizures (5-18 months), seizures sensitive to fever, focal seizures or generalized tonic-clonic seizures in clusters and brief seizures. Mental retardation was present in 17 probands. Three patients had autistic features. Two of the nine probands with inherited mutations had no family history of epilepsy, one inherited the mutation from her transmitting father and the other inherited from her asymptomatic mother. Our results confirmed that the clinical spectrum of PCDH19 mutations includes female DS patients, epilepsy and mental retardation limited to females, epilepsy with normal development and asymptomatic female carriers.

The SCN1A gene variants and epileptic encephalopathies.

The voltage-gated sodium channels are fundamental units that evoke the action potential in excitable cells such as neurons. These channels are integral membrane proteins typically consisting of one α-subunit, which forms the larger central pore of the channel, and two smaller auxiliary ß-subunits, which modulate the channel functions. Genetic alterations in the SCN1A gene coding for the α-subunit of the neuronal voltage-gated sodium ion channel, type 1 (NaV 1.1), is associated with a spectrum of seizure-related disorders in human, ranging from a relatively milder form of febrile seizures to a more severe epileptic condition known as the Dravet syndrome. Among the epilepsy genes, the SCN1A gene perhaps known to have the largest number of disease-associated alleles. Here we present a meta-analysis on the SCN1A gene variants and provide comprehensive information on epilepsy-associated gene variants, their frequency, the predicted effect on the protein, the ethnicity of the affected along with the inheritance pattern and the associated epileptic phenotype. We also summarize our current understanding on the pathophysiology of the SCN1A gene defects, disease mechanism, genetic modifiers and their clinical and diagnostic relevance.

Four novel SCN1A mutations in Turkish patients with severe myoclonic epilepsy of infancy (SMEI).

Severe myoclonic epilepsy of infancy (SMEI) (OMIM #607208), also known as Dravet syndrome, is a rare genetic disorder characterized by frequent generalized, unilateral clonic or tonic-clonic seizures that begin during the first year of life. Heterozygous de novo mutations in the SCN1A gene, which encodes the neuronal voltage-gated sodium channel α subunit type 1 (Nav1.1), are responsible for Dravet syndrome, with a broad spectrum of mutations and rearrangements having been reported. In this study, the authors present 4 novel mutations and confirm 2 previously identified mutations in the SCN1A gene found in a cohort of Turkish patients with Dravet syndrome. Mutational analysis of other responsible genes, GABRG2 and PCDH19, were unrevealing. The authors' findings add to the known spectrum of mutations responsible for this disease phenotype and once again reinforce our understanding of the allelic heterogeneity of this disease.

Electroclinical and genetic findings in a family with cortical tremor, myoclonus, and epilepsy.

We report a five-generation family showing cortical tremor, myoclonus, and epilepsy, originating from Naples, Italy. Eleven members, aged 24-56 years (mean: 39.2 years), suffered from hand tremor and myoclonus, whereas generalized seizures occurred in six. Electrophysiological study confirmed the presence of cortical reflex myoclonus in all affected members. In addition, giant somatosensory-evoked potential components and enhanced long loop reflex I were found also in three presymptomatic members who manifested hand tremor and myoclonus at upper limbs after 1.5 years of follow-up. Genetic study of the pedigree revealed a significant linkage on chromosome 2p (maximum lod score = 5.9). Further observations are needed to clarify the pathophysiology of this condition.

Juvenile myoclonic epilepsy: disease expression among Indian families.

OBJECTIVES: Juvenile myoclonic epilepsy (JME) is a common, age related, idiopathic generalized epileptic syndrome. We aimed to define the expression of JME in Indian probands and study the occurrence of seizures/epileptic syndromes in their family members. METHODS: We studied 225 JME probands with a uniform protocol. recording the type and frequency of seizures, precipitating factors, EEG data, and family history. Detailed family pedigrees were drawn to include all the 1st- and 2nd-degree relatives of probands. The seizures/epileptic syndromes in relatives examined were classified in a uniform way. RESULTS: The clinical and EEG characteristics of 225 JME probands from India were similar to those reported in probands from different ethnic backgrounds. The incidence of febrile convulsions in probands with JME was similar to that of the general population but was much lower (0.2%) among their relatives. A positive family history of seizures among 1st- or 2nd-degree relatives was noted in 79 of 225 (35%) probands. The risk of relatives being affected as well as their risk of expressing a type of idiopathic generalized epilepsy (IGE) varied as a function of the degree of relation with the probands. CONCLUSIONS: The clinical expression of JME among probands from India is fairly similar to that reported in probands of different ethnic backgrounds. The risk of relatives being affected as well as their risk of expressing a type of IGE (including JME) varies as a function of the degree of relation with the probands. The reduced occurrence of febrile convulsions among the relatives of JME probands probably represents an ascertainment bias. A much larger database of this type should be helpful in understanding the interactions of different genes that are believed to be responsible for some of the inherited human epileptic syndromes like JME and other IGEs.

Allelic heterogeneity of Mediterranean myoclonus and the cystatin B gene.

Mediterranean myoclonus is a progressive myoclonus epilepsy with autosomal recessive inheritance. Another form has been described in Finland, the so-called Baltic myoclonus. Mediterranean myoclonus and Baltic myoclonus are also known as Unverricht-Lundborg disease. Linkage analyses have shown that the genes for both these forms of myoclonus are closely linked to 21q22.3 DNA markers, suggesting that they are caused by mutations at the same locus (EPM1). Recently, two heterozygous mutations were found in the cystatin B gene in patients with Unverricht-Lundborg disease. We report recombinational and linkage disequilibrium mapping of EPM1, and cystatin B gene sequencing, in 14 consanguineous pedigrees with Mediterranean myoclonus. Linkage to 21q22.3 DNA markers was observed in all these families. Haplotype analysis suggests that a common mutation segregates within these pedigrees, and that this mutation is different from the common one responsible for the Finnish form of Unverricht-Lundborg disease. No mutation was found in the exons or splice junctions of the cystatin B gene in the 14 pedigrees.

Unverricht-Lundborg disease: absence of nonallelic genetic heterogeneity.

Unverricht-Lundborg disease is a clinically recognizable form of progressive myoclonus epilepsy. Recently, in several families of both Finnish and Mediterranean extraction segregating Unverricht-Lundborg disease, the gene for this disease was linked to the same region of the long arm of chromosome 21. We performed linkage analysis in eight families, including four of neither Baltic nor Mediterranean origin, using a polymorphic (CA)n repeat marker for the human liver-type 6 phosphofructokinase (PFKL) gene, previously mapped to 21q22.3. No recombinations were observed between the disease phenotype and the PFKL marker and a maximum lod score of 5.63 was obtained. These findings confirm tight linkage between PFKL and the gene for Unverricht-Lundborg disease and strongly suggest a lack of nonallelic genetic heterogeneity of the disease.