A novel splicing mutation in KCNQ2 in a multigenerational family with BFNC followed for 25 years

PURPOSE

A large multigenerational family with benign familial neonatal convulsions (BFNC) was revisited to identify the disease-causing mutation and to assess long-term outcome.

METHODS

We supplemented the original data with recent clinical and neurophysiologic data on patients and first-degree relatives, including information on seizure recurrence. We conducted linkage analysis at the EBN1 and EBN2 loci, followed by mutation analysis of KCNQ2. We evaluated the qualitative effect of the KCNQ2 mutation at the messenger RNA (mRNA) level by using reverse-transcribed total RNA isolated from leukocytes.

RESULTS

Thirteen relatives had a history of neonatal convulsions, 11 of whom showed remission within 2 months. One patient showed an atypical course of neonatal convulsions, developing photosensitive myoclonic epilepsy at age 13 years. We found suggestive linkage of the BFNC phenotype to the 20q13-EBN1 locus (lod score, 2.03) and an intronic mutation IVS14-6 C>A in KCNQ2 segregating with the trait in all affected members, but absent in 100 unrelated control subjects. This mutation creates a new, preferentially used, splice site. Alternative splicing adds 4 nt containing a premature stop codon to the transcript, resulting in a truncated protein after position R588.

CONCLUSIONS

We detected and characterized a novel splicing mutation in the brain-specific KCNQ2 gene by using easily accessible blood leukocytes. Aberrant splicing cosegregates with BFNC but not with photosensitivity.

Prevalence of positive anticardiolipin antibody in benign infantile convulsion

We report six anticardiolipin antibody (aCL)-positive cases among 18 children with epilepsy showing various seizure types in our initial study. These six cases revealed normal coagulation tests. As three of these six cases involved benign infantile convulsion (BIC), we further investigated the high frequency of positive aCL-Immunoglobulin (Ig) G in BIC in our subsequent study of nine cases that included three cases from the previous study and an additional six BIC cases followed and/or diagnosed by co-author (T.K.). As a result, eight of nine BIC cases were positive for aCL-IgG and the values of aCL-IgG decreased over long-term observation in three of these cases. The frequency of positivity for aCL-IgG in BIC was obviously higher than that of controls. Based on these results, we suggest that some immunological responses may be responsible for the pathogenesis of BIC.

Clinical pharmacokinetics of phenobarbital in neonates

Demographic and clinical pharmacokinetic data collected from term and preterm neonates who were treated with intravenous phenobarbital have been analysed to evaluate the role of patient characteristics in pharmacokinetic parameters. Significant relationships between total body weight (TBW) or body surface area (BSA) and volume of distribution (Vd) and total body clearance (CL) were found. Coefficients of determination were: 0.55 and 0.59 for Vd, and 0.76 and 0.72 for CL against TBW and BSA, respectively. In addition, significant relationships between height of the infants and volume of distribution of phenobarbital and total body clearance were observed. Coefficients of determination were 0.58 for Vd and 0.56 for CL. A weaker but significant correlation existed between gestational age and Vd or CL of phenobarbital. Coefficients of determination were 0.43 and 0.64, respectively. There was no correlation between volume of distribution per kg body weight or total body clearance per kg body weight and any patient parameter investigated. However, these latter pharmacokinetic parameters tended to decrease with increasing gestational age and height of the neonates. The results obtained were used to develop new loading and maintenance doses for phenobarbital in neonates based on total body weight and body surface area and based on height and gestational age for cases that weight is not available.