Mutations in PRRT2 responsible for paroxysmal kinesigenic dyskinesias also cause benign familial infantile convulsions.

Paroxysmal kinesigenic dyskinesia (PKD (MIM128000)) is a neurological disorder characterized by recurrent attacks of involuntary movements. Benign familial infantile convulsion (BFIC) is also one of a neurological disorder characterized by clusters of epileptic seizures. The BFIC1 (MIM601764), BFIC2 (MIM605751) and BFIC4 (MIM612627) loci have been mapped to chromosome 19q, 16p and 1p, respectively, while BFIC3 (MIM607745) is caused by mutations in SCN2A on chromosome 2q24. Furthermore, patients with BFIC have been observed in a family concurrently with PKD. Both PKD and BFIC2 are heritable paroxysmal disorders and map to the same region on chromosome 16. Recently, the causative gene of PKD, the protein-rich transmembrane protein 2 (PRRT2), has been detected using whole-exome sequencing. We performed mutation analysis of PRRT2 by direct sequencing in 81 members of 17 families containing 15 PKD families and two BFIC families. Direct sequencing revealed that two mutations, c.649dupC and c.748C>T, were detected in all members of the PKD and BFIC families. Our results suggest that BFIC2 is caused by a truncated mutation that also causes PKD. Thus, PKD and BFIC2 are genetically identical and may cause convulsions and involuntary movements via a similar mechanism.

Echocardiographic and electrocardiographic analyses of patients with severe motor and intellectual disabilities.

Severe motor and intellectual disabilities (SMID) syndrome is a heterogeneous group of disorders with severe physical disabilities and mental retardation. Higher incidence of sudden death is also known in these patients. However, little is known about the cardiovascular features of patients with SMID. We examine the patients with severe motor and intellectual disabilities using echocardiogram and clarify their characterization of ventricular function. We performed electrocardiographic and echocardiographic analyses in SMID patients. In all patients, two-dimensional echocardiography with tissue Doppler analysis in the pulsed Doppler mode was performed. Of 121 patients, 104 patients had abnormal findings: 81 had poor R-wave progression, and 15 patients had low-voltage QRS on ECG. These findings strongly correlated with the degree of physical disability. However, on echocardiography, most patients had LVEF in the normal range, while LV Tei indices were significantly higher (0.43 vs 0.31 cm/s) and left ventricular end-diastolic dimension significantly smaller than healthy controls (P<0.05 for each comparison). Patients had significantly decreased early diastolic tissue Doppler velocities at the lateral mitral (5.3 vs 6.7 cm/s), tricuspid (6.7 vs 9.2 cm/s), and septal (5.9 vs 8.8 cm/s) annuli compared with controls (P<0.05 for each comparison). We show for the first time that SMID patients have low E/Ea ratios on tissue Doppler imaging while LV contractions are normal, suggesting the existence of latent diastolic dysfunction. This may be one of the reasons why the incidence of sudden death is higher in SMID patients.

Paroxysmal kinesigenic choreoathetosis (PKC): confirmation of linkage to 16p11-q21, but unsuccessful detection of mutations among 157 genes at the PKC-critical region in seven PKC families.

Paroxysmal kinesigenic choreoathetosis (PKC) is a paroxysmal movement disorder of unknown cause. Although the PKC-critical region (PKCCR) has been assigned to the pericentromeric region of chromosome 16 by several studies of families from various ethnic backgrounds, the causative gene has not yet been identified. In the present study, we performed linkage and haplotype analysis in four new families with PKC, as well as an intensive polymerase chain reaction (PCR) based mutation analysis in seven families for a total of 1,563 exons from 157 genes mapped around the PKCCR. Consequently, the linkage/haplotype analysis revealed that PKC was assigned to a 24-cM segment between D16S3131 and D16S408, the result confirming the previously defined PKCCR, but being unable to narrow it down. Although the mutation analysis of the 157 genes was unsuccessful at identifying any mutations that were shared by patients from the seven families, two nonsynonymous substitutions, i.e., 6186C>A in exon 3 of SCNN1G and 45842A>G in exon 29 of ITGAL, which were segregated with the disease in Families C and F, respectively, were not observed in more than 400 normal controls. Thus, one of the two genes, SCNN1G and ITGAL, could be causative for PKC, but we were not able to find any other mutations that explain the PKC phenotype.