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Keywords:

  • Chromosome 22q12;
  • FFEVF;
  • FPEVF;
  • Focal epilepsy;
  • Genetic epilepsy

Summary

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. Disclosure
  8. References
  9. Supporting Information

We aimed to refine the phenotypic spectrum and map the causative gene in two families with familial focal epilepsy with variable foci (FFEVF). A new five-generation Australian FFEVF family (A) underwent electroclinical phenotyping, and the original four-generation Australian FFEVF family (B) (Ann Neurol, 44, 1998, 890) was re-analyzed, including new affected individuals. Mapping studies examined segregation at the chromosome 22q12 FFEVF region. In family B, the original whole genome microsatellite data was reviewed. Five subjects in family A and 10 in family B had FFEVF with predominantly awake attacks and active EEG studies with a different phenotypic picture from other families. In family B, reanalysis excluded the tentative 2q locus reported. Both families mapped to chromosome 22q12. Our results confirm chromosome 22q12 as the solitary locus for FFEVF. Both families show a subtly different phenotype to other published families extending the clinical spectrum of FFEVF.

Familial focal epilepsy with variable foci (FFEVF, previously FPEVF) is an unusual familial epilepsy syndrome characterized by focal seizures arising from different cortical regions in different family members (Scheffer et al., 1998; Xiong et al., 1999; Berkovic et al., 2004; Berg et al., 2010). The original Australian family in whom we first described FFEVF in 1998 showed suggestive mapping to chromosome 2q. Six FFEVF families were later definitively mapped to chromosome 22q12 (Xiong et al., 1999; Callenbach et al., 2003; Berkovic et al., 2004; Morales-Corraliza et al., 2010). The gene has not been identified.

Herein we report a new family with FFEVF that maps to chromosome 22q12. We also rephenotyped the original family including new affected family members and show that it now maps to the chromosome 22q12 locus.

Methods

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. Disclosure
  8. References
  9. Supporting Information

Clinical studies

A five-generation Australian family (A) was recruited. The original four-generation Australian family (B) (Scheffer et al., 1998) was revisited. Both families originated from the United Kingdom. Family members were interviewed using a validated seizure questionnaire (Reutens et al., 1992), and medical records were obtained. Electroencephalography (EEG) and, where appropriate, magnetic resonance imaging (MRI) studies were performed. Seizures were classified according to the ILAE seizure classification (Berg et al., 2010).

Linkage studies

Family A

Linkage analysis was performed for the known chromosome 22q12 FFEVF region using microsatellite markers (genotyped at the Australian Genome Research Facility).

Family B

Following phenotypic review, the original 20 cM spaced whole genome microsatellite data was reanalyzed for chromosome 2q and 22q12 markers. Subsequently, fine-mapping of chromosome 22q12 using 12 microsatellite markers was performed on all available family members including newly affected individuals B-V-9, B-V-10, B-V-11.

Logarithm of odds (LOD) scores for markers spanning the FFEVF region were computed using the LINKAGE package of programs (Lathrop & Lalouel, 1984).

Results

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. Disclosure
  8. References
  9. Supporting Information

Family A

Ten individuals had a history of seizures over five generations (Fig. 1A). Of the nine living family members, five had epilepsies consistent with FFEVF (Table S1A) but four did not. The proband A-IV-19 had left parietotemporal cortical dysplasia and was considered unlikely to have FFEVF. Two family members had febrile seizures. The fourth case (A-III-11) had a single unclassified event with no eyewitness account and was an obligate carrier. The deceased subject A-I-2 was reported to have had seizures but no details were available. Mild intellectual disability was present in the most severely affected family member (A-IV-24). His development was normal prior to seizure onset at 3 years.

image

Figure 1.   Pedigrees of the families A (A) and B (B). The linked chromosome 22q12 haplotype is shown in orange. The arrow indicates the proband. Marker genotypes in brackets are inferred.

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The haplotype on chromosome 22q12 segregated with FFEVF in the family (maximum LOD score 2.38, Table S2). Eleven individuals had the chromosome 22q12 haplotype including five with FFEVF (median onset 7 months, mean 2.8 years, range 3 weeks–10 years), four obligate carriers, and two unaffected subjects (Fig. 1A). The family member with structural epilepsy and the two subjects with febrile seizures did not carry the haplotype.

Family B

Twelve individuals had seizures over four generations (Fig. 1B). Eleven family members had phenotypes consistent with FFEVF. There were three new affected individuals and two previously considered affected were now regarded as unknown or unaffected (Table S1B, Results S1).

With the updated phenotypic analysis, the original whole genome microsatellite data revealed that the chromosome 2q haplotypes no longer segregated with affected status and chromosome 2q was excluded. The data were, however, consistent with linkage to the FFEVF locus on chromosome 22q12 (maximum LOD score 2.94, Table S2). For this analysis, we included fine mapping of the newly recruited family members. Ten individuals had the chromosome 22q12 haplotype including eight with FFEVF (median onset: 9.5 years, mean: 13.5 years, range 10 months–40 years), one unaffected obligate carrier and a 12 year-old boy (B-V-9) with autism spectrum disorder (ASD) who has not yet had seizures. Only individual B-V-11 who had seizures did not carry the haplotype; she was considered a phenocopy as her phenotype could potentially have been part of the FFEVF spectrum. Individual B-V-5 with Panayiotopoulos syndrome did not have the 22q12 haplotype. The haplotype was different from family A indicating that the families were not related (data not shown).

Discussion

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. Disclosure
  8. References
  9. Supporting Information

FFEVF is an unusual but distinctive familial focal epilepsy syndrome. The original Australian FFEVF family (family B) introduced the concept that different focal epilepsies in different family members could result from a dominant gene defect. This was confirmed by the study of six further families with FFEVF (Table 1) and identification of the common chromosome 22q12 locus for which the gene remains unknown.

Table 1.   Clinical features of the published families with FFEVF
PublicationFamily originTotal subjects FFEVFFLETLEPLEOLEMultifocalUnclearPredominantly nocturnal seizuresIED
  1. a According to authors’ diagnostic scheme 2.

  2. b Parietooccipital.

  3. FFEVF, familial focal epilepsy with variable foci; FLE, frontal lobe epilepsy; TLE, temporal lobe epilepsy; PLE, parietal lobe epilepsy; OLE, occipital lobe epilepsy; IED, interictal epileptiform discharge.

Scheffer et al. (1998) This studyAustralian1036100017/9
Xiong et al. (1999) (fam. 22)French-Canadian19a160102MostRelatively inactive
Xiong et al. (1999) (fam. 14)French-Canadian 7a70000MostRelatively inactive
Callenbach et al. (2003) Dutch10 (+2 possible)120025Most9/10
Berkovic et al. (2004) (fam. S)Spanish10 (+3 possible)31000672/5
Berkovic et al. (2004) (fam. Q)French-Canadian 921000631/1
Morales-Corraliza et al. (2010) Spanish 990000010/1
Klein et al. (2012)Australian 5 (+2 possible)0021b2003/5

Our families show the characteristic variable foci of FFEVF with six patients with temporal, three frontal, three parietal, one parietooccipital, and one multifocal epilepsy. Penetrance was also typical between 50% and 80%.

We distinguished the phenotype of the original FFEVF family from subsequent families with FFEVF on the basis of seizures in wakefulness, frequent interictal epileptiform activity on EEG, and lack of the nocturnal frontal lobe epilepsy (NFLE) phenotype (Scheffer et al., 1998; Berkovic et al., 2004). Further phenotyping and linkage analysis of the original FFEVF family is now consistent with the same 22q12 region as the other families and excludes the previously reported suggestive linkage to chromosome 2q. Our data do not narrow the previously reported 22q12 region (3.6 cM, 5.2 Mb) between microsatellite markers D22S1163 and D22S280.

The question remains whether there are two familial patterns within the FFEVF syndrome or if they simply reflect a spectrum of phenotypes that can occur in FFEVF. Families A and B share features that differ from the remaining six families as they have more awake seizures and more active EEG studies (three of five in family A and seven of nine in family B, Table 1). In contrast with other FFEVF families who have individuals with nocturnal frontal lobe seizures (Xiong et al., 1999; Callenbach et al., 2003; Berkovic et al., 2004; Morales-Corraliza et al., 2010), our families can easily be distinguished from autosomal dominant NFLE due to their predominantly diurnal attacks and seizures emanating from regions other than the frontal lobe. However, the occurrence of brief nocturnal seizures in our families cannot be excluded without video-polygraphic recordings, which were not available. The concept of a broader phenotypic spectrum is supported by the Dutch family who had both interictal epileptiform discharges and nocturnal seizures (Callenbach et al., 2003; Table 1). Further clinical and molecular characterization of FFEVF will clarify this question.

For the success of the linkage analysis it is important to minimize the number of phenocopies, that is, individuals who have a phenotype within the FFEVF range not due to the same genetic cause. This is particularly difficult in a disorder with the high phenotypic variability characteristic of FFEVF. Here, and in previous work, challenges in phenotyping included whether children with common focal epilepsies of childhood (B-V-11, B-V-5) had FFEVF. Haplotype analysis has helped to distinguish phenocopies (B-V-11, Berkovic et al., 2004). In addition, the proband of family A (A-IV-19) was readily distinguished from FFEVF as he had focal cortical dysplasia consistent with a structural etiology. Febrile seizures occurred in two individuals in family A. Previous studies of FFEVF have not reported febrile seizures. Moreover, our haplotype analysis suggested that febrile seizures were not part of this familial syndrome.

As FFEVF is characterized by a wide phenotypic spectrum, it can be difficult to distinguish from other focal epilepsy syndromes. For example, a Gypsy family included affected family members with the majority having temporal lobe epilepsy and some family members with extratemporal seizure semiology such that the family could be consistent with FFEVF (Angelicheva et al., 2009). However, in the Gypsy family, clinical and EEG data were often not congruent, and linkage analysis excluded the FFEVF locus on chromosome 22q12, suggesting that chromosome 22q12 FFEVF in the Gypsy family was unlikely (Angelicheva et al., 2009).

Autism spectrum disorders have not previously been considered part of FFEVF. However, two of the three subjects in family B with ASD had seizures, and all three carried the chromosome 22q12 haplotype (B-V-9, B-V-10, B-IV-16). Callenbach et al. (2003) described autistic features in two affected individuals and obsessive compulsive features in another individual with FFEVF. Furthermore, intellectual disability was noted in two affected individuals in family B and in one in family A; in both adult cases, their epilepsy was severe. These observations suggest that ASD and intellectual disability are likely to be part of the phenotypic spectrum of FFEVF; modifying genes may explain these severe phenotypes.

Our findings clarify that chromosome 22q12 is the only known candidate region for FFEVF. Both families display phenotypes that expand the phenotypic spectrum at this locus. Next-generation sequencing may be an appropriate tool to identify the underlying gene mutation. This will enable detection of smaller families with FFEVF, and potentially sporadic cases that currently elude diagnosis because of insufficient family members to display phenotypes that produce a recognizable FFEVF pattern.

Acknowledgments

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. Disclosure
  8. References
  9. Supporting Information

We thank the families for participation in our study and Dr. Kathryn Friend for assistance with calculation of LOD scores. The study was supported by the National Health and Medical Research Council of Australia (Program Grant 628952 to SFB, IES, Australia Fellowship 466671 to SFB, Practitioner Fellowship 1006110 to IES and Training Fellowship 1016715 to SEH) and SA Pathology. KMK was supported by a research fellowship from the Deutsche Forschungsgemeinschaft (KL 2254/1-1) and a scholarship from The University of Melbourne.

Disclosure

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. Disclosure
  8. References
  9. Supporting Information

None of the authors has any conflict of interest to disclose. We confirm that we have read the Journal’s position on issues involved in ethical publication and affirm that this report is consistent with those guidelines.

References

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. Disclosure
  8. References
  9. Supporting Information

Supporting Information

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. Disclosure
  8. References
  9. Supporting Information

Figure S1. EEG examples.

Results S1. Phenotypic review of family B.

Table S1. Clinical features of affected subjects of families A (A) and B (B).

Table S2. LOD scores for families A (A) and B (B).

FilenameFormatSizeDescription
EPI_3585_sm_FigS1.tif1775KSupporting info item
EPI_3585_sm_ResultS1.pdf9KSupporting info item
EPI_3585_sm_TableS1.pdf78KSupporting info item
EPI_3585_sm_TableS2.pdf35KSupporting info item

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