Chromosome abnormalities and epilepsy

Genetic basis of pediatric epilepsy syndromes

Childhood epilepsy affects ~0.5-1% in the general population worldwide. Early-onset epileptic encephalopathies are considered to be severe neurological disorders, which lead to impaired motor, cognitive, and sensory development due to recurrence of seizures. Many of the observed epilepsy phenotypes are associated with specific chromosomal imbalances and thus display gene dosage effects, and also specific mutations of a variety of genes ranging from ion channels to transcription factors. High throughput sequencing technologies and whole exome sequencing have led to the recognition of several new candidate genes with a possible role in the pathogenesis of epileptic encephalopathies. The mutations causing channelopathies can be either a gain or a loss of ion channel function and contribute to the pathogenesis of epilepsy syndrome. Nearly 300 mutations of SCN1A gene coding for the Nav1.1 channel protein have been identified that contribute to the pathology of epilepsy. Besides Na, potassium and calcium channels are also implicated in epileptic encephalopathies. Therapeutic management of epileptic encephalopathies has been challenging as the majority of the medications are not efficient and often have many undesirable side effects. A better understanding of the molecular nature of epilepsy in an individual is important to design a personalized medication, considering the number of possible genetic mutations that can contribute to epileptic encephalopathies.

Electroclinical findings in four patients with karyotype 47,XYY

47,XYY karyotype is a Y chromosome aneuploidy characterized by an extra copy of the Y chromosome in each of the male cells, with an incidence of 1/1000 males. Most studies about 47,XYY have focused on growth, cognitive development, academic performance, behavioural problems, speech and language skills and neuromuscular status. Up-to-date reports on seizures and EEG characteristics concerning 47,XYY men have been sporadic and poorly detailed. The aim of this study is to describe the particular electroclinical patterns in a group of four subjects with 47,XYY karyotype. We performed neurological examinations, psychometric tests, brain MRIs, prolonged EEG recordings during awake and sleep on four unselected males 47,XYY. All four patients presented various degrees of neuropsychological impairment. An incidence of familial antecedents for epilepsy was confirmed by three families. When present, seizures were very similar to that of benign epilepsy with central-temporal spikes, (BECTS), for age of onset, clinical picture, evolution and good response to antiepileptic drugs. EEG recordings in all four subjects showed normal background activity and sleep organization, particular focal spikes and sharp-waves localized mostly over the vertex and/or central-temporal regions, which increased during sleep. In our opinion, these 47,XYY patients present a particular electroclinical pattern.

Epilepsy and chromosomal abnormalities

Background

Many chromosomal abnormalities are associated with Central Nervous System (CNS) malformations and other neurological alterations, among which seizures and epilepsy. Some of these show a peculiar epileptic and EEG pattern. We describe some epileptic syndromes frequently reported in chromosomal disorders.

Methods

Detailed clinical assessment, electrophysiological studies, survey of the literature.

Results

In some of these congenital syndromes the clinical presentation and EEG anomalies seems to be quite typical, in others the manifestations appear aspecific and no strictly linked with the chromosomal imbalance. The onset of seizures is often during the neonatal period of the infancy.

Conclusions

A better characterization of the electro clinical patterns associated with specific chromosomal aberrations could give us a valuable key in the identification of epilepsy susceptibility of some chromosomal loci, using the new advances in molecular cytogenetics techniques - such as fluorescent in situ hybridization (FISH), subtelomeric analysis and CGH (comparative genomic hybridization) microarray. However further studies are needed to understand the mechanism of epilepsy associated with chromosomal abnormalities.

A de novo 11p12-p15.4 duplication in a patient with pharmacoresistant epilepsy, mental retardation, and dysmorphisms

We report a 22-year-old male patient with pharmacoresistant epilepsy, mental retardation and dysmorphisms. Standard cytogenetic analysis revealed a de novo interstitial duplication of the short arm of chromosome 11 (11p). High density array-CGH analysis showed that the rearrangement spans about 35Mb on chromosome 11p12-p15.4. Duplications of 11p are rare and usually involve the distal part of the chromosome arm (11p15), being not associated with epilepsy, whereas our patient showed a unique epileptic phenotype associated with mental retardation and dysmorphic features. The role of some rearranged genes in epilepsy pathogenesis in this patient is also discussed.

Neurological aspects of hyperinsulinism-hyperammonaemia syndrome

Hyperinsulinism-hyperammonaemia syndrome (HHS) is a rare cause of congenital hyperinsulinism, due to missense mutations in the GLUD1 gene, resulting in glutamate dehydrogenase (GDH) overactivity. The aim of this study was to document the spectrum of neurological disturbances associated with HHS and to identify possible phenotype-genotype correlations. We retrospectively analyzed the neurological outcomes of 22 consecutive patients (12 males, 10 females) aged from 18 months to 40 years and diagnosed with HHS. We analyzed demographic and clinical features and neuroradiological, biochemical, and genetic findings. Fourteen patients had childhood-onset epilepsy. Learning disability was found in 17 patients. Two patients had pyramidal involvement and one had generalized dystonia. Seizures were observed in 11 of 19 patients with documented GLUD1 mutations, and nine of these 11 patients had a mutation in the guanosine triphosphate (GTP) binding site. Our data demonstrate that neurological disorders in HHS are more frequent than previously thought and might suggest that mutations in the GTP binding site of GDH could be associated with more frequent epilepsy.

Partial monosomy Xq(Xq23 --> qter) and trisomy 4p(4p15.33 --> pter) in a woman with intractable focal epilepsy, borderline intellectual functioning, and dysmorphic features

Studies of epilepsy associated with chromosomal abnormalities may provide information about clinical and EEG phenotypes and possibly to identify new epilepsy genes. We describe a female patient with intractable focal epilepsy, borderline intellectual functioning, and facial dysmorphisms, in whom genetic study (i.e., karyotype and array-CGH analysis) revealed a distal trisomy 4p and distal monosomy Xq. Although any genetic hypothesis remains speculative, several genes are located in the 4p chromosome segment involved in the rearrangement, some of which may be related to epilepsy.

Myoclonic absence epilepsy with photosensitivity and a gain of function mutation in glutamate dehydrogenase

Activating mutations in glutamate dehydrogenase (GDH), de novo or dominantly inherited, are responsible for the hyperinsulinism/hyperammonemia (HI/HA) syndrome. Epilepsy has been frequently reported in association with mutations in GDH, but the epilepsy phenotype has not been clearly determined. Here, we describe a family with a dominantly inherited mutation in GDH. The mother, brother and both sisters had myoclonic absence seizures, but only the mother and one sister had the complete HI/HA pattern. For the two sisters with myoclonic absences, epilepsy started during the second year of life while the brother, it started at 6 years. All 3 children showed the same EEG pattern characterized by photosensitive generalized and irregular spike-wave discharges and runs of multiple spikes. The mother's EEG recordings were normal without photosensitivity. Magnetic resonance imaging (MRI) and spectroscopy (MRS) were normal. A direct effect of the GDH mutation, perhaps in combination with recurrent hypoglycemia and chronic hyperammonemia could provide a pathophysiological explanation for the epilepsy observed in this syndrome and these are discussed.

Photoparoxysmal responses in children with chromosomal aberrations

Electroencephalographic (EEG) anomalies and epilepsy are commonly observed in the clinical picture of patients with chromosomal aberrations. However, no investigations have been performed on the relationship between chromosomal disorders and photoparoxysmal response (PPR). In this study, we evaluate the characteristics of PPRs elicited with intermittent photic stimulation during a routine electroencephalogram in children affected by chromosomal anomalies and correlated this with the clinical profile of the child. A review of the literature has also been performed. PPRs occurred in 14% (4/28) of patients. PPRs were brief (<less 5s), self-limited, elicited by several series of flashes, with an onset latency between 2 and 9s, and scarcely controlled by anticonvulsants. Although further studies are needed to confirm the present data, our observations and the review of the literature suggest that patients carrying chromosomal anomalies might have a higher risk for photosensitivity when compared to the normal population. In these patients, PPR might occur early in life, persist into adulthood, and is commonly inscribed in more polymorphic electroclinical patterns.

6q Terminal Deletion Syndrome Associated with a Distinctive EEG and Clinical Pattern: A Report of Five Cases

PURPOSE

Mental retardation, facial dysmorphisms, and neurologic and brain abnormalities are features of 6q terminal deletions. Epilepsy is frequently associated with this chromosome abnormality, but electroclinical findings are not well delineated. We report five unrelated patients with 6q terminal deletions and a peculiar clinical, EEG, and neuroradiologic picture of epilepsy, mental retardation, and colpocephaly.

METHODS

These three male and two female patients underwent general and neurologic examinations, repeated awake and sleep EEGs, and brain magnetic resonance imaging (MRI). A cytogenetic study and fluorescent in situ hybridization (FISH) with chromosome-specific subtelomeric probes were carried out in all cases.

RESULTS

All subjects had seizures characterized by vomiting, cyanosis, and head and eye version, with and without loss of consciousness. In four cases, EEGs showed posterior spike-and-wave complexes, which were activated by sleep. No patient had status epilepticus or prolonged seizures. Brain MRI revealed colpocephaly and dysgenesis of the corpus callosum and brainstem in four patients; three of them also had hypertrophic massa intermedia. FISH analysis revealed a 6q terminal deletion in all patients, which ranged between 9 Mb (cases 2 and 3) and 16 Mb (case 4).

CONCLUSIONS

We suggest that epilepsy associated with 6q terminal deletions is a new entity. Patients with dysmorphic features associated with focal occipital epilepsy, colpocephaly, and dysgenesis of the corpus callosum, thalami, and brainstem should be considered candidates for testing for 6q subtelomere deletions.

Chromosome 18 aberrations and epilepsy: a review

Epilepsy is commonly observed in patients with chromosomal aberrations. We evaluated epilepsy and electroencephalographic (EEG) features in a group of patients carrying aberrations of chromosome 18. Fourteen patients were recruited: five with an 18p deletion syndrome (18pDS); six with an 18q deletion syndrome (18qDS); two with trisomy 18p syndrome; and one with a 45,XY,t(17-18) (cen-q11.2) karyotype. Patients with 18pDS had neither epilepsy nor EEG anomalies; four patients with 18qDS had epilepsy with partial seizures occurring during infancy or early childhood. Partial seizures were also present in both patients with trisomy 18p. By contrast, mixed seizures were observed in the patient carrying a translocation between chromosomes 17 and 18. Our data and a re-evaluation of the literature suggest that epilepsy is infrequent in patients with 18pDS. Conversely, partial seizures and focal EEG anomalies may be observed in those with patients with 18qDS. Our observations suggest that the haplo-insufficiency of genes located on the long arm of chromosome 18 is more likely to be associated with epilepsy, than is haplo-insufficiency of genes located on the short arm. While further EEG/clinical investigations are needed to validate these observations, this study indicates a possible relationship between chromosome 18 genes and epilepsy.

Epilepsy in chromosomal abnormalities: an Italian sample

Epilepsy is common in chromosomal abnormalities, but systematic studies are scanty. We describe an Italian sample of patients with chromosomopathies to establish epilepsy occurrence and clinical electroencephalographic (EEG) features. Forty-five patients with different types of chromosomal abnormalities were analyzed to examine different variables in patients with epilepsy (group 1) and without (group 2) and to compare the types of epilepsy in our cases with respect to a nonselected sample of Italian people with epilepsy. Epilepsy occurred in 51.1% (group 1) of cases and prevailed in autosomal abnormalities but without a statistical significance (P > .05). There was a prevalence of EEG paroxysmal abnormalities in group 1 (P < .0001); continuous spike-waves during sleep were observed in three cases. Profound mental retardation prevailed in group 1 (P < .001) and mild mental retardation in group 2 (P < .05). Generalized epilepsies prevailed significantly (P < .00001). A high-resolution karyotype should be undertaken in all patients with epilepsy presenting with mental retardation when an obvious etiology is not available.

Multi-institutional study on the correlation between chromosomal abnormalities and epilepsy

While there is an abundance of literature describing the association of chromosome aberrations with epilepsy, only a few refer to the detailed features of epilepsy. It is important to investigate the associations between specific chromosome abnormalities and features of epilepsy to identify genes involved in epilepsy and treat them more effectively. We investigated the correlation between specific chromosome aberrations and epilepsy by sending questionnaires to the members of Kyoto Multi-institutional Study Group of Pediatric Neurology. Seventy-six patients were collected from 10 institutions. Chromosome abnormalities included: Down syndrome (n = 19); Angelman syndrome (n = 8); Prader-Willi syndrome (n = 4); 4p- syndrome (n = 3); 1q- syndrome (n = 2); 5p- syndrome (n = 2); Miller-Dieker syndrome (n = 2); 18q- syndrome; (n = 2); Klinefelter syndrome; (n = 2); and 32 other individual chromosomal aberrations. Overall, the severity of mental retardation correlated with the severity of epilepsy. We could abstract characteristic features of epilepsy in some syndromes. In Angelman and Prader-Willi syndromes, febrile seizures occurred frequently, the onset of epilepsy was in early childhood and seizure phenotype was multiple. Paroxysmal discharge of the occipital region and diffuse high voltage slow wave on electroencephalography were characteristic in Angelman syndrome. In Down syndrome, West syndrome and focal epilepsy were common and the prognosis of epilepsy in West syndrome with Down syndrome was good. In 4p- syndrome, febrile seizures were often seen, and unilateral or generalized clonic or tonic-clonic status epilepticus were characteristic. For the other chromosomal aberrations investigated here, the patient numbers were too small to abstract common features of epilepsy.

Epilepsy and electroencephalographic findings in pericentric inversion of chromosome 12

Epilepsy, together with mental retardation, represents a common manifestation of chromosomal aberrations. Specific electroencephalographic (EEG) and epileptic patterns have been described in several chromosomal disorders, such as Angelman's syndrome, Miller-Dieker syndrome, Wolf-Hirschhorn syndrome, and ring 20 syndrome. A peculiar electroclinical pattern has also been identified in trisomy 12p syndrome. We report three patients with a pericentric inversion of chromosome 12, with breakpoints localized to p11-q13 and affected by epilepsy or EEG anomalies. Two suffered from epilepsy, which, in the clinical course, was mainly characterized by complex partial seizures with a semiology related to the temporal lobe. In one patient, myoclonic absences, head drop, and massive jerky attacks were also present. In both patients, generalized 3 Hz bursts were registered, together with multifocal and focal paroxysmal activity, which were most prominent in the temporoparietal and temporal areas, respectively. In the other patient, who had no epilepsy, EEG showed bioccipital paroxysmal activity. In all patients, the clinical picture was characterized by the presence of moderate mental retardation and behavioral disorders. The incidence of epilepsy or EEG anomalies among patients with a pericentric inversion of chromosome 12 remains to be ascertained. However, the present study confirms that chromosome 12 anomalies can be associated with epilepsy. Although myoclonic absence-like episodes can occasionally be part of the epileptic phenotype, the electroclinical pattern in pericentric inversion of chromosome 12 seems to be more polymorphic when compared with that observed in trisomy 12p syndrome.

Electroencephalographic and Epileptic Patterns in X Chromosome Anomalies

Although epilepsy and mental retardation are commonly observed in individuals with chromosomal aberrations, the identification of EEG/epileptic profiles in those with specific chromosome anomalies remains difficult. A few syndromes seem to show peculiar clinical and EEG associations. The authors report an electroclinical investigation on a group of patients carrying X chromosome anomalies: 16 patients with Turner's syndrome, 17 with Klinefelter's syndrome, 1 with an X-autosomal rearrangement, 2 with Xq isochromosome [Xq(i)], and 7 with triple X syndrome. Epilepsy and/or EEG anomalies were found in three of the patients with Klinefelter's syndrome, in one patient with an X-autosomal rearrangement, and in five of those with triple X syndrome. No epilepsy or EEG anomalies were detected in the other patients. Epilepsy may be associated with Klinefelter's syndrome. In addition, the authors found that an electroclinical pattern, represented by paroxysmal activity in the posterior regions (temporo-parieto-occipital areas) with complex partial seizures and easily controlled by antiepileptic drugs, may be present in patients with triple X syndrome. In contrast, gross X-autosomal rearrangements are associated with polymorphic EEG/epileptic findings. Although further studies are needed to validate these observations, they clearly confirm the strict relationship between X chromosome anomalies and epilepsy.