Sarenur Gokben

Whole-exome sequencing identifies recessive WDR62 mutations in severe brain malformations

The development of the human cerebral cortex is an orchestrated process involving the generation of neural progenitors in the periventricular germinal zones, cell proliferation characterized by symmetric and asymmetric mitoses, followed by migration of post-mitotic neurons to their final destinations in six highly ordered, functionally specialized layers. An understanding of the molecular mechanisms guiding these intricate processes is in its infancy, substantially driven by the discovery of rare mutations that cause malformations of cortical development. Mapping of disease loci in putative Mendelian forms of malformations of cortical development has been hindered by marked locus heterogeneity, small kindred sizes and diagnostic classifications that may not reflect molecular pathogenesis. Here we demonstrate the use of whole-exome sequencing to overcome these obstacles by identifying recessive mutations in WD repeat domain 62 (WDR62) as the cause of a wide spectrum of severe cerebral cortical malformations including microcephaly, pachygyria with cortical thickening as well as hypoplasia of the corpus callosum. Some patients with mutations in WDR62 had evidence of additional abnormalities including lissencephaly, schizencephaly, polymicrogyria and, in one instance, cerebellar hypoplasia, all traits traditionally regarded as distinct entities. In mice and humans, WDR62 transcripts and protein are enriched in neural progenitors within the ventricular and subventricular zones. Expression of WDR62 in the neocortex is transient, spanning the period of embryonic neurogenesis. Unlike other known microcephaly genes, WDR62 does not apparently associate with centrosomes and is predominantly nuclear in localization. These findings unify previously disparate aspects of cerebral cortical development and highlight the use of whole-exome sequencing to identify disease loci in settings in which traditional methods have proved challenging.

Mutations in CLN7/MFSD8 are a common cause of variant late-infantile neuronal ceroid lipofuscinosis

The neuronal ceroid lipofuscinoses (NCLs), the most common neurodegenerative disorders of childhood, are characterized by the accumulation of autofluorescent storage material mainly in neurons. Although clinically rather uniform, variant late-infantile onset NCL (vLINCL) is genetically heterogeneous with four major underlying genes identified so far. We evaluated the genetic background underlying vLINCL in 119 patients, and specifically analysed the recently reported CLN7/MFSD8 gene for mutations in 80 patients. Clinical data were collected from the CLN7/MFSD8 mutation positive patients. Eight novel CLN7/MFSD8 mutations and seven novel mutations in the CLN1/PPT1, CLN2/TPP1, CLN5, CLN6 and CLN8 genes were identified in patients of various ethnic origins. A significant group of Roma patients originating from the former Czechoslovakia was shown to bear the c.881C>A (p.Thr294Lys) mutation in CLN7/MFSD8, possibly due to a founder effect. With one exception, the CLN7/MFSD8 mutation positive patients present a phenotype indistinguishable from the other vLINCL forms. In one patient with an in-frame amino acid substitution mutation in CLN7/MFSD8, the disease onset was later and the disease course less aggressive than in variant late-infantile NCL. Our findings raise the total number of CLN7/MFSD8 mutations to 14 with the majority of families having private mutations. Our study confirms that CLN7/MFSD8 defects are not restricted to the Turkish population, as initially anticipated, but are a relatively common cause of NCL in different populations. CLN7/MFSD8 should be considered a diagnostic alternative not only in variant late-infantile but also later onset NCL forms with a more protracted disease course. A significant number of NCL patients in Turkey exist, in which the underlying genetic defect remains to be determined.

Correlative value of magnetic resonance imaging for neurodevelopmental outcome in periventricular leukomalacia

The aim of this study was to evaluate the correlative value of magnetic resonance imaging (MRI) in children with periventricular leukomalacia (PVL) for neurodevelopmental outcome. MRI examinations of 89 children (46 males, 43 females) with PVL (median age 4y, range 1 to 14y) were reevaluated. PVL was graded as follows: grade I, unilateral or bilateral areas of periventricular hyperintensity (1–3); grade II, hyperintensity more than 3; grade III, hyperintense lesions more than 3 and ventricular wall irregularity; grade IV, diffuse PVL and ventricular dilatation. Localizations of PVL and brain abnormalities associated with PVL were also noted. Assignment to PVL grades on MRI was as follows: PVL I (n=22), PVL II (n=18), PVL III (n=30), and PVL IV (n=19). Cerebral palsy was slightly less common in children with PVL I and II compared with PVL III to IV. Motor function was normal in 50% of children with PVL grade I, but severely impaired in 73.7% of children with PVL grade IV. Results of visual function were normal in all with PVL I, but pathological in 42.1% of patients with PVL IV. Developmental tests were appropriate for age in 75% of patients with PVL I, but significantly delayed in all patients with PVL IV. Thinning of the corpus callosum and presence of cortical atrophy were also correlated with neurological outcome. Significant risk factors associated with developmental delay were asphyxia at birth (odds ratio [OR] 4.3), PVL localization numbers over 3 (OR 4.4), PVL III to IV (OR 15), thinning of corpus callosum, and cortical atrophy.

Bone Mineral Status in Pediatric Outpatients on Antiepileptic Drug Monotherapy

Drug-induced osteopenia has been reported in institutionalized children on chronic antiepileptic drug therapy. The aim of this study was to assess longitudinally bone mineral status in pediatric outpatients on antiepileptic drug monotherapy. The study group consisted of 30 ambulatory children on a normal diet: 15 on valproic acid, 11 on carbamazepine, and 4 on phenobarbital monotherapy. Bone mineral density, serum active vitamin D (1,25-dihydroxyvitamin D), and certain biochemical markers of bone formation (calcium, phosphorus, alkaline phosphatase, intact parathyroid hormone, osteocalcin, calcitonin, and urinary calcium to serum creatinine and urinary phosphorus to serum creatinine ratios) were studied at the beginning of antiepileptic drug monotherapy and at the end of 2 years of treatment. Age- and sex-specific Z-scores of bone mineral density were measured at anterior-posterior L2—L4 by dual-energy x-ray absorptiometry. Drug-induced osteopenia was defined in only two patients (one on carbamazepine and the other on phenobarbital monotherapy), with Z-scores of bone mineral density less than —1.5. Serum levels of active vitamin D and biochemical markers were not significantly correlated with the Z-scores of bone mineral density. We detected a frequency of antiepileptic drug—induced osteopenia of 6.7% in pediatric outpatients after 2 years of monotherapy. However, osteopenia was not attributed to a defect in serum active vitamin D production owing to hyperparathyroidism in children on antiepileptic drug monotherapy. ( J Child Neurol2006;21:411—414; DOI 10.2310/7010.2006.00066).

Subclinical Neurological Abnormalities in Children With Celiac Disease Receiving a Gluten-free Diet

Objectives: Because clinically evident manifestations are frequent in adults with celiac disease (CD), we aimed to investigate whether early neurological abnormalities may be detected in children with CD. Methods: Electroencephalography, electromyography, and somatosensory evoked potentials were performed in children with CD receiving a gluten-free diet. Results: The neurophysiological tests revealed subclinical neurological abnormalities associated with CD in 3 (11%) of 27 children: 2 had peripheral polyneuropathy documented with electromyography, and 1 had prolonged latencies in somatosensory evoked potential. Magnetic resonance imaging showed abnormalities in 2 (7.4%) of children: pontine demyelinization in 1 and cortical atrophy in the other. Conclusions: Because the rate of neurological problems is increased in children with CD, neurological abnormalities should be carefully investigated early after the diagnosis of CD is made.

Neuropsychologic Impairment in Children With Rolandic Epilepsy

Although patients with benign childhood epilepsy with centrotemporal spikes exhibit normal intelligence, they frequently display neuropsychologic abnormalities. Thirty-five patients with rolandic epilepsy were included in this study. They were divided into three subgroups. Group I comprised patients with rolandic focus who were not receiving treatment. Group II comprised patients with rolandic focus who were receiving treatment. Group III comprised patients who demonstrated improved foci and were not receiving treatment. The control group comprised 16 children who were similar to patients in terms of age, sex, and sociocultural level. All children underwent standardized neuropsychologic testing, including the Wechsler Intelligence Scale for Children-Revised subtests, Bender Gestalt Test, Stroop Test, Visual Aural Digit Span, Reading and Writing Performance, and Dichotic Listening Test. Patients exhibited significantly impaired visuomotor and reading ability and attention to verbal stimuli compared with control subjects. Reading disability persisted in patients in remission from seizures and epileptic discharges. Contrary to the presumed benign nature of rolandic epilepsy, this disorder may cause learning disabilities. Therefore, patients must be followed longitudinally to identify any learning problems.

Convulsive status epilepticus in children: Etiology, treatment protocol and outcome

This study aimed to determine the etiology, treatment protocol and outcome of convulsive status epilepticus (SE) in children. An institutional treatment protocol using benzodiazepines (diazepam and midazolam) was assessed in a retrospective case study. The treatment protocol (Ege Pediatric Status Epilepticus Protocol or EPSEP) was developed based on an operational definition of pediatric SE according to the duration of seizure activity. Pediatric SE is divided into three categories: initial SE (20-30 min), established SE (30-60 min) and refractory SE (>60 min). Eight (30%) of the studied episodes were initial SE, 10 (37%) were established SE, and 9 (33%) were refractory SE. With respect to the etiological spectrum of SE, 11 (40%) children had meningitis or encephalitis. Febrile SE was identified in 7 (26%) patients. Only 2 episodes of initial SE (7.5%) were controlled with first step of the protocol (two concomitant-doses of rectal diazepam). Midazolam bolus and infusions (up to 1.2 μg/kg/min) were used to treat 22 episodes of SE (9 refractory SE, 10 established SE and 3 initial SE). Complete arrest of convulsive SE was achieved in 21 of 22 (95%) episodes with midazolam infusion. We concluded that the combined use of benzodiazepines (diazepam+midazolam) was safe and effective in the treatment of convulsive SE in children.

Febrile Seizures: Interleukin 1β and Interleukin-1 Receptor Antagonist Polymorphisms

In order to investigate the association between IL-1beta -511 C-->T and IL-1 receptor antagonist intron 2 variable tandem repeat polymorphisms, and febrile seizures in children, 90 children (mean age, 19.7 +/- 11.2 months) diagnosed with febrile seizure and 106 healthy controls (mean age, 14.2 +/- 3.6 months) with no seizure or neurologic events were included in the study. The polymorphisms were analyzed using restriction fragment length polymorphism and agarose gel electrophoresis methods. In the patient group, the frequencies of IL-1beta genotypes CC, CT, and TT were 24.4%, 52.2%, and 23.3%, respectively, compared with 38.7%, 50.95%, and 10.4%, respectively, in the control group. The TT genotype was significantly more common in the patient group than in the control group (P = 0.044), and the T allele frequency was significantly higher in the patient group (0.50 vs 0.36, P = 0.040). Among the three genotypes (RN1/1, RN1/2, and RN2/2) of the IL receptor antagonist gene variable tandem repeat polymorphisms, the frequency of both the RN2/2 genotype and the RN2 allele were significantly higher in the patient group (P = 0.007). Also RN2 allele frequency was found higher in patient group than controls (0.29 vs 0.15, P = 0.020). IL-1beta -511 and IL-1 receptor antagonist intron 2 variable tandem repeat polymorphisms may be involved in susceptibility to febrile convulsions in children.

Novel mutations consolidate KCTD7 as a progressive myoclonus epilepsy gene

Background The progressive myoclonus epilepsies (PMEs) comprise a group of clinically and genetically heterogeneous disorders characterised by myoclonus, epilepsy, and neurological deterioration. This study aimed to identify the underlying gene(s) in childhood onset PME patients with unknown molecular genetic background. Methods Homozygosity mapping was applied on genome-wide single nucleotide polymorphism data of 18 Turkish patients. The potassium channel tetramerisation domain-containing 7 (KCTD7) gene, previously associated with PME in a single inbred family, was screened for mutations. The spatiotemporal expression of KCTD7 was assessed in cellular cultures and mouse brain tissue. Results Overlapping homozygosity in 8/18 patients defined a 1.5 Mb segment on 7q11.21 as the major candidate locus. Screening of the positional candidate gene KCTD7 revealed homozygous missense mutations in two of the eight cases. Screening of KCTD7 in a further 132 PME patients revealed four additional mutations (two missense, one in-frame deletion, and one frameshift-causing) in five families. Eight patients presented with myoclonus and epilepsy and one with ataxia, the mean age of onset being 19 months. Within 2 years after onset, progressive loss of mental and motor skills ensued leading to severe dementia and motor handicap. KCTD7 showed cytosolic localisation and predominant neuronal expression, with widespread expression throughout the brain. None of three polypeptides carrying patient missense mutations affected the subcellular distribution of KCTD7. Discussion These data confirm the causality of KCTD7 defects in PME, and imply that KCTD7 mutation screening should be considered in PME patients with onset around 2 years of age followed by rapid mental and motor deterioration.

Vigabatrin caused rapidly progressive deterioration in two cases with early myoclonic encephalopathy associated with nonketotic hyperglycinemia

Vigabatrin, a structural analogue of γ-aminobutyric acid (GABA), is used for the treatment of generalized and partial seizures in infants. The drug inhibits the GABA transaminase and elevates the GABA concentration in the brain. Here we present the vigabatrin experience in two patients with early myoclonic encephalopathy owing to nonketotic hyperglycinemia (glycine encephalopathy). Both patients had early infantile seizures characterized by fragmentary myoclonic jerks associated with burst-suppression pattern on electroencephalography. Nonketotic hyperglycinemia was diagnosed with elevated cerebrospinal fluid and plasma glycine levels. The seizures were initially thought to be infantile spasms, and vigabatrin (50 mg /kg/day) was started for the treatment of seizures. Rapidly progressive deterioration was noticed after a few days. Acute encephalopathy associated with sleepiness and respiratory failure developed. Vigabatrin produced acute encephalopathy, which regressed in a few days after vigabatrin was stopped in the first patient. However, in the second case, despite the discontinuation of vigabatrin, there was no recovery of general conditions. Our observations in two cases indicate the risk of using vigabatrin in patients with nonketotic hyperglycinemia. The elevated GABA concentration in the brain can enhance the encephalopathy, together with the elevated levels of glycine. (J Child Neurol 2006;21:82—84).