doublecortin is the major gene causing X-linked subcortical laminar heterotopia (SCLH)

Subcortical laminar heterotopia (SCLH), or 'double cortex', is a cortical dysgenesis disorder associated with a defect in neuronal migration. Clinical manifestations are epilepsy and mental retardation. This disorder, which mainly affects females, can be inherited in a single pedigree with lissencephaly, a more severe disease which affects the male individuals. This clinical entity has been described as X-SCLH/LIS syndrome. Recently we have demonstrated that the doublecortin gene, which is localized on the X chromosome, is implicated in this disorder. We have now performed a systematic mutation analysis of doublecortin in 11 unrelated females with SCLH (one familial and 10 sporadic cases) and have identified mutations in 10/11 cases. The sequence differences include nonsense, splice site and missense mutations and these were found throughout the gene. These results provide strong evidence that loss of function of doublecortin is the major cause of SCLH. The absence of phenotype-genotype correlations suggests that X-inactivation patterns of neuronal precursor cells are likely to contribute to the variable clinical severity of this disorder in females.

A novel CNS gene required for neuronal migration and involved in X-linked subcortical laminar heterotopia and lissencephaly syndrome

X-SCLH/LIS syndrome is a neuronal migration disorder with disruption of the six-layered neocortex. It consists of subcortical laminar heterotopia (SCLH, band heterotopia, or double cortex) in females and lissencephaly (LIS) in males, leading to epilepsy and cognitive impairment. We report the characterization of a novel CNS gene encoding a 40 kDa predicted protein that we named Doublecortin and the identification of mutations in four unrelated X-SCLH/LIS cases. The predicted protein shares significant homology with the N-terminal segment of a protein containing a protein kinase domain at its C-terminal part. This novel gene is highly expressed during brain development, mainly in fetal neurons including precursors. The complete disorganization observed in lissencephaly and heterotopia thus seems to reflect a failure of early events associated with neuron dispersion.

Evidence of late-onset infantile spasms

PURPOSE

To underline the unusual but possible occurrence of epileptic spasms (ES) in children >1 year of age.

METHODS

Cases in whom onset of spasms occurred after 1 year of age were identified through a retrospective review of the records of all patients referred for ES to the Saint-Vincent de Paul Hôpital (Paris) and American Memorial Hospital (Reims) between 1974 and 1994.

RESULTS

Eighteen cases were identified among the 734 children referred for ES, 18 cases were identified where spasm onset time ranged from 12 to 38 months of age. In 1/3 of the cases, the diagnosis was suspected from the onset of clinical manifestations; in the remaining 2/3, diagnosis was delayed by a mean 6 months (range, 2-25 months). Neurobehavioral regression affected two-thirds of the patients. Modified hypsarrhythmia was present in 11 patients; all but one exhibited major and diffuse spike- and slow-wave activity. EEG abnormalities were detected in the frontal areas in 11 patients. Spasms were cryptogenic in 9 patients. Steroids were administered to 13 patients; these controlled the spasms in 6 patients. Outcome was favorable for both seizures; cognition favorable in only 2 of the 18 patients.

CONCLUSIONS

Beginning after the first year of life, ES, or late-onset infantile spasms, are distinct from early Lennox-Gastaut syndrome, although etiology, prognosis and treatment are similar to that for the classical infantile spasms.

Lamotrigine for generalized seizures associated with the Lennox-Gastaut syndrome. Lamictal Lennox-Gastaut Study Group

BACKGROUND

The Lennox-Gastaut syndrome, a severe form of epilepsy that usually begins in early childhood, is difficult to treat. Dose-related drug toxicity is common.

METHODS

We conducted a double-blind, placebo-controlled trial of the antiepileptic drug lamotrigine in patients with the Lennox-Gastaut syndrome. Eligible patients had more than one type of predominantly generalized seizure, including tonic-clonic, atonic, tonic, and major myoclonic, and had seizures on average at least every other day. After a 4-week base-line period in which all participants received placebo, we randomly assigned 169 patients (age range, 3 to 25 years) to 16 weeks of lamotrigine (n= 79) or placebo (n=90) in addition to their other antiepileptic drugs.

RESULTS

The median frequency of all major seizures changed from base-line levels of 16.4 and 13.5 per week in the lamotrigine and placebo groups, respectively, to 9.9 and 14.2 per week after 16 weeks of treatment (P=0.002). Thirty-three percent of the patients in the lamotrigine group and 16 percent of those in the placebo group had a reduction of at least 50 percent in the frequency of seizures (P= 0.01). There were no significant differences between groups in the incidence of adverse events, except for colds or viral illnesses, which was more common in the lamotrigine group (P=0.05).

CONCLUSIONS

Lamotrigine was an effective and well-tolerated treatment for seizures associated with the Lennox-Gastaut syndrome.

Early single photon emission computed tomography in Sturge-Weber syndrome

OBJECTIVES

Functional cerebral imaging PET and SPECT have shown hypometabolism and hypoperfusion in the area of vascular malformation in children with epilepsy due to Sturge-Weber syndrome. However, data are scarce in infants and do not exist in patients with Sturge-Weber disease without epilepsy. The pattern of perfusion during the first two years of life was studied including patients before the onset of seizures.

METHODS

Twenty two infants with later confirmed Sturge-Weber disease underwent SPECT examination using TOMOMATIC 564 (Medimatic) and xenon-133 at ages ranging from 8 days to 25 months. Twelve had never had seizures before SPECT and seven underwent a second SPECT a mean seven months later. Cerebral blood flow (CBF) was measured in the whole hemisphere and in the part of the cortex involved in the vascular malformation on both sides as well as a "pathological to normal" index for the hemisphere and vascular malformation. These values were compared with normal age paired values.

RESULTS

Compared with controls, CBF and the indices in the hemisphere and vascular malformation were significantly decreased in patients who already had had seizures before SPECT, whereas they were significantly increased in 75% of the patients who had never had any seizures. On second SPECT, the indices were decreased in all patients, including the four who still remained non-epileptic.

CONCLUSIONS

SPECT therefore detects CBF asymmetry in infants with Sturge-Weber disease, which tends to shift with age. The cortex involved in the vascular malformation is hyperperfused during the first year of life before first seizures. The classic hypoperfusion appears after one year of age, even in non-epileptic patients.

Dominant X linked subcortical laminar heterotopia and lissencephaly syndrome (XSCLH/LIS): evidence for the occurrence of mutation in males and mapping of a potential locus in Xq22

X linked subcortical laminar heterotopia and lissencephaly syndrome (XSCLH/ LIS) is an intriguing disorder of cortical development, which causes classical lissencephaly with severe mental retardation and epilepsy in hemizygous males, and subcortical laminar heterotopia (SCLH) associated with milder mental retardation and epilepsy in heterozygous females. Here we report an exclusion mapping study carried out in three unrelated previously described families in which males are affected with lissencephaly and females with SCLH, using 38 microsatellite markers evenly distributed on the X chromosome. Most of the X chromosome was excluded and potential intervals of assignment in Xq22.3-q23 or in Xq27 are reported. Although the number of informative meioses did not allow a decision between these two loci, it is worth noting that the former interval is compatible with the mapping of a breakpoint involved in a de novo X;autosomal balanced translocation 46,XX,t(X;2)(q22;p25) previously described in a female with classical lissencephaly. In addition, haplotype inheritance in two families showed a grandpaternal origin of the mutation and suggested in one family the presence of mosaicism in germline cells of normal transmitting males.

X-linked malformations of neuronal migration

Malformations of neuronal migration such as lissencephaly (agyria-pachygyria spectrum) are well-known causes of mental retardation and epilepsy that are often genetic. For example, isolated lissencephaly sequence and Miller-Dieker syndrome are caused by deletions involving a lissencephaly gene in chromosome 17p13.3, while many other malformation syndromes have autosomal recessive inheritance. In this paper, we review evidence supporting the existence of two distinct X-linked malformations of neuronal migration. X-linked lissencephaly and subcortical band heterotopia (XLIS) presents with sporadic or familial mental retardation and epilepsy. The brain malformation varies from classical lissencephaly, which is observed in males, to subcortical band heterotopia, which is observed primarily in females. The XLIS gene is located in chromosome Xq22.3 based on the breakpoint of an X-autosomal translocation. Bilateral periventricular nodular heterotopia (BPNH) usually presents with sporadic or familial epilepsy with normal intelligence, primarily in females, although we have evaluated two boys with BPNH and severe mental retardation. The gene for BPNH has been mapped to chromosome Xq28 based on linkage studies in multiplex families and observation of a subtle structural abnormality in one of the boys with BPNH and severe mental retardation.

Regional cerebral glucose metabolism in children with deterioration of one or more cognitive functions and continuous spike-and-wave discharges during sleep

The Landau-Kleffner syndrome (LKS) and the syndrome of continuous spike-and-wave discharges during slow sleep (CSWS) were originally described, and are still considered, separately. The former combines an acquired aphasia with spike-and-wave discharges that are activated by slow wave sleep, behavioural disturbances, and sometimes epileptic seizures. The latter is characterized by continuous spike-and-wave discharges during slow wave sleep, usually combined with global intellectual deterioration and epileptic seizures. These two syndromes share many common features: (i) onset during childhood; (ii) deterioration of cognitive functions that were previously normally acquired; (iii) seizure type; (iv) EEG pattern; (v) pharmacological reactivity; (vi) regression of the neuropsychological symptoms, of the EEG abnormalities and of the seizures before the end of adolescence; (vii) absence of obvious structural lesion detected by CT or MRI scan. Therefore, we postulated that these patients might, in fact, be presenting several facets of a single process associating the deterioration of cognitive functions and continuous spike-and-wave discharges during slow wave sleep. The pathogenesis of this syndrome remains unknown. Seven patients, presenting CSWS associated with neuropsychological deterioration (isolated aphasia, three cases; language disturbances with more widespread cognitive deterioration, three cases; isolated apraxia, one case) were studied using PET with [18F]fluorodeoxyglucose (FDG). We hoped to find metabolic arguments in favour of a unifying hypothesis, and to reveal clues as to pathogenesis. We present the retrospective analysis of 21 studies performed between 1986 and 1993, 12 of which were done during sleep. For three of these patients, follow-up studies were obtained until recovery. The metabolic patterns were very variable from one patient to another and in the same patient over time. Among the six patients studied during the active phase of the affection, our results showed unilateral, focal or regional increase in glucose metabolism of the cortex in five patients. This hypermetabolism was observed during sleep with continuous spike-and-wave discharges, but also persisted during wakefulness. In the last patient, the metabolic pattern was different: decreased regional glucose metabolism was observed during wakefulness, whereas during sleep, the metabolic pattern in the temporal areas varied during the course of the affection. After recovery, the metabolic pattern in four children (including the seventh patient) was either normal or showed focal or regional, uni- or bilateral decrease in cortical glucose metabolism. Despite this apparent disparity, four basic metabolic characteristics formed a common pattern in all patients, in line with our unifying postulate: (i) the metabolism of the cortical mantle was higher than in the subcortical structures, especially in the thalamic nuclei. This metabolic pattern is characteristic of an immature brain. (ii) The metabolic abnormalities involved focal or regional areas of the cortex. This finding is in good agreement with recent neurophysiological data suggesting a focal origin of the spike-and-wave discharges. (iii) The metabolic disturbances predominantly involved associative cortices. The pattern of neuropsychological deterioration is in good agreement with the topography of the disturbances of cortical glucose metabolism. (iv) The thalamic nuclei remained symmetrical despite significant cortical asymmetries, suggesting either that cortico-thalamic neurons do not participate in the generation of spike-and-wave discharges or that they are inhibited by the pathologic mechanisms. We hypothesize that the acquired deterioration of cognitive function with CSWS is caused by an alteration of the maturation of one or several associative cortices, primarily involving local interneurons and cortico-cortical associative neurons.

[Subcortical laminal heterotopia and lissencephaly: cerebral malformations of X-linked inheritance]

Subcortical laminar heterotopia (band heterotopia) is a brain malformation now recognized by MRI. We report 3 families (2 previously described) in which several members had subcortical laminar heterotopia or a more severe malformation (agyria/pachygyria). In these families, subcortical laminar heterotopia were observed in women and were associated with epilepsy or slight mental retardation depending on the extend of heterotopia. Males had lissencephaly with refractory epilepsy and severe mental retardation. The pedigrees of these families demonstrate that these 2 malformations originate from a single genetic origin. A single X-linked dominant gene is postulated. Diagnosis of subcortical laminar heterotopia in a female or lissencephaly in a male (except in the case of Miller-Dieker syndrome) requires appropriate genetic counselling in the family: brain imaging should be performed in relatives.

Genotypic subtypes of HIV-1 in Cameroon

OBJECTIVE

The only two HIV-1 strains (ANT70 and MVP5180) reported to date from Cameroon are members of the outlier clade (group O). In this study, we assessed the prevalence of group O viruses and other HIV-1 subtypes in Cameroon.

DESIGN

A phylogenetic analysis of 18 HIV-1 strains isolated from seropositive individuals from Yaoundé and Douala, Cameroon.

METHODS

A 900 base-pair fragment of the env gene coding for V3, V4, V5, and the beginning of gp41 of 17 out of 18 HIV-1 isolates from Cameroon was amplified, cloned and sequenced using polymerase chain reaction. A phylogenetic tree was constructed.

RESULTS

The overall env nucleotide sequence divergence among the Cameroon isolates ranged from 6.1 to 27.5%. In a phylogenetic tree, six subtypes were identified when compared with 23 reference strains of different geographic origin. Of these 17 Cameroonian strains, 11 (61%) were of subtype A of which the interpatient distances at the sequence level varied from 6.1% to 18.3% (average, 11.9%). Three (17%) strains were of subtype F, and the other three strains (6% each) belonged to subtypes B, E and H, respectively. The remaining isolate was classified as belonging to group O, on the basis of the sequence of part of the pol gene. A very broad spectrum of different tetrameric amino-acid sequences was observed at the apex of the V3 loop. Eleven strains contained the tetrameric globally predominant GPGQ sequence at the tip of the V3 motif. Two strains had the GPGR sequence typical of the American and European HIV-1 strains. The remaining tetrameric sequences included GPGS, GSGQ, GRGQ, and GLGR.

CONCLUSION

These findings on a limited number of viruses suggest extensive env gene diversity of HIV-1 strains from Cameroon, and could have implications for vaccine development in Africa.

Genetic and antigenic variability of HIV type 1 in Brazil

Six Brazilian strains of human immunodeficiency virus type 1 (HIV-1) were isolated from infected individuals residing in different regions of Brazil between 1987 and 1989. Phylogenetic analysis based on an 860-base pair env fragment, including V3, V4, V5, and the beginning of gp41, classified the Brazilian strains significantly in genotype B, with interhost distances between 5.9 and 13.1% (mean value, 10%). Amino acid sequence analysis of the V3 loop revealed that three strains contained the North American/European GPGR motif as the tip of the loop whereas in the other three strains proline (P) was substituted by tryptophan (W), methionine (M), or phenylalanine (F). A consensus peptide, Bra-cons, was designed containing GWGR as the tip of the loop. Serological reactivity to the Bra-cons peptide and other V3 peptides (MN, SF2, HBX2, RF, MAL, ELI, Z6, and a Côte d'Ivoire peptide, CI-cons) was compared for 114 HIV-1-positive sera from Rio de Janeiro. Sixty-nine sera (60.5%) reacted with peptides belonging to genotype B, of which 10 sera also reacted with peptides belonging to genotype A (n = 7) and D (n = 3). Eighteen sera (15.8%) had binding antibodies to the Bra-cons peptide. A high number of sera (n = 43; 37.7%) had no antibodies to any of the V3 peptides tested. This result suggests that HIV-1 variants with aberrant V3 loops may circulate in Rio de Janeiro.

Subcortical laminar heterotopia and lissencephaly in two families: a single X linked dominant gene

Neuronal migration disorders can now be recognised by MRI. This paper reports two families in which the mothers had subcortical laminar heterotopia and four of their children had either similar heterotopia (two girls) or severe pachygyria or lissencephaly (two boys). Laminar heterotopia was more evident on MRI T2 weighted images. The patients had mild to severe epilepsy and mental retardation depending on the extent of cortical abnormalities. In these families, subcortical laminar heterotopia, pachygyria, and lissencephaly seem to share the same X linked or autosomal dominant gene. No chromosomal abnormalities, especially of chromosome 17, could be identified. For appropriate genetic counselling of the family of a child with lissencephaly or subcortical laminar heterotopia, MRI should be performed in parents or siblings with mental retardation or epilepsy.

C-fos expression after single and kindled audiogenic seizures in Wistar rats

In naive Wistar rats susceptible to sound, a single audiogenic seizure induced the expression of c-fos in the subcortical auditory nuclei whereas the forebrain was almost completely devoid of any labelling. After kindling of audiogenic seizures by 40 daily exposures to sound, the seizure induced a strong c-fos expression in the amygdala, the piriform cortex, the hippocampus and the neocortex. These results confirm: (1) that audiogenic seizures are brain-stem seizures related to dysfunction of auditory pathways, and (ii) that kindling of audiogenic seizures recruits forebrain and limbic structures into the seizure network.

Molecular phylogeny of part of the env gene of HIV-1 strains isolated in Côte d'Ivoire

OBJECTIVES

To examine the genetic variation of HIV-1 isolates in Abidjan, Côte d'Ivoire, and to determine the extent to which phylogenetic trees based on sequence information of part of the env gene containing the principal neutralizing domain are representative for documenting genetic variability.

DESIGN

Phylogenetic comparison of 13 HIV-1 strains isolated from patients in Abidjan with previously documented HIV-1 strains of different geographic origin.

METHODS

To sequence a 900 base-pair fragment of the env gene containing V3, V4, V5 and the beginning of gp41 of three to four clones per isolate. Phylogenetic tree analysis was performed with the software package TREECON.

RESULTS

Eleven HIV-1 isolates of Abidjan were classified as genotype A, while two were classed as genotypes B and D. Intra-genotype A distances at the nucleotide level were a maximum of 14.1%. Inter-genotype distances between genotype A and genotypes B, C, and D varied from 16.0 to 22.6%. Phylogenetic trees, based on sequence data of a 300 base-pair fragment containing the V3 loop, showed significant differences in tree topology and statistical confidence with phylogenetic trees based on sequence data of the 900 base-pair env fragment.

CONCLUSIONS

Genotype A Côte d'Ivoire HIV-1 strains, which comprise 11 out of 13 isolates, predominate in Abidjan, which may indicate a local burst of particular variants. Phylogenetic trees should be interpreted with caution when based on a more limited number of nucleotides, such as the V3 region.

Neurofibromatosis type one and West syndrome: a relatively benign association

Fifteen patients with neurofibromatosis type one (NF1) and West syndrome (WS) were studied. The evolution of WS was clearly different from that seen in the other neurocutaneous syndromes, especially tuberous sclerosis. Steroids were efficacious and spasms disappeared. There was no relapse after discontinuation of steroids and antiepileptic drugs were successfully stopped several years later. Mental outcome was also very good. The association of both conditions does not seem to be a coincidence. WS with NF1 seems remarkably benign and resembles idiopathic WS more than symptomatic WS.