A helium-burning white dwarf binary as a supersoft X-ray source

Type Ia supernovae are cosmic distance indicators1,2, and the main source of iron in the Universe3,4, but their formation paths are still debated. Several dozen supersoft X-ray sources, in which a white dwarf accretes hydrogen-rich matter from a non-degenerate donor star, have been observed5 and suggested as Type Ia supernovae progenitors6-9. However, observational evidence for hydrogen, which is expected to be stripped off the donor star during the supernova explosion10, is lacking. Helium-accreting white dwarfs, which would circumvent this problem, have been predicted for more than 30 years (refs. 7,11,12), including their appearance as supersoft X-ray sources, but have so far escaped detection. Here we report a supersoft X-ray source with an accretion disk whose optical spectrum is completely dominated by helium, suggesting that the donor star is hydrogen-free. We interpret the luminous and supersoft X-rays as resulting from helium burning near the surface of the accreting white dwarf. The properties of our system provide evidence for extended pathways towards Chandrasekhar-mass explosions based on helium accretion, in particular for stable burning in white dwarfs at lower accretion rates than expected so far. This may allow us to recover the population of the sub-energetic so-called Type Iax supernovae, up to 30% of all Type Ia supernovae13, within this scenario.

Neurology training for the child neurologist

The training of the child neurologist in the fundamentals of neurology is discussed. Although the fundamentals of neurology are clearly necessary for the practice of child neurology, the breadth of the background necessary for the practice of child neurology depend on the interest, enthusiasm, and goals of the resident in question. Some of the issues involved in the design and implementation of the training curriculum will be considered.

Benign afebrile seizures in acute gastroenteritis: is rotavirus the culprit?

Three patients, a 2-year-old girl, a 14-month-old girl, and a 15-month-old boy, were admitted with multiple episodes of benign afebrile seizures. Electroencephalograms recorded 1 or 2 days after the last seizure revealed epileptiform discharges. All 3 patients developed a fulminant Rotazyme-positive diarrhea toward the end of their respective hospital stay. The prospects of immunological detection in diagnosis and treatment are discussed.

Childhood-onset spastic paraplegia with NIPAL gene mutation

Hereditary spastic paraplegia is a heterogeneous group of inherited neurodegenerative disorders in which the predominant clinical feature is gait disturbance owing to spasticity and weakness of the lower limbs. Autosomal dominant hereditary spastic paraplegia is the predominant form of the disorder. To date, 10 autosomal dominant hereditary spastic paraplegia gene loci and genes for 6 of them have been identified. Spastic paraplegia 6, with a typical teenage onset and considered to be one of the more severe forms of the disease, is due to mutations in the gene NIPA1. We report a childhood-onset, aggressive, spastic paraparesis in a North American family with a c.316G>A mutation of the NIPA1 gene, confirming c.316 as a mutational hot spot.

Myoclonus epilepsy with ragged red fibers and multiple mtDNA deletions

In a patient with clinical features of myoclonus epilepsy with ragged red fibers (MERRF), molecular genetic analysis of mitochondrial DNA did not show either of the two point mutations typically associated with MERRF but did show multiple deletions by Southern blot. This case further illustrates the heterogeneity observed with mtDNA mutations.

Neuropharmacology of progressive myoclonus epilepsy: response to 5-hydroxy-L-tryptophan

Low concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) in cerebrospinal fluid (CSF) of patients with progressive myoclonus epilepsy (PME) suggest hypofunctional serotonergic neurotransmission. To study this hypothesis, we enrolled 6 patients with PME [Unverricht-Lündborg disease (U-L), mitochondrial encephalomyopathy, or Lafora disease] in a controlled, double-blinded, dose-ranging, cross-over add-on pilot clinical trial of 5-hydroxy-L-tryptophan (L-5-HTP) plus carbidopa after 2 other patients had received open-label L-5-HTP for compassionate use. Prestudy CSF 5-HIAA concentrations were low (< 20 ng/ml) in 6 patients regardless of the etiology of PME. One patient with U-L disease showed clinical improvement and a fivefold increase in CSF 5-HIAA, and 1 with Lafora disease showed a twofold increase in CSF 5-HIAA without improvement. A patient with Lafora disease reported enough improvement in myoclonus-evoked convulsions to continue chronic use of the drug. One patient with mitochondrial encephalomyopathy developed status epilepticus during treatment with L-5-HTP. As a group, patients had no statistically significant changes in myoclonus evaluation scale scores, subjective and objective measures of ataxia, seizure frequency, antiepileptic drug (AED) levels, or routine blood tests. These data suggest a serotonergic abnormality regardless of the underlying etiology of PME, but one that seldom responds to acute treatment with L-5-HTP.

Electrodiagnosis of infantile botulism

Analysis of the literature on the electrophysiologic features of infantile botulism was undertaken. Small compound muscle action potential amplitude is a very sensitive feature but lacks specificity. The decremental response to 2- to 3-Hz repetitive nerve stimulation is inconsistent and not a reliable sign. Tetanic and posttetanic facilitation are highly sensitive and highly specific. Absence of posttetanic exhaustion is also highly specific for infant botulism and shared only by hypermagnesemia. We conclude that the findings of low compound muscle action potential amplitude in combination with tetanic facilitation or posttetanic facilitation and absence of posttetanic exhaustion constitute the triad on which the electrodiagnosis of infantile botulism can be supported.

Treatment of spastic gait in cerebral palsy

The most common presentation of cerebral palsy is spastic diplegia, which in severe cases can impede nursing care and in less severe cases can impair a child's ability to move around with facility. A procedure has been developed to decrease spasticity in which there is selective section of portions of the dorsal roots L2-S2. In a series of such operations in 19 children with spastic diplegia, we were able to decrease their spasticity significantly with resultant improvement in motor function and self care. There were no significant complications and patient and family satisfaction was high. Our experiences further confirm existing evidence that this procedure is very helpful and highly recommended for selected children with spasticity due to cerebral palsy.

Hypoplasia of the corpus callosum: a study of 445 consecutive MRI scans

The size of the corpus callosum was assessed visually and by computer-assisted image analysis in a series of 445 consecutive magnetic resonance imaging (MRI) scans in children under 17 years of age. Fifty individuals were subjectively identified with small corpora callosa on visual inspection of the MRI scans. Seven patients had true hypoplasia of the corpus callosum after comparing the computer-measured relative size of the structure to previously established normal values. Five additional patients had complete agenesis, and two had partial agenesis of the corpus callosum. The cognitive functional levels of the seven patients with callosal hypoplasia and a control group of 63 randomly selected individuals from the remainder of the group were ascertained by record review. Seventy-one percent of the patients with hypoplasia of the corpus callosum and 29% of the control group had impaired function. The P value determined by Fisher's exact test was P = .061, suggesting that further study with greater numbers may be warranted. The prevalence of mental retardation in this condition, and the fact that hypoplasia is as common as complete and partial agenesis of the corpus callosum combined, suggest that hypoplasia of the corpus callosum is a marker of cerebral dysgenesis that should be looked for in the appropriate clinical setting.

Newly recognized congenital myasthenic syndrome associated with high conductance and fast closure of the acetylcholine receptor channel

We describe here a new congenital myasthenic syndrome associated with a kinetic abnormality of the acetylcholine receptor (AChR) channel. The propositus had poor suck and cry after birth. Subsequently, she had intermittent ocular symptoms and fatigued abnormally on exertion. At age 9 years, significant weakness was detected only in the frontalis, levator palpebrae, and neck flexor muscles. Electromyography showed no decrement in limb muscles but single-fiber examination of the facial muscles was consistent with a neuromuscular transmission defect. The ocular symptoms responded partially to pyridostigmine, but the abnormal fatigability did not. Tests for anti-AChR antibodies were negative. A younger sister had elements of the same disease. An intercostal muscle specimen was obtained from the propositus at age 9 years for endplate studies. The quantal content of the endplate potential was normal. Miniature endplate currents were abnormally large and their decay time constant was abnormally short. AChR channel properties were studied by analysis of acetylcholine-induced current noise. The mean single-channel conductance was increased 1.7-fold and the mean channel open time was 30% shorter than normal. The number of AChR per endplate was normal. Electron microscopy of most endplates showed no abnormality, but a few were degenerating or simplified. The channel abnormality may stem from a point mutation in an AChR subunit affecting a single amino acid residue lining the pore of the AChR channel. The mechanism by which the physiological abnormality produces clinical symptoms is not known, but possible explanations are considered.

Spontaneous intracerebral hemorrhage: a very late delayed effect of radiation therapy

Cerebral necrosis is a well-known delayed sequela of radiation to the central nervous system. Delayed intracerebral hemorrhage occurring several years after radiation is rare; however, with increased survival, this complication will become more common. We report a child who developed a brain-stem hemorrhage 4.5 years following radiation therapy for brainstem tumor. The possible pathogenesis for the spontaneous hemorrhage is discussed. The onset of the neurologic symptoms in this setting occurs later than the usual symptoms of radiation necrosis. It is important to recognize this entity as a late delayed complication of radiation therapy and not to mistake it for tumor recurrence.

Dipole reversal: an ictal feature of benign partial epilepsy with centrotemporal spikes

Benign epilepsy with centrotemporal spikes (BECTS) is characterized by brief stereotypical partial seizures with motor and/or sensory symptoms with frequent secondarily generalized seizures. The interictal EEG shows slow, disphasic, high-voltage spikes in the centrotemporal areas. The few published examples of ictal tracings depict focal rhythmic sharp waves and spikes without significant postictal slowing. We report an ictal event in BECTS that is unusual in the evolution and polarity of the ictal discharges. In this subclinical seizure, ictal multiple spike and wave discharges appear as a dipole: they are electropositive in T3-C3 and negative in F3. These surface positive epileptic discharges are unique and require explanation. We postulate that the seizure discharge arises in the depths of the sylvian fissure involving folded cortical areas. This occurs in such a way that the negative component of the discharges is concealed from the scalp electrodes. Thus, a relative positivity is recorded on the surface. This represents a dipole reversal relative to the interictal discharges (characteristic of BECTS). This geometrical explanation allows us to avoid postulating an unusual mechanism of generation of this seizure.

Colpocephaly: pitfalls in the diagnosis of a pathologic entity utilizing neuroimaging techniques

Colpocephaly has been described as the persistence of the fetal configuration of the lateral ventricles. The pathologic picture is characterized by multiple features of disturbed or arrested development of the brain, which results in diminished thickness of the cerebral white matter in the posterior portion of the centrum semiovale, giving rise to large occipital horns of the lateral ventricles. This ventricular configuration allows the clinician to suspect the presence of this developmental disturbance utilizing computed tomographic images. In this paper, we present a case that demonstrates that not every patient with enlargement of the posterior horns of the lateral ventricles has the underlying developmental abnormalities that constitute colpocephaly as described by Yakovlev and Wadsworth. Furthermore, we point out the difficulties that can arise in the attempt to make a diagnosis of a pathologically defined condition on the basis of neuroimaging results alone.

X-linked olivopontocerebellar atrophy

We present a kindred with a relatively pure cerebellar degeneration that demonstrates X-linked recessive inheritance. The unique clinical picture of affected patients in our kindred is characterized by an infantile onset of ataxia; very slow rate of progression; normal strength, reflexes, and sensation; and cerebellar degeneration with involvement of the olive and pons demonstrated by neuroimaging techniques. The distinction between this and other reported olivopontocerebellar degenerations is made on the basis of the clinical features and mode of inheritance. It is not clear if the distinct clinical pattern in this kindred represents variable expression of a previously reported condition, allelic variance of previously reported kindreds, or a separate clinical entity. Molecular analysis, currently underway, may help settle the issue.

Congenital myopathies

The evaluation of the "floppy infant" is a common problem for neurologists who deal with infants. One major category of diseases to consider in the diagnosis of hypotonia in the infant is the congenital myopathies. The congenital myopathies are a group of nonprogressive primary diseases of muscle that present in infancy with hypotonia and weakness and that are subdivided on the basis of the morphologic characteristics seen on histochemical study of the muscle. These diseases share many clinical features despite demonstrating a wide range of variation. Through the study of the various congenital myopathies, considerable knowledge of the structural components of the muscle fiber and their function has been gained. Despite this, our understanding of these conditions is incomplete at this time.

Dominantly inherited craniodiaphyseal dysplasia: a new craniotubular dysplasia

We describe a mother and her male infant affected with a craniotubular dysplasia characterized by severe craniofacial hyperostosis and sclerosis with obliteration of paranasal sinuses and foramina of the skull base. Subsequent severe bilateral hearing loss and facial diplegia with relative sparing of the optic nerves were noted. The long bones show extreme asymmetric hyperostosis and sclerosis of the diaphyses and evidence of a modelling defect in the metaphyses. The spine, ribs, clavicles, and pelvis all show some degree of sclerosis and defective modelling, but are less severely involved. According to the definition by Gorlin, this disorder would best be classified as craniodiaphyseal dysplasia. Distinguishing features in these two patients as contrasted to previously described cases include a greater degree of hyperostosis and sclerosis than that described for other patients with craniodiaphyseal dysplasia, apparent dominant transmission, and significant metaphyseal involvement.

Progressive ascending paralysis following administration of intrathecal and intravenous cytosine arabinoside. A Pediatric Oncology Group study

Two childhood acute myelogenous leukemia (AML) patients receiving intrathecal (IT) and intravenous (IV) cytosine arabinoside (Ara-C) developed progressive ascending paralysis, resulting in death in one patient. Necropsy findings on this patient included spinal cord demyelination characteristic of Ara-C neurotoxicity. An unusual aspect of these two cases was the delay between cessation of IT therapy and the onset of neurologic symptoms. These patients received relatively low total doses of IT Ara-C and standard doses of IV Ara-C. Previous studies have shown that Ara-C equilibrates readily between serum and cerebrospinal fluid; this implies that total IV and IT doses of Ara-C may be additive in relation to development of neurotoxicity. For these reasons, use of IV and IT Ara-C in childhood AML must be approached with greater caution, especially if neurologic abnormalities develop during or after therapy.

Benign subdural collections of infancy

Four asymptomatic infants with macrocrania, abnormal transillumination, and characteristic computed tomography scans are described. All had bilateral subdural collections, normal brain size, modest ventricular enlargement, and prominent cerebral sulci and interhemispheric fissures. Although these latter findings are often interpreted as atrophy, these infants had normal development and rapidly growing heads. No treatment beyond diagnostic subdural punctures was performed. After up to 13 months of follow-up, the size of the subdural collections was either stable or decreasing in all four infants.

EEG in benign intracranial hypertension

A retrospective study of standard EEG's obtained from 26 patients with benign intracranial hypertension was done with particular emphasis on the effect of age on the EEG findings. Abnormal EEG's were found in 10 patients, all were less than 20 years of age. Although no consistent pattern of EEG abnormality could be identified, there appears to be a difference between the immature and adult brain in the EEG response to intracranial hypertension.

Electrically elicited blink reflex in normal neonates

The electrically elicited blink reflex was tested in 30 full-term neonates. Of the two distinctly separate responses, early component R1 and late component R2, R1 was recorded in all but three infants. Its latency, 12.1+/-1.0 msec (mean+/-SD), was significantly greater than that in adults (10.6+/-0.8 msec) despite a considerably shorter length of the reflex arc in infants. Unlike the response in adults, R2 was elicited in only 20 of 30 infants, mostly on the side ipsilateral to the stimulus. The reduction of reflex excitability of R2 in neonates must occur primarily at the level of interneurons since oligosynaptic R1 was elicited with ease whereas polysynaptic R2 was not.