Monozygotic female twins with autism and the fragile-X syndrome (AFRAX)

The interplay between DNA methylation, folate and neurocognitive development

DNA methylation provides an attractive possible means for propagating the effects of environmental inputs during fetal life and impacting subsequent adult mental health, which is leading to increasing collaboration between molecular biologists, nutritionists and psychiatrists. An area of interest is the potential role of folate, not just in neural tube closure in early pregnancy, but in later major neurodevelopmental events, with consequences for later sociocognitive maturation. Here, we set the scene for recent discoveries by reviewing the major events of neural development during fetal life, with an emphasis on tissues and structures where dynamic methylation changes are known to occur. Following this, we give an indication of some of the major classes of genes targeted by methylation and important for neurological and behavioral development. Finally, we highlight some cognitive disorders where methylation changes are implicated as playing an important role.

Season of birth in autism: a fiction revisited

Variations of season of birth among autistic individuals were studied. The replicability of previously reported increases in birth rates in the months of March and August were examined in groups of individuals with autism or mental retardation (the comparison group). The sample was obtained from the Yale Child Study Center Developmental Disabilities Clinic and from the DSM-IV Autism/PDD field trial. Data were analyzed by applying the Jonckheere test of ordinal trend and the chi-square test, with Yates correction factor. With respect to March and August births, and with calculations based on the beginning and middle of the month, no significant seasonal effect was observed. Samples were subcategorized into verbal and mute groups, and again results failed to support the seasonality hypothesis.

The neurobiology and genetics of infantile autism

Autism is a syndrome with multiple etiologies, as is made clear both by the evidence of neurobiological research and by the catalog of disorders that present with autistic behaviors. What remains unclear are the specific neuropathological mechanisms that produce autistic behaviors; for example, is there a common neuroanatomic pathology for all cases of autism, or can autistic behaviors emerge from different pathological sequences within the brain? Although it is premature to generalize, neuropathological studies appear to have identified common abnormalities in the cerebellum and limbic system of at least five autistic subjects. These subjects, with variable levels of mental retardation, demonstrated marked Purkinje cell loss in the cerebellar hemispheres, together with retained fetal neuronal circuitry in cerebellar nuclei and increased neuronal packing in specific regions of the limbic system, amygdala, and hippocampus. The architecture of the cerebral cortex was not affected. Although our knowledge of brain functioning is incomplete, alterations of the kind noted in the cerebellum and limbic system could reasonably produce autistic behaviors. For more detail, readers are directed to a review of cerebellar contributions to higher functions by Schmahmann (1991). Neuroimaging studies allow less resolution of brain structure than do neuroanatomic studies, and the reported findings from neuroimaging are somewhat contradictory. However, a number of investigators have reported structural abnormalities in ventricle size and cerebral hemispheric asymmetry using CT. MRI, which offers greater resolution, has uncovered some consistent findings, along with a variety of nonspecific abnormalities. Common abnormalities include reduced volume of cerebellar hemispheres and vermal lobules--findings not inconsistent with the above-mentioned neuropathological defects. It is also interesting to note that individuals with fragile X syndrome have similar cerebellar findings. PET and NMR studies of autism are at a preliminary stage, but these methodologies allow insight into the functioning of the brain, rather than simply brain anatomy. Recent PET studies indicating decreased association between paired regions of the brains of autistic subjects are of interest, particularly if they can be confirmed and refined by additional studies. Neurophysiological studies also offer insight into brain function, but are subject to numerous methodological criticisms. Nevertheless, recent reports of diminished P300 waves and absent NC components in autistic subjects seem to indicate fundamental defects in attention and secondary processing, which could help explain the self-stimulatory behaviors often seen in autism. The disturbances in brain development associated with autism can be produced in a number of ways, and at different times during development of the nervous system.(ABSTRACT TRUNCATED AT 400 WORDS)

The fragile-X syndrome. On the way to a behavioural phenotype

The fragile-X syndrome accounts for up to 10% of individuals with mental handicap, and 50% of cases of X-linked mental retardation. Knowledge of the genetic basis of mental functioning, psychopathology, and neuropsychology is being furthered by this recently recognised condition. The disorder has considerable significance for psychiatrists, particularly, but by no means exclusively, those working in the field of mental handicap and with children. This review outlines the slow clarification of this complex and important behavioural phenotype and the implications of these advances for identification, diagnosis, genetic counselling and a wide range of management interventions.

Prevalence of fra(X) and other specific diagnoses in autistic individuals in a Danish county

In a Danish county (the island of Funen) cytogenetic screening for fragile X [fra(X)] of 32 autistic individuals aged 0-23 years showed a prevalence of 2/20 among boys and 0/12 among girls. In both cases additional fra(X) positive relatives were found. In 3 patients other chromosome aberrations were demonstrated and in one female Rett syndrome was diagnosed, initially suspected from observations of her behavior on videotapes. The presence of an underlying cause of autism in 6/32, of the patient group encourages an active search for a specific diagnosis among autistic males and females. Future screening of autistic individuals should include 1) fra(X) search also in females, 2) search for other chromosomal disorders, and 3) observation of behavior, in order to diagnose, i.e., Rett syndrome.

The syndromes described by Kanner and Rett-Hagberg: overlap in an extended family

An extended family is reported in which Rett-Hagberg syndrome, autism with mild ataxia and autism with profound mental retardation occurred separately in three female second-cousins. The authors suggest alternative explanations for the possible association between autism and Rett-Hagberg syndrome: that they may be closely related genetic disorders, or that they may constitute relatively homogeneous phenotypes with several possible aetiologies.

A twin study of autism in Denmark, Finland, Iceland, Norway and Sweden

The Nordic countries were screened for the occurrence of cases of autism with a same-sexed twin under age 25 years. Twenty-one pairs (11 monozygotic and 10 dizygotic) of twins and one set of identical triplets were found and extensively examined. The concordance for autism by pair was 91% in the monoygotic and 0% in the dizygotic pairs. The corresponding concordances for cognitive disorder were 91% and 30%, respectively. In most of the pairs discordant for autism, the autistic twin had more perinatal stress. The results lend support for the notion that autism sometimes has a hereditary component and that perinatal stress is involved in some cases.

Chromosome findings in twins with early-onset autistic disorder

In a twin study of autistic disorder, chromosome analyses were carried out in nine pairs of monozygotic (MZ) twins, two pairs of dizygotic (DZ) twins, one set of MZ triplets, one single twin from a MZ pair, and seven single twins from DZ pairs. All but one of the MZ sets were concordant for autistic disorder; all DZ pairs were discordant. Fragile X(q)(27.3) was found in one pair of MZ twins and in MZ triplets, i.e., in 9% of the population with autistic disorder. A marker chromosome of unknown origin was detected in a male twin with autistic disorder from a discordant DZ pair.