Sleep in Autism Spectrum Disorder and Attention Deficit Hyperactivity Disorder

SLEEP IN AUTISM SPECTRUM DISORDER AND ATTENTION DEFICIT HYPERACTIVITY DISORDER: Kanwaljit Singh, Andrew W. Zimmerman Seminars in Pediatric Neurology Volume 22, Issue 2, June 2015, Pages 113-125 Sleep problems are common in autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD). Sleep problems in these disorders may not only worsen daytime behaviors and core symptoms of ASD and ADHD but also contribute to parental stress levels. Therefore, the presence of sleep problems in ASD and ADHD requires prompt attention and management. This article is presented in 2 sections, one each for ASD and ADHD. First, a detailed literature review about the burden and prevalence of different types of sleep disorders is presented, followed by the pathophysiology and etiology of the sleep problems and evaluation and management of sleep disorders in ASD and ADHD.

Randomized controlled trial of sulforaphane and metabolite discovery in children with Autism Spectrum Disorder

Background

Sulforaphane (SF), an isothiocyanate in broccoli, has potential benefits relevant to autism spectrum disorder (ASD) through its effects on several metabolic and immunologic pathways. Previous clinical trials of oral SF demonstrated positive clinical effects on behavior in young men and changes in urinary metabolomics in children with ASD.

Methods

We conducted a 15-week randomized parallel double-blind placebo-controlled clinical trial with 15-week open-label treatment and 6-week no-treatment extensions in 57 children, ages 3–12 years, with ASD over 36 weeks. Twenty-eight were assigned SF and 29 received placebo (PL). Clinical effects, safety and tolerability of SF were measured as were biomarkers to elucidate mechanisms of action of SF in ASD.

Results

Data from 22 children taking SF and 23 on PL were analyzed. Treatment effects on the primary outcome measure, the Ohio Autism Clinical Impressions Scale (OACIS), in the general level of autism were not significant between SF and PL groups at 7 and 15 weeks. The effect sizes on the OACIS were non-statistically significant but positive, suggesting a possible trend toward greater improvement in those on treatment with SF (Cohen’s d 0.21; 95% CI − 0.46, 0.88 and 0.10; 95% CI − 0.52, 0.72, respectively). Both groups improved in all subscales when on SF during the open-label phase. Caregiver ratings on secondary outcome measures improved significantly on the Aberrant Behavior Checklist (ABC) at 15 weeks (Cohen’s d − 0.96; 95% CI − 1.73, − 0.15), but not on the Social Responsiveness Scale-2 (SRS-2). Ratings on the ABC and SRS-2 improved with a non-randomized analysis of the length of exposure to SF, compared to the pre-treatment baseline (p < 0.001). There were significant changes with SF compared to PL in biomarkers of glutathione redox status, mitochondrial respiration, inflammatory markers and heat shock proteins. Clinical laboratory studies confirmed product safety. SF was very well tolerated and side effects of treatment, none serious, included rare insomnia, irritability and intolerance of the taste and smell.

Limitations

The sample size was limited to 45 children with ASD and we did not impute missing data. We were unable to document significant changes in clinical assessments during clinical visits in those taking SF compared to PL. The clinical results were confounded by placebo effects during the open-label phase.

Conclusions

SF led to small yet non-statistically significant changes in the total and all subscale scores of the primary outcome measure, while for secondary outcome measures, caregivers’ assessments of children taking SF showed statistically significant improvements compared to those taking PL on the ABC but not the SRS-2. Clinical effects of SF were less notable in children compared to our previous trial of a SF-rich preparation in young men with ASD. Several of the effects of SF on biomarkers correlated to clinical improvements. SF was very well tolerated and safe and effective based on our secondary clinical measures.

Trial registration: This study was prospectively registered at clinicaltrials.gov (NCT02561481) on September 28, 2015. Funding was provided by the U.S. Department of Defense.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13229-021-00447-5.

Developmental regression and mitochondrial function in children with autism

BACKGROUND

Developmental regression (DR) occurs in about one-third of children with Autism Spectrum Disorder (ASD) yet it is poorly understood. Current evidence suggests that mitochondrial function in not normal in many children with ASD. However, the relationship between mitochondrial function and DR has not been well-studied in ASD.

METHODS

This cross-sectional study of 32 children, 2 to 8 years old with ASD, with (n = 11) and without (n = 12) DR, and non-ASD controls (n = 9) compared mitochondrial respiration and mtDNA damage and copy number between groups and their relation to standardized measures of ASD severity.

RESULTS

Individuals with ASD demonstrated lower ND1, ND4, and CYTB copy number (Ps < 0.01) as compared to controls. Children with ASD and DR had higher maximal oxygen consumption rate (Ps < 0.02), maximal respiratory capacity (P < 0.05), and reserve capacity (P = 0.01) than those with ASD without DR. Coupling Efficiency and Maximal Respiratory Capacity were associated with disruptive behaviors but these relationships were different for those with and without DR. Higher ND1 copy number was associated with better behavior.

CONCLUSIONS

This study suggests that individuals with ASD and DR may represent a unique metabolic endophenotype with distinct abnormalities in respiratory function that may put their mitochondria in a state of vulnerability. This may allow physiological stress to trigger mitochondrial decompensation as is seen clinically as DR. Since mitochondrial function was found to be related to ASD symptoms, the mitochondria could be a potential target for novel therapeutics. Additionally, identifying those with vulnerable mitochondrial before DR could result in prevention of ASD.

Investigating Potential Biomarkers in Autism Spectrum Disorder

Background

Early identification and treatment of individuals with autism spectrum disorder (ASD) improves outcomes, but specific evidence needed to individualize treatment recommendations is lacking. Biomarkers that could be routinely measured within the clinical setting could potentially transform clinical care for patients with ASD. This demonstration project employed collection of biomarker data during regular autism specialty clinical visits and explored the relationship of biomarkers with clinical ASD symptoms.

Methods

Eighty-three children with ASD, aged 5–10 years, completed a multi-site feasibility study integrating the collection of biochemical (blood serotonin, urine melatonin sulfate excretion) and clinical (head circumference, dysmorphology exam, digit ratio, cognitive and behavioral function) biomarkers during routine ASD clinic visits. Parents completed a demographic survey and the Aberrant Behavior Checklist-Community. Cognitive function was determined by record review. Data analysis utilized Wilcoxon two-sample tests and Spearman correlations.

Results

Participants were 82% male, 63% White, 19% Hispanic, with a broad range of functioning. Group means indicated hyperserotonemia. In a single regression analysis adjusting for race and median household income, higher income was associated with higher levels of blood serotonin and urine melatonin sulfate excretion levels (p = 0.004 and p = 0.04, respectively). Melatonin correlated negatively with age (p = 0.048) and reported neurologic problems (p = 0.02). Dysmorphic status correlated with higher reported stereotyped behavior (p = 0.02) and inappropriate speech (p = 0.04).

Conclusion

This demonstration project employed collection of multiple biomarkers, allowed for examination of associations between biochemical and clinical measures, and identified several findings that suggest direction for future studies. This clinical research model has promise for integrative biomarker research in individuals with complex, heterogeneous neurodevelopmental disorders such as ASD.

Sulforaphane from Broccoli Reduces Symptoms of Autism: A Follow-up Case Series from a Randomized Double-blind Study

Introduction

Autism spectrum disorder (ASD) affects 1 in 68 children, is characterized by impaired social interaction and communication as well as restricted or repetitive behaviors, and varies widely with respect to its causes and presentations. There are no validated pharmacologic treatments for the core symptoms of ASD. The social, medical, and economic burdens of ASD on families and caregivers are profound. We recently showed in a small clinical trial that sulforaphane (SF) from broccoli sprouts could significantly reduce the behavioral symptoms of ASD.

Methods

After we completed the intervention phase of the original trial (2011–2013), many caregivers used over-the-counter dietary SF supplements in order to attempt to maintain improvements similar to those noted during the intervention. We periodically followed the progress of study participants through the summer of 2016.

Results

Families of 16 of the 26 subjects who received SF as part of the original study responded to requests for further information. Of these subjects, 6 did not continue taking SF supplements after the study. Nine of the 16 subjects are still taking an SF supplement and a 10th planned to. We present the edited testimonials of their caregivers in this case series.

Conclusions

Many parents and caregivers articulated the positive effects of SF, both during the intervention phase and in the ensuing 3 years reported herein. These observations may contribute to understanding ASD and to treatments that may alleviate some of its symptoms. Diet- and supplement-based therapies deserve careful consideration for their potential to provide vital clinical as well as biochemical information about ASD.

Sulforaphane Treatment of Young Men with Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) comprises a heterogeneous group of neurodevelopmental disorders that begin in early childhood. They are characterized by differences in behavior and delays in communication and affect at least 1% of children. Observational studies have now confirmed that behaviors of a substantial percentage of children with autism tend to improve with the onset of febrile illness, which might be the downstream effects of altered metabolic pathways involving increased expression of heat shock proteins (HSP) and cellular stress responses. Sulforaphane, a phytochemical derived from a number of cruciferous vegetables, most notably broccoli sprouts, has metabolic effects that in some ways resemble that of fever. This review paper discusses this "fever effect" and the intracellular effects of sulforaphane as well as the results of our recent clinical trial of sulforaphane in young adults with autism. The accompanying review by Liu et al. describes the cellular actions of sulforaphane and potential biomarkers in the study of ASD.

Sleep in Autism Spectrum Disorder and Attention Deficit Hyperactivity Disorder

Sleep problems are common in autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD). Sleep problems in these disorders may not only worsen daytime behaviors and core symptoms of ASD and ADHD but also contribute to parental stress levels. Therefore, the presence of sleep problems in ASD and ADHD requires prompt attention and management. This article is presented in 2 sections, one each for ASD and ADHD. First, a detailed literature review about the burden and prevalence of different types of sleep disorders is presented, followed by the pathophysiology and etiology of the sleep problems and evaluation and management of sleep disorders in ASD and ADHD.

Prenatal SSRI use and offspring with autism spectrum disorder or developmental delay

OBJECTIVE

To examine associations between prenatal use of selective serotonin reuptake inhibitors (SSRIs) and the odds of autism spectrum disorders (ASDs) and other developmental delays (DDs).

METHODS

A total of 966 mother-child pairs were evaluated (492 ASD, 154 DD, 320 typical development [TD]) from the Childhood Autism Risks from Genetics and the Environment (CHARGE) Study, a population-based case-control study. Standardized measures confirmed developmental status. Interviews with biological mothers ascertained prenatal SSRI use, maternal mental health history, and sociodemographic information.

RESULTS

Overall, prevalence of prenatal SSRI exposure was lowest in TD children (3.4%) but did not differ significantly from ASD (5.9%) or DD (5.2%) children. Among boys, prenatal SSRI exposure was nearly 3 times as likely in children with ASD relative to TD (adjusted odds ratio [OR]: 2.91; 95% confidence interval [CI]: 1.07-7.93); the strongest association occurred with first-trimester exposure (OR: 3.22; 95% CI: 1.17-8.84). Exposure was also elevated among boys with DD (OR: 3.39; 95% CI: 0.98-11.75) and was strongest in the third trimester (OR: 4.98; 95% CI: 1.20-20.62). Findings were similar among mothers with an anxiety or mood disorder history.

CONCLUSIONS

In boys, prenatal exposure to SSRIs may increase susceptibility to ASD or DD. Findings from published studies on SSRIs and ASD continues to be inconsistent. Potential recall bias and residual confounding by indication are concerns. Larger samples are needed to replicate DD results. Because maternal depression itself carries risks for the fetus, the benefits of prenatal SSRI use should be carefully weighed against potential harms.

Association between regression and self injury among children with autism

Self injurious behaviors (SIBs) are challenging clinical problems in individuals with autism spectrum disorders (ASDs). This study is one of the first and largest to utilize inpatient data to examine the associations between autism, developmental regression, and SIBs. Medical records of 125 neurobehavioral hospitalized patients with diagnoses of ASDs and SIBs between 4 and 17 years of age were reviewed. Data were collected from medical records on the type and frequency of SIBs and a history of language, social, or behavioral regression during development. The children with a history of any type of developmental regression (social, behavioral, or language) were more likely to have a diagnosis of autistic disorder than other ASD diagnoses. There were no significant differences in the occurrence of self injurious or other problem behaviors (such as aggression or disruption) between children with and without regression. Regression may influence the diagnostic considerations in ASDs but does not seem to influence the clinical phenotype with regard to behavioral issues. Additional data analyses explored the frequencies and subtypes of SIBs and other medical diagnoses in ASDs, with intellectual disability and disruptive behavior disorder found most commonly.

Altered postnatal cell proliferation in brains of mouse pups prenatally exposed to IgG from mothers of children with autistic disorder

Auto antibodies found in the mothers of children with autistic disorder (MCAD) when passively transferred to pregnant mice cause behavioral alterations in juvenile and adult offspring. The goal of this study was to identify whether intraperitoneal injection of MCAD-IgG during gestation affected postnatal cell proliferation and survival in P7 offspring. Pooled MCAD-IgG or IgG from mothers of unaffected children (MUC) or phosphate-buffered saline was injected daily into C57BL/J6 pregnant dams (gestational days E13–E18). MCAD-IgG exposure significantly increased cell proliferation in the subventricular and subgranular zones. In contrast, BrdU-labeled cells on P1 and surviving until P7 (P1-generated cells) showed reduced cell densities in layers 2–4 of frontal and parietal cortices of MCAD mice compared to those in MUC and PBS-injected mice. In conclusion, significant increases in cell proliferation at P7 and reduced densities of P1-generated cells distinguish in utero exposure to MCAD compared to MUC and PBS.

Maternal antibody reactivity to lymphocytes of offspring with autism

The study examined whether maternal serum antibodies from mothers of autistic children preferentially bind to lymphocytes of their autistic children compared with unaffected siblings. In a previous study, maternal serum antibodies from mothers mediated cytotoxicity with complement to lymphocytes of their autistic children. Here, maternal serum antibody binding was examined by flow cytometry. We compared levels of mothers' serum binding against peripheral blood monocytes of their autistic children vs unaffected siblings. Because the level of binding to peripheral blood monocytes could be low, binding was examined in specific lymphocyte subpopulations. In 19 samples, the mean level of maternal serum immunoglobulin G binding to CD4 and CD8 T cells, B cells, natural killer cells, and macrophages was not significantly different from the mean level of binding to unaffected siblings. The percentages of different subpopulations were not significantly different between autistic children and unaffected siblings, although a trend (P < 0.1) emerged, i.e., autistic children displayed a higher percentage of natural killer cells and a lower percentage of B cells. These findings cast doubt on a direct effect of maternal antibodies, but do not preclude potential intrauterine pathogenic immune mechanisms in autism.

Co-occurring conditions and change in diagnosis in autism spectrum disorders

OBJECTIVE

This study aimed to investigate descriptive characteristics and co-occurring neurodevelopmental and psychiatric conditions in young children, children, and adolescents with a current and consistent or past but not current (PBNC) diagnosis of autism spectrum disorder (ASD) and how such characteristics and conditions may engender a change in diagnosis of an ASD.

METHODS

Cross-sectional data of 1366 children with a parent-reported current or PBNC ASD diagnosis were obtained from the National Survey of Children's Health 2007 data set across 3 developmental stages: young children (aged 3-5 years), children (aged 6-11 years), and adolescents (aged 12-17 years). Multinomial logistic regression was used to examine demographic characteristics and co-occurring conditions that differentiate the groups with a current ASD from groups with a PBNC ASD.

RESULTS

Results indicated the co-occurring conditions that distinguish groups currently diagnosed with an ASD from groups with a PBNC ASD diagnosis. In young children, current moderate/severe learning disability, and current moderate/severe developmental delay; in children, past speech problem, current moderate/severe anxiety, and past hearing problem; and in adolescents, current moderate/severe speech problem, current mild seizure/epilepsy, and past hearing problem.

CONCLUSIONS

These findings suggest that the presence of co-occurring psychiatric and neurodevelopmental conditions are associated with a change in ASD diagnosis. Questions remain as to whether changes in diagnosis of an ASD are due to true etiologic differences or shifts in diagnostic determination.

In utero beta 2 adrenergic agonist exposure and adverse neurophysiologic and behavioral outcomes

Beta 2 adrenergic receptor overstimulation during critical periods of prenatal development can induce a permanent shift in the balance of sympathetic-to-parasympathetic tone. This is a biologically plausible mechanism whereby beta 2 adrenergic agonists can induce functional and behavioral teratogenesis, which explains their association with increases in autism spectrum disorders, psychiatric disorders, poor cognitive, motor function and school performance, and changes in blood pressure in the offspring. The use of beta 2 adrenergic agonists should be limited to proven indications when alternate drugs are ineffective or unavailable; the risks of untreated disease to the mother and fetus are greater than the risk of the beta 2 adrenergic agonist.

Childhood serum anti-fetal brain antibodies do not predict autism

Autoimmune hypotheses for autism include in utero transplacental exposure to maternal antibodies and acquired postnatal insults. Previous work demonstrated that some mothers of children with autistic disorder have specific antibodies against human fetal brain that differentiate them from mothers with typical children. In the present study, Western immunoblotting was used to determine whether children with autistic spectrum disorders (n = 29) have serum reactivity against human fetal brain that differs from that of controls (n = 14). There was no significant difference in reactivity, corrected for serum immunoglobulin G content and brain actin content and with special attention to reactive bands at 36, 39, 61, and 73 kDa, between autistic children and normal control subjects. Thus, in contrast to mothers, antibody reactivity against human fetal brain as measured in children ages 3-12 years does not appear to be a useful biomarker for autism.

Prenatal exposure to antibodies from mothers of children with autism produces neurobehavioral alterations: A pregnant dam mouse model

A pregnant mouse model was used to compare the effect of IgG, administered E13-E18, from mothers of children with autistic disorder (MCAD), to controls (simple- and IgG-) on behavioral testing in offspring. Mice, exposed in-utero to MCAD-IgG, as adolescents, were more active during the first ten minutes of central field novelty testing and, as adults, displayed anxiety-like behavior on a component of the elevated plus maze and had a greater magnitude of startle following acoustic stimulation. On a social interaction paradigm, adult mice had alterations of sociability. Pilot studies of immune markers in MCAD IgG-exposed embryonic brains suggest evidence of cytokine and glial activation. These studies demonstrate that the transplacental passage of IgG from MCAD is capable of inducing long-term behavioral consequences.

Variation in season of birth in singleton and multiple births concordant for autism spectrum disorders

Patterns of seasonal variation in births in some neuropsychiatric conditions have been found in previous research; however, no study to date has examined these disorders for seasonal variation in singletons and multiple births separately. This study aimed to determine whether the birth date distribution for individuals with autism spectrum disorders (ASD), including singletons and multiple births, differed from the general population. Two ASD case groups were studied: 907 singletons and 161 multiple births concordant for ASD. Two control groups were obtained from registered births of singletons and multiples. Results of the non-parametric time-series analyses, where day of birth was used, suggested there were three peaks in ASD singletons and ASD concordant multiple births. Roughly, the peaks were in April, June and October for singletons and about 2-4 weeks earlier in multiples. Results from multivariable Poisson regression, where month of birth was used, indicated that ASD concordant multiple births in males tended to be higher than expected in March, May and September (with borderline statistical significance), but were 87% less in December (P < 0.05), as compared with January. Overall, the patterns of relative risk estimates from Poisson regression are similar to findings from the non-parametric time-series approach, but are not exactly congruent. It is important to note that indications of seasonality may be sensitive to the selection of time cut-points and therefore an arbitrary binning of time can either mask existing trends or falsely indicate the presence of a trend. The presence of seasonal trends in ASD singletons and concordant multiple births suggests a role for non-heritable factors operating during the pre- or perinatal period, even among cases with a genetic susceptibility.

Fetal mechanisms in neurodevelopmental disorders

Normal development of the central nervous system depends on complex, dynamic mechanisms with multiple spatial and temporal components during gestation. Neurodevelopmental disorders may originate during fetal life from genetic as well as intrauterine and extrauterine factors that affect the fetal-maternal environment. Fetal neurodevelopment depends on cell programs, developmental trajectories, synaptic plasticity, and oligodendrocyte maturation, which are variously modifiable by factors such as stress and endocrine disruption, exposure to pesticides such as chlorpyrifos and to drugs such as terbutaline, maternal teratogenic alleles, and premature birth. Current research illustrates how altered fetal mechanisms may affect long-term physiological and behavioral functions of the central nervous system more significantly than they affect its form, and these effects may be transgenerational. This research emphasizes the diversity of such prenatal mechanisms and the need to expand our understanding of how, when altered, they may lead to disordered development, the signs of which may not appear until long after birth.

Antibodies against fetal brain in sera of mothers with autistic children

Serum antibodies in 100 mothers of children with autistic disorder (MCAD) were compared to 100 age-matched mothers with unaffected children (MUC) using as antigenic substrates human and rodent fetal and adult brain tissues, GFAP, and MBP. MCAD had significantly more individuals with Western immunoblot bands at 36 kDa in human fetal and rodent embryonic brain tissue. The density of bands was greater in fetal brain at 61 kDa. MCAD plus developmental regression had greater reactivity against human fetal brain at 36 and 39 kDa. Data support a possible complex association between genetic/metabolic/environmental factors and the placental transfer of maternal antibodies in autism.

Developmental regression and autism reported to the Vaccine Adverse Event Reporting System

We report demographic and clinical characteristics of children reported to the US Vaccine Adverse Event Reporting System (VAERS) as having autism or another developmental disorder after vaccination. We completed 124 interviews with parents and reviewed medical records for 31 children whose records contained sufficient information to evaluate the child's developmental history. Medical record review indicated that 27 of 31 (87%) children had autism/ASD and 19 (61.3%) had evidence of developmental regression (loss of social, language, or motor skills). The proportion of VAERS cases of autism with regression was greater than that reported in population-based studies, based on the subset of VAERS cases with medical record confirmation. This difference may reflect preferential reporting to VAERS of autism with regression. In other respects, the children in this study appear to be similar to other children with autism. Further research might determine whether the pathogenesis of autism with developmental regression differs from that of autism without regression.

Behaviors associated with fever in children with autism spectrum disorders

OBJECTIVE

Clinical case reports have suggested that the behaviors of children with autism spectrum disorders may improve with fever. The purpose of this study was to investigate the effect of illness on behaviors of children with autism spectrum disorders. Understanding the role of fever, if any, may be informative regarding causative mechanisms of and treatment opportunities for autism.

METHODS

We conducted a prospective study of 30 children (aged 2-18 years) with autism spectrum disorders during and after an episode of fever. Parent responses to the Aberrant Behavior Checklist were collected during fever (body temperature > or = 38.0 degrees C/100.4 degrees F), when fever had abated and the child was asymptomatic, and when the child had been fever-free for 7 days. Data were compared with those collected from parents of 30 age-, gender-, and language skills-matched afebrile children with autism spectrum disorders during similar time intervals.

RESULTS

Fewer aberrant behaviors were recorded for febrile patients on the Aberrant Behavior Checklist subscales of irritability, hyperactivity, stereotypy, and inappropriate speech compared with control subjects. Per expectation, lethargy scores were greater during fevers, and all improvements were transient. Data from patients with fever were stratified on variables related to illness severity. In the majority of these subgroup comparisons, the data suggested that effects from fever persisted in the less sick patients as well as in those with more severe illness.

CONCLUSIONS

We documented behavior change among children with autism spectrum disorders during fever. The data suggest that these changes might not be solely the byproduct of general effects of sickness on behavior; however, more research is needed to prove conclusively fever-specific effects and elucidate their underlying biological mechanisms (possibly involving immunologic and neurobiological pathways, intracellular signaling, and synaptic plasticity).

Neuroinflammation and behavioral abnormalities after neonatal terbutaline treatment in rats: implications for autism

Autism is a neurodevelopmental disorder presenting before 3 years of age with deficits in communication and social skills and repetitive behaviors. In addition to genetic influences, recent studies suggest that prenatal drug or chemical exposures are risk factors for autism. Terbutaline, a beta2-adrenoceptor agonist used to arrest preterm labor, has been associated with increased concordance for autism in dizygotic twins. We studied the effects of terbutaline on microglial activation in different brain regions and behavioral outcomes in developing rats. Newborn rats were given terbutaline (10 mg/kg) daily on postnatal days (PN) 2 to 5 or PN 11 to 14 and examined 24 h after the last dose and at PN 30. Immunohistochemical studies showed that administration of terbutaline on PN 2 to 5 produced a robust increase in microglial activation on PN 30 in the cerebral cortex, as well as in cerebellar and cerebrocortical white matter. None of these effects occurred in animals given terbutaline on PN 11 to 14. In behavioral tests, animals treated with terbutaline on PN 2 to 5 showed consistent patterns of hyper-reactivity to novelty and aversive stimuli when assessed in a novel open field, as well as in the acoustic startle response test. Our findings indicate that beta2-adrenoceptor overstimulation during an early critical period results in microglial activation associated with innate neuroinflammatory pathways and behavioral abnormalities, similar to those described in autism. This study provides a useful animal model for understanding the neuropathological processes underlying autism spectrum disorders.

Maternal antibrain antibodies in autism

Autism is a neurodevelopmental disorder of prenatal onset that is behaviorally defined. There is increasing evidence for systemic and neuroimmune mechanisms in children with autism. Although genetic factors are important, atypical prenatal maternal immune responses may also be linked to the pathogenesis of autism. We tested serum reactivity in 11 mothers and their autistic children, maternal controls, and several groups of control children, to prenatal, postnatal, and adult rat brain proteins, by immunoblotting. Similar patterns of reactivity to prenatal (gestational day 18), but not postnatal (day 8) or adult rat brain proteins were identified in autistic children, their mothers, and children with other neurodevelopmental disorders, and differed from mothers of normal children, normal siblings of children with autism and normal child controls. Specific patterns of antibody reactivity were present in sera from the autism mothers, from 2 to 18 years after the birth of their affected children and were unrelated to birth order. Immunoblotting using specific antigens for myelin basic protein (MBP) and glial acidic fibrillary protein (GFAP) suggests that these proteins were not targets of the maternal antibodies. The identification of specific serum antibodies in mothers of children with autism that recognize prenatally expressed brain antigens suggests that these autoantibodies could cross the placenta and alter fetal brain development.

beta2-Adrenergic receptor gene variants and risk for autism in the AGRE cohort

The beta2-adrenergic receptor is part of the catecholamine system, and variants at two polymorphic sites in the gene coding for the receptor (ADRB2) confer increased activity. Overstimulation of this receptor may alter brain development, and has been linked to autism in non-identical twins. The objective of this study was to determine whether alleles in ADRB2 are associated with diagnosis of autism in the Autism Genetic Resource Exchange (AGRE) population. Three hundred and thirty-one independent autism case-parent trios were included in the analysis. Subjects were genotyped at activity-related polymorphisms rs1042713 (codon 16) and rs1042714 (codon 27). Association between autism and genotypes at each polymorphic site was tested using genotype-based transmission disequilibrium tests, and effect modification by family and pregnancy characteristics was evaluated. Sensitivity to designation of the proband in each family was assessed by performing 1000 repeats of the analysis selecting affected children randomly. A statistically significant OR of 1.66 for the Glu27 homozygous genotype was observed. Increased associations with this genotype were observed among a subset of Autism Diagnostic Observation Schedule confirmed cases and a subset reporting experience of pregnancy-related stressors. In conclusion, the Glu27 allele of the ADRB2 gene may confer increased risk of autism and shows increased strength with exposure to pregnancy related stress.

HLA-DR4 in families with autism

Autoimmune disorders are observed with increased frequency among parents of individuals with autism, particularly mothers. Because there is evidence supporting an association between autoimmune disorders and specific alleles of the human leukocyte antigen (HLA) system, we examined HLA types and subtypes in families with autism. Two groups were studied: 16 families selected from a geographically defined area in eastern Tennessee have males with a diagnosis of autism; and 33 families selected across all regions in the United States have multiple males having autism diagnosis. The HLA-DR4 frequencies of mothers, fathers, and children in these two groups were compared with a reference series of 475 normal, unrelated Caucasians. Results of HLA typing indicated that mothers and their sons in the geographically defined group had a significantly higher frequency of DR4 than normal control subjects (odds ratio = 5.54, 95% confidence interval = 1.74-18.67 and odds ratio = 4.20, 95% confidence interval = 1.37-13.27, respectively). No significant difference in the distribution of HLA alleles was evident between the United States-all region group and control subjects. Findings of this study are consistent with a hypothesis that prenatal maternal-fetal immune interaction can affect fetal brain development in a population residing in a geographically defined region. Such immune interactions may involve HLA and related genes in both genetic and epigenetic mechanisms during pregnancy.

Plasma serotonin in autism

Serotonin is necessary for normal fetal brain development. Administration of serotonin inhibitors to pregnant rats results in offspring with abnormal behaviors, brain morphology, and serotonin receptor numbers. Low maternal plasma serotonin may contribute to abnormal brain development in autism. In this study, plasma serotonin levels in autism mothers and control mothers of typically developing children were compared, and plasma serotonin levels in children with autism (n = 17) and their family members were measured. Plasma serotonin levels in autism mothers were significantly lower than in mothers of normal children (P = 0.002). Plasma serotonin levels correlated between autism mothers and their children, but differed between autistic children and their fathers (P = 0.028) and siblings (P = 0.063). Low maternal plasma serotonin may be a risk factor for autism through effects on fetal brain development.

Antibrain antibodies in children with autism and their unaffected siblings

Serum autoantibodies to human brain, identified by ELISA and Western immunoblotting, were evaluated in 29 children with autism spectrum disorder (22 with autistic disorder), 9 non-autistic siblings and 13 controls. More autistic subjects than controls had bands at 100 kDa in caudate, putamen and prefrontal cortex (p<0.01) as well as larger peak heights of bands at 73 kDa in the cerebellum and cingulate gyrus. Both autistic disorder subjects and their matched non-autistic siblings had denser bands (peak height and/or area under the curve) at 73 kDa in the cerebellum and cingulate gyrus than did controls (p<0.01). Results suggest that children with autistic disorder and their siblings exhibit differences compared to controls in autoimmune reactivity to specific epitopes located in distinct brain regions.

Developmental regression and mitochondrial dysfunction in a child with autism

Autistic spectrum disorders can be associated with mitochondrial dysfunction. We present a singleton case of developmental regression and oxidative phosphorylation disorder in a 19-month-old girl. Subtle abnormalities in the serum creatine kinase level, aspartate aminotransferase, and serum bicarbonate led us to perform a muscle biopsy, which showed type I myofiber atrophy, increased lipid content, and reduced cytochrome c oxidase activity. There were marked reductions in enzymatic activities for complex I and III. Complex IV (cytochrome c oxidase) activity was near the 5% confidence level. To determine the frequency of routine laboratory abnormalities in similar patients, we performed a retrospective study including 159 patients with autism (Diagnostic and Statistical Manual of Mental Disorders-IV and Childhood Autism Rating Scale) not previously diagnosed with metabolic disorders and 94 age-matched controls with other neurologic disorders. Aspartate aminotransferase was elevated in 38% of patients with autism compared with 15% of controls (P <.0001). The serum creatine kinase level also was abnormally elevated in 22 (47%) of 47 patients with autism. These data suggest that further metabolic evaluation is indicated in autistic patients and that defects of oxidative phosphorylation might be prevalent.

Immunity, neuroglia and neuroinflammation in autism

Autism is a complex neurodevelopmental disorder of early onset that is highly variable in its clinical presentation. Although the causes of autism in most patients remain unknown, several lines of research support the view that both genetic and environmental factors influence the development of abnormal cortical circuitry that underlies autistic cognitive processes and behaviors. The role of the immune system in the development of autism is controversial. Several studies showing peripheral immune abnormalities support immune hypotheses, however until recently there have been no immune findings in the CNS. We recently demonstrated the presence of neuroglial and innate neuroimmune system activation in brain tissue and cerebrospinal fluid of patients with autism, findings that support the view that neuroimmune abnormalities occur in the brain of autistic patients and may contribute to the diversity of the autistic phenotypes. The role of neuroglial activation and neuroinflammation are still uncertain but could be critical in maintaining, if not also in initiating, some of the CNS abnormalities present in autism. A better understanding of the role of neuroinflammation in the pathogenesis of autism may have important clinical and therapeutic implications.

beta2-adrenergic receptor activation and genetic polymorphisms in autism: data from dizygotic twins

Gestational and genetic factors can contribute to autism during infancy and early childhood through their effects on fetal brain development. Previous twin studies have shown strong genetic components for the development of autism, a disorder that can have multiple causes. We investigated the effects of prenatal overstimulation of the beta2-adrenergic receptor in dizygotic twins who were exposed to terbutaline, a selective beta2-adrenergic receptor agonist used to treat premature labor, as a gestational factor. As a possible genetic mechanism, we studied two beta2-adrenergic receptor polymorphisms in twins from whom DNA was available: glycine substitution at codon 16 (16G) and glutamic acid substitution at codon 27 (27E), which show diminished desensitization in vivo compared with the wild-type receptor. Continuous terbutaline exposure for 2 weeks or longer was associated with increased concordance for autism spectrum disorders in dizygotic twins (relative risk = 2.0), with a further increase in the risk for male twins with no other affected siblings (relative risk = 4.4). A significant association was found between the presence of 16G and 27E polymorphisms in autistic patients compared with population controls (P = .006). Prenatal overstimulation of the beta2-adrenergic receptor by terbutaline or by increased signaling of genetic polymorphisms of the beta2-adrenergic receptor that have diminished desensitization can affect cellular responses and developmental programs in the fetal brain, leading to autism.

Cerebrospinal fluid and serum markers of inflammation in autism

Systemic immune abnormalities have no known relevance to brain dysfunction in autism. In order to find evidence for neuroinflammation, we compared levels of sensitive indicators of immune activation: quinolinic acid, neopterin, and biopterin, as well as multiple cytokines and cytokine receptors, in cerebrospinal fluid and serum from children with autism, to control subjects with other neurologic disorders. In cerebrospinal fluid from 12 children with autism, quinolinic acid (P = 0.037) and neopterin (P = 0.003) were decreased, and biopterin (P = 0.040) was elevated, compared with control subjects. In sera from 35 persons with autism, among cytokines, only tumor necrosis factor receptor II was elevated compared with controls (P < 0.02). Decreased quinolinic acid and neopterin in cerebrospinal fluid are paradoxical and suggest dysmaturation of metabolic pathways and absence of concurrent infection, respectively, in autism. Alternatively, they may be produced by microglia but remain localized and not expressed in cerebrospinal fluid.

Neuroglial activation and neuroinflammation in the brain of patients with autism

Autism is a neurodevelopmental disorder characterized by impaired communication and social interaction and may be accompanied by mental retardation and epilepsy. Its cause remains unknown, despite evidence that genetic, environmental, and immunological factors may play a role in its pathogenesis. To investigate whether immune-mediated mechanisms are involved in the pathogenesis of autism, we used immunocytochemistry, cytokine protein arrays, and enzyme-linked immunosorbent assays to study brain tissues and cerebrospinal fluid (CSF) from autistic patients and determined the magnitude of neuroglial and inflammatory reactions and their cytokine expression profiles. Brain tissues from cerebellum, midfrontal, and cingulate gyrus obtained at autopsy from 11 patients with autism were used for morphological studies. Fresh-frozen tissues available from seven patients and CSF from six living autistic patients were used for cytokine protein profiling. We demonstrate an active neuroinflammatory process in the cerebral cortex, white matter, and notably in cerebellum of autistic patients. Immunocytochemical studies showed marked activation of microglia and astroglia, and cytokine profiling indicated that macrophage chemoattractant protein (MCP)-1 and tumor growth factor-beta1, derived from neuroglia, were the most prevalent cytokines in brain tissues. CSF showed a unique proinflammatory profile of cytokines, including a marked increase in MCP-1. Our findings indicate that innate neuroimmune reactions play a pathogenic role in an undefined proportion of autistic patients, suggesting that future therapies might involve modifying neuroglial responses in the brain.

Autism clinical trials: biological and medical issues in patient selection and treatment response

Biomedical measures are critical in the initial patient-screening and -selection phases of a clinical trial in autism and related disorders. These measures can also play an important role in the assessment and characterization of response and can provide an opportunity to study underlying etiologic and pathophysiologic processes. Thus, biomedical measures, including clinical laboratory analyses, metabolic screening, and chromosomal analysis, are used to screen for potential safety-related problems, to decrease biological and genetic heterogeneity, and to define subgroups. Neurobiological measures can be examined as possible predictors, modifiers or surrogates of therapeutic response, and adverse effects. Neurobiological research measures can also be used to study mechanisms and extent of drug action and to perform baseline and longitudinal investigations of possible pathophysiologic alterations. The potential utility and desirability of specific measures are considered and the general approach to choosing measures for incorporation is discussed.

Proton MR spectroscopic imaging in Pelizaeus-Merzbacher disease

BACKGROUND AND PURPOSE

Pelizeaus-Merzbacher disease (PMD) is a clinically and molecularly heterogeneous disorder linked to deletion, mutations, or duplication of the proteolipid protein (PLP1) gene locus at Xq22. The current study was conducted to characterize the results of proton MR spectroscopic (MRS) imaging in PMD.

METHODS

Three boys with PMD (one with the severe connatal form and two with a more mild clinical phenotype [spastic paraplegia type 2]). and three age-matched healthy control subjects (age range, 2-7 years) underwent MR and MRS imaging. All imaging was performed at 1.5 T. For MRS imaging, oblique-axial sections (thickness, 15 mm; intersection gap, 2.5 mm) were recorded parallel to the anterior commissure-posterior commissure line (TR/TE/NEX, 2300/272/1) with lipid and water suppression. Ratios of metabolite peak areas were calculated, and spectra were bilaterally evaluated.

RESULTS

Diffuse or focal reductions in N-acetylaspartate were observed in the affected white matter in all three cases. These reductions seemed to be consistent with axonal damage. In addition, mild increases in choline and creatine levels were observed; these may have been due to astrocytic changes.

CONCLUSION

Proton MRS imaging may be helpful in evaluating regional pathophysiologic abnormalities in PMD and in distinguishing PMD from other leukodystrophies, which exhibit different metabolic profiles.

New insights into the structure and function of fatty acid-binding proteins

Fatty acid-binding proteins (FABPs) are members of a superfamily of lipid-binding proteins, and occur intracellularly in vertebrates and invertebrates. This review presents recent findings on the diversity of these FABPs and their proposed roles in fatty acid (FA) metabolism and other cellular processes. Special attention is paid to the structural features of the different mammalian FABP types and the physiological role of these proteins in FA transport, cell growth and differentiation, cellular signalling, gene transcription and cytoprotection. Additionally, data on FABP knockout mice and the implication of FABP in medicine are discussed.

Fatty-acid-binding proteins do not protect against induced cytotoxicity in a kidney cell model

Intracellular accumulation of fatty acids (FAs) is a well-described consequence of renal ischaemia and may lead to lethal cell injury. Fatty-acid-binding proteins (FABPs) are small cytosolic proteins with high affinity for FAs. They may protect vital cellular functions by binding to and promoting the metabolism of FAs, thereby reducing their intracellular concentration. In this study we investigated the putative cytoprotective role of FABPs in a Madin-Darby canine kidney (MDCK) cell model for renal damage. We studied the effects of transfection with cDNA encoding heart FABP, adipocyte FABP or liver FABP on cytotoxicity induced by chemical anoxia or FAs. Transfection of MDCK type II cells with these cDNA types caused a 5-20-fold increase in FABP content, but did not change the rate or extent of palmitate uptake. After 1 h of incubation with KCN, all cell types showed reduced viability and cellular ATP content and an intracellular accumulation of non-esterified FAs. High extracellular concentrations of oleate, but not palmitate, caused a markedly decreased cell viability and cellular ATP content. Oleate accumulated in non-esterified form in these cells. Simultaneous addition of glucose ameliorated the damaging effects of KCN or oleate, indicating that glycolytic ATP could substitute for uncoupled oxidative phosphorylation. No significant differences in the effects of chemical anoxia or oleate were observed between non-transfected, mock-transfected and FABP-cDNA-transfected cells. Non-esterified FA accumulation was not reduced in any of the FABP-cDNA-transfected cell lines. In conclusion, our data do not provide evidence for a cytoprotective role of FABP in this kidney cell model.

Postmortem brain abnormalities of the glutamate neurotransmitter system in autism

BACKGROUND

Studies examining the brains of individuals with autism have identified anatomic and pathologic changes in regions such as the cerebellum and hippocampus. Little, if anything, is known, however, about the molecules that are involved in the pathogenesis of this disorder.

OBJECTIVE

To identify genes with abnormal expression levels in the cerebella of subjects with autism.

METHOD

Brain samples from a total of 10 individuals with autism and 23 matched controls were collected, mainly from the cerebellum. Two cDNA microarray technologies were used to identify genes that were significantly up- or downregulated in autism. The abnormal mRNA or protein levels of several genes identified by microarray analysis were investigated using PCR with reverse transcription and Western blotting. alpha-Amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA)- and NMDA-type glutamate receptor densities were examined with receptor autoradiography in the cerebellum, caudate-putamen, and prefrontal cortex.

RESULTS

The mRNA levels of several genes were significantly increased in autism, including excitatory amino acid transporter 1 and glutamate receptor AMPA 1, two members of the glutamate system. Abnormalities in the protein or mRNA levels of several additional molecules in the glutamate system were identified on further analysis, including glutamate receptor binding proteins. AMPA-type glutamate receptor density was decreased in the cerebellum of individuals with autism (p < 0.05).

CONCLUSIONS

Subjects with autism may have specific abnormalities in the AMPA-type glutamate receptors and glutamate transporters in the cerebellum. These abnormalities may be directly involved in the pathogenesis of the disorder.

Ligand specificity and conformational stability of human fatty acid-binding proteins

Fatty acid binding proteins (FABPs) are small cytosolic proteins with virtually identical backbone structures that facilitate the solubility and intracellular transport of fatty acids. At least eight different types of FABP occur, each with a specific tissue distribution and possibly with a distinct function. To define the functional characteristics of all eight human FABPs, viz. heart (H), brain (B), myelin (M), adipocyte (A), epidermal (E), intestinal (I), liver (L) and ileal lipid-binding protein (I-LBP), we studied their ligand specificity, their conformational stability and their immunological crossreactivity. Additionally, binding of bile acids to I-LBP was studied. The FABP types showed differences in fatty acid binding affinity. Generally, the affinity for palmitic acid was lower than for oleic and arachidonic acid. All FABP types, except E-FABP, I-FABP and I-LBP interacted with 1-anilinonaphtalene-8-sulphonic acid (ANS). Only L-FABP, I-FABP and M-FABP showed binding of 11-((5-dimethylaminonaphtalene-1-sulfonyl)amino)undecanoic acid (DAUDA). I-LBP showed increasing binding of bile acids in the order taurine-conjugated>glycine-conjugated>unconjugated bile acids. A hydroxylgroup of bile acids at position 7 decreased and at position 12 increased the binding affinity to I-LBP. The fatty acid-binding affinity and the conformation of FABP types were differentially affected in the presence of urea. Our results demonstrate significant differences in ligand binding, conformational stability and surface properties between different FABP types which may point to a specific function in certain cells and tissues. The preference of I-LBP (but not L-FABP) for conjugated bile acids is in accordance with a specific role in bile acid reabsorption in the ileum.

Double-blind, placebo-controlled study of amantadine hydrochloride in the treatment of children with autistic disorder

OBJECTIVE

To test the hypothesis that amantadine hydrochloride is a safe and effective treatment for behavioral disturbances--for example, hyperactivity and irritability--in children with autism.

METHOD

Thirty-nine subjects (intent to treat; 5-19 years old; IQ > 35) had autism diagnosed according to DSM-IV and ICD-10 criteria using the Autism Diagnostic Interview-Revised and the Autism Diagnostic Observation Schedule-Generic. The Aberrant Behavior Checklist-Community Version (ABC-CV) and Clinical Global Impressions (CGI) scale were used as outcome variables. After a 1-week, single-blind placebo run-in, patients received a single daily dose of amantadine (2.5 mg/kg per day) or placebo for the next week, and then bid dosing (5.0 mg/kg per day) for the subsequent 3 weeks.

RESULTS

When assessed on the basis of parent-rated ABC-CV ratings of irritability and hyperactivity, the mean placebo response rate was 37% versus amantadine at 47% (not significant). However, in the amantadine-treated group there were statistically significant improvements in absolute changes in clinician-rated ABC-CVs for hyperactivity (amantadine -6.4 versus placebo -2.1; p = .046) and inappropriate speech (-1.9 versus 0.4; p = .008). CGI scale ratings were higher in the amantadine group: 53% improved versus 25% (p = .076). Amantadine was well tolerated.

CONCLUSIONS

Parents did not report statistically significant behavioral change with amantadine. However, clinician-rated improvements in behavioral ratings following treatment with amantadine suggest that further studies with this or other drugs acting on the glutamatergic system are warranted. The design of these and similar drug trials in children with autistic disorder must take into account the possibility of a large placebo response.

Lamotrigine therapy for autistic disorder: a randomized, double-blind, placebo-controlled trial

In autism, glutamate may be increased or its receptors up-regulated as part of an excitotoxic process that damages neural networks and subsequently contributes to behavioral and cognitive deficits seen in the disorder. This was a double-blind, placebo-controlled, parallel group study of lamotrigine, an agent that modulates glutamate release. Twenty-eight children (27 boys) ages 3 to 11 years (M = 5.8) with a primary diagnosis of autistic disorder received either placebo or lamotrigine twice daily. In children on lamotrigine, the drug was titrated upward over 8 weeks to reach a mean maintenance dose of 5.0 mg/kg per day. This dose was then maintained for 4 weeks. Following maintenance evaluations, the drug was tapered down over 2 weeks. The trial ended with a 4-week drug-free period. Outcome measures included improvements in severity and behavioral features of autistic disorder (stereotypies, lethargy, irritability, hyperactivity, emotional reciprocity, sharing pleasures) and improvements in language and communication, socialization, and daily living skills noted after 12 weeks (the end of a 4-week maintenance phase). We did not find any significant differences in improvements between lamotrigine or placebo groups on the Autism Behavior Checklist, the Aberrant Behavior Checklist, the Vineland Adaptive Behavior scales, the PL-ADOS, or the CARS. Parent rating scales showed marked improvements, presumably due to expectations of benefits.

Assessment of neural cell adhesion molecule (NCAM) in autistic serum and postmortem brain

Studies have identified structural abnormalities in areas of the autistic brain, with a pattern suggesting that a neurodevelopmental anomaly took place. Neural cell adhesion molecule (NCAM), which is involved in development of the central nervous system, was previously shown to be decreased in the serum of autistic individuals. In the present study, we measured NCAM protein in the sera from controls, patients with autism, siblings of autistic patients, and individuals with other neurologic disorders, but found no significant differences. We also measured NCAM protein in autistic postmortem brain samples and found the longest isoform, NCAM-180, to be significantly decreased. In addition, we investigated the mRNA expression of NCAM in these brain samples using cDNA microarrays and RT-PCR. Results show that NCAM mRNA levels are not altered in autism.

Fatty acid-binding proteins of nervous tissue

Fatty acid-binding proteins (FABPs) are cytosolic 14-15 kDa proteins, which are supposed to be involved in fatty acid (FA) uptake, transport, and targeting. They may modulate FA concentration and in this way influence function of enzymes, membranes, ion channels and receptors, and gene expression and cellular growth and differentiation. Nine FABP types can be discerned with a specific tissue distribution. In spite of 30-70% amino acid sequence identity, they have a similar tertiary, beta-clam structure in which the FA is bound. Nervous tissue contains four FABP types with a distinct spatio-temporal distribution. Myelin (M)-FABP is only present in the peripheral nerves, brain (B)-FABP and epidermal (E)-FABP mainly in glial cells and neurons, respectively of pre- and perinatal brain, and heart (H)-FABP in adult brain. Possible functions of FABPs in the nervous system are discussed. Binding studies with a range of physiological FA showed no large differences between recombinant proteins of the four human FABP types in binding specificity and affinity, also not for polyunsaturated FA (PUFA). The transfer of FA from fixed liposomes to mitochondria was similarly promoted by the four types. A marked difference in conformational stability was observed with H-FABP > B-FABP > M-FABP > E-FABP. Surface epitopes of H-FABP showed reaction with anti-B-FABP antibodies, but no other cross-reactivity of FABP type and heterologous antibodies was observed. The functional significance of the distinct spatio-temporal pattern of the four FABP types remains to be elucidated.

Spin-system heterogeneities indicate a selected-fit mechanism in fatty acid binding to heart-type fatty acid-binding protein (H-FABP)

Recent advances in the characterization of fatty acid-binding proteins (FABPs) by NMR have enabled various research groups to investigate the function of these proteins in aqueous solution. The binding of fatty acid molecules to FABPs, which proceeds through a portal region on the protein surface, is of particular interest. In the present study we have determined the three-dimensional solution structure of human heart-type FABP by multi-dimensional heteronuclear NMR spectroscopy. Subsequently, in combination with data collected on a F57S mutant we have been able to show that different fatty acids induce distinct conformational states of the protein backbone in this portal region, depending on the chain length of the fatty acid ligand. This indicates that during the binding process the protein accommodates the ligand molecule by a "selected-fit" mechanism. In fact, this behaviour appears to be especially pronounced in the heart-type FABP, possibly due to a more rigid backbone structure compared with other FABPs, as suggested by recent NMR relaxation studies. Thus differences in the dynamic behaviours of these proteins may be the key to understanding the variations in ligand affinity and specificity within the FABP family.