Genomic and epigenetic evidence for oxytocin receptor deficiency in autism.

BACKGROUND: Autism comprises a spectrum of behavioral and cognitive disturbances of childhood development and is known to be highly heritable. Although numerous approaches have been used to identify genes implicated in the development of autism, less than 10% of autism cases have been attributed to single gene disorders. METHODS: We describe the use of high-resolution genome-wide tilepath microarrays and comparative genomic hybridization to identify copy number variants within 119 probands from multiplex autism families. We next carried out DNA methylation analysis by bisulfite sequencing in a proband and his family, expanding this analysis to methylation analysis of peripheral blood and temporal cortex DNA of autism cases and matched controls from independent datasets. We also assessed oxytocin receptor (OXTR) gene expression within the temporal cortex tissue by quantitative real-time polymerase chain reaction (PCR). RESULTS: Our analysis revealed a genomic deletion containing the oxytocin receptor gene, OXTR (MIM accession no.: 167055), previously implicated in autism, was present in an autism proband and his mother who exhibits symptoms of obsessive-compulsive disorder. The proband's affected sibling did not harbor this deletion but instead may exhibit epigenetic misregulation of this gene through aberrant gene silencing by DNA methylation. Further DNA methylation analysis of the CpG island known to regulate OXTR expression identified several CpG dinucleotides that show independent statistically significant increases in the DNA methylation status in the peripheral blood cells and temporal cortex in independent datasets of individuals with autism as compared to control samples. Associated with the increase in methylation of these CpG dinucleotides is our finding that OXTR mRNA showed decreased expression in the temporal cortex tissue of autism cases matched for age and sex compared to controls. CONCLUSION: Together, these data provide further evidence for the role of OXTR and the oxytocin signaling pathway in the etiology of autism and, for the first time, implicate the epigenetic regulation of OXTR in the development of the disorder.See the related commentary by Gurrieri and Neri: http://www.biomedcentral.com/1741-7015/7/63.

An environmental approach to correcting iodine deficiency: supplementing iodine in soil by iodination of irrigation water in remote areas.

OBJECTIVE: Iodine deficiency disorders continue to be a severe problem in many parts of Central Asia, causing delayed mental development and cretinism in indigenous populations. In some areas, iodized salt has not succeeded in controlling this problem. In southern Xinjiang Province of China, we tried a new method of supplying iodine to rural populations by dripping potassium iodate into irrigation water canals. By this means iodine was distributed into soil, crops, animals and people. This proved feasible and cost effective; it reached all the people, required no medical expertise, required no continuing effort after the initial dripping, and had the important added benefit of improving livestock production. METHODS: We serially monitored iodine concentrations in soil, crops, animal products and human urine for several years after the last dripping. In a similar project in Inner Mongolia, total soil iodine was determined in addition. Here, iodine concentrations in soil, crops, animals and people have been monitored for 4 years after supplementation. RESULTS: After dripping, total iodine increased two-fold, while soluble iodine increased 4-5-fold. Iodine added to soil is available for more than 4 years after a single application. CONCLUSIONS: Potassium iodate added to soil appears to increase soluble iodine out of proportion to the amount added. This effect and the long persistence of dripped iodate in soil contribute to the efficacy and cost effectiveness of this method of iodine supplementation.

Lack of association between autism and SLC25A12.

OBJECTIVE: Autism has a strong, complex genetic component, most likely involving several genes. Multiple genomic screens have shown evidence suggesting linkage to chromosome 2q31-q33, which includes the SLC25A12 gene. Recently, an association between autism risk and two single nucleotide polymorphisms (SNPs) in SLC25A12 was reported. This study aimed to test for association in SLC25A12 in an independent data set of 327 families with autistic offspring. METHOD: The authors analyzed two SNPs that were significant in the previous study group, as well as seven additional SNPs within the gene. Association analyses for individual SNPs as well as haplotypes were performed. RESULTS: There was no evidence of an association between SLC25A12 and autism. CONCLUSIONS: These results suggest that SLC25A12 is not a major contributor to autism risk in these families.

Accelerated head growth in early development of individuals with autism.

Macrocephaly is one of the most consistent physical findings reported in autistic individuals. Previous studies attempted to determine if macrocephaly is associated with risk for autism. This study hypothesizes that an abnormal acceleration in head growth during early development, rather than macrocephaly, is associated with autism risk. To investigate this hypothesis, head circumference data were examined in 251 individuals from 82 multiplex (at least two individuals with autism) and 113 sporadic (no family history) families with autism. This examination included longitudinal measurements for 79 individuals. Nineteen percent of the original 251 individuals were found to have macrocephaly (head circumference >97%). Abnormal acceleration in head growth was defined as an increase of 25 or more percentile points in head circumference between two consecutive measurements. Thirty-five percent of individuals with multiple head circumference records had an abnormal increase in head circumference. Furthermore, autistic individuals with accelerated head growth in early childhood displayed higher levels of adaptive functioning and less social impairment. This study confirms the presence of abnormal acceleration in head growth during the first and second months of life in a subgroup of autistic individuals.

Analysis of the autism chromosome 2 linkage region: GAD1 and other candidate genes.

Autism has a strong and complex genetic component, involving several genes. Genomic screens, including our own, have shown suggestive evidence for linkage over a 20-30 cM region on chromosome 2q31-q33. Two subsequent reports showed that the linkage evidence increased in the subset of families with phrase speech delay (PSD), defined as onset of phrase speech later than 3 years of age. To further investigate the linkage in the presumptive candidate region, microsatellite markers in a 2 cM grid covering the interval from 164 to 203 cM were analyzed in 110 multiplex (2 or more sampled autism patients) families. A maximum heterogeneity LOD (HLOD) score of 1.54 was detected at D2S1776 (173 cM) in the overall dataset (dominant model), increasing to 1.71 in the PSD subset. While not conclusive, these data continue to provide suggestive evidence for linkage, particularly considering replication by multiple independent groups. Positive LOD scores extended over the entire region, continuing to define a broad candidate interval. Association studies were performed on several functional candidates mapping within the region. These included GAD1, encoding GAD67, whose levels are reduced in autopsy brain material from autistic subjects, and STK17B, ABI2, CTLA4, CD28, NEUROD1, PDE1A, HOXD1 and DLX2. We found no evidence for significant allelic association between autism and any of these candidates, suggesting that they do not play a major role in the genetics of autism or that substantial allelic heterogeneity at any one of these loci dilutes potential disease-allele association.

A lethal association of congenital apnea with brainstem tegmental necrosis.

We present a female with premature birth, polyhydramnios, congenital apnea, cranial nerve palsies, orofacial and limb anomalies. Neuroimaging revealed calcifications along the vental margin of the caudal fourth ventricle. Neuropathologic findings at postmortem examination were consistent with brainstem tegmental necrosis and olivary hypoplasia, a rare lethal entity that should be considered in the differential diagnosis of congenital apnea.

Factor analysis of restricted and repetitive behaviors in autism using the Autism Diagnostic Interview-R.

The current study examined the factor structure of restricted and repetitive behaviors (RRB) in children with autism. Factor extraction procedures of 12 items from the Autism Diagnostic Interview-Revised (ADI-R) were applied in N = 207 individuals with autism. Two interpretable factors were identified: Factor 1--repetitive sensory motor actions and Factor 2--resistance to change. There was a significant negative correlation between an index of level of adaptive functioning and Factor 1. Intraclass correlations were not significant for either factor in a subset of families with two or more siblings with autism (multiplex). No differences in scores were apparent for either factor when multiplex families and families containing only one affected individual with autism (singleton) were compared. RRB in autism are represented by two distinct factors which may reflect two separate groups within autism. Defining subgroups within autism will allow for reduction of clinical heterogeneity and enhance our ability to dissect the genetic etiology of this complex disorder.

Fluoxetine response in children with autistic spectrum disorders: correlation with familial major affective disorder and intellectual achievement.

One hundred and twenty-nine children, 2 to 8 years old, with idiopathic autistic spectrum disorder diagnosed by standard instruments (Childhood Austim Ratings Scale and Autism Diagnostic Observation Schedule) were treated with fluoxetine (0.15 to 0.5mg/kg) for 5 to 76 months (mean 32 to 36 months), with discontinuation trials. Response criteria are described. Family histories were obtained using the family history method in repeated interviews. Fluoxetine response, family history of major affective disorder, and unusual intellectual achievement, pretreatment language, and hyperlexia were used to define a coherent subgroup of autistic spectrum disorder. Statistical analyses were post hoc. Of the children, 22 (17%) had an excellent response, 67 (52%) good, and 40 (31%) fair/poor. Treatment age did not correlate with response. Fluoxetine response correlated robustly with familial major affective disorder and unusual intellectual achievement, and with hyperlexia in the child. Family history of bipolar disorder and of unusual intellectual achievement correlated strongly. Five children developed bipolar disorder during follow-up. Fluoxetine response, family history of major affective disorder (especially bipolar), unusual achievement, and hyperlexia in the children appear to define a homogeneous autistic subgroup. Bipolar disorder, unusual intellectual achievement, and autistic spectrum disorders cluster strongly in families and may share genetic determinants.

Mid-gestation right basal ganglia lesion: clinical observations in two children.

OBJECTIVE: To describe the neurobehavioral syndrome in two children with destruction of the right basal ganglia ostensibly from amniocentesis needle penetration at 17 weeks of gestation. BACKGROUND: Early-life unilateral lesions of the basal ganglia are rare and the resulting syndrome not described. METHODS: Both children had repeated clinical assessments, MRI and (18)F-fluorodeoxyglucose PET scans, and psychometric and achievement testing over 10 years. RESULTS: Right basal ganglia destruction was similar and virtually coextensive in both children; optic nerve and oculomotor dysfunction were disparate. One had a right temporal pole porencephalic cyst with anomalous overlying cortex. The clinical syndrome included left hemiparesis with distal spasticity and without hypotrophy; extraocular movement disorders; severe episodic disinhibition, impulsiveness, hitting reflexively, and extreme emotional lability. Outbursts of screaming and cursing resembled "sham rage." Both had mild intellectual retardation with competent language but poor nonverbal and visual-spatial abilities, visual memory, and daily living and socialization skills. CONCLUSIONS: The shared behavioral and cognitive syndrome is most reasonably attributed to the right basal ganglia lesions, which were complete and coextensive in both, whereas other lesions were partial, milder, and disparate. Early destruction of the right basal ganglia may preclude normal development of right hemisphere functions without evidence of plasticity and appears associated with intense disinhibition and impulsiveness of aggressive attack activities and with general lability and dyscontrol of emotion.

Effects of iodine supplementation during pregnancy on child growth and development at school age.

Growth and development of 207 children (49% males; mean age 5.4 years [SD 0.2], range 4 to 7.3 years whose mothers received iodine during pregnancy, and children who received iodine first in their 2nd year, were examined in 1996; 192 children (49% males; mean age 6.5 years [SD 0.2], range 5.8 to 6.9 years) whose mothers received iodine while pregnant were seen in 1998. Children were from the southern part of China's Xinjiang Province which has the lowest levels of iodine in water and soil ever recorded. Head circumference but not height was improved for those who received iodine during pregnancy (compared with those receiving iodine at age 2) and for those supplemented before the end of the 2nd trimester (relative to those supplemented during the 3rd trimester). Iodine before the 3rd trimester predicted higher psychomotor test scores for children relative to those provided iodine later in pregnancy or at 2 years. Results from the test for cognitive development resulted in trend only differences between those children supplemented during pregnancy versus later. The results address the question of when maternal iodine supplements should begin in public health programs world wide. Findings may be relevant to the treatment of maternal and newborn thyroid deficiency in industrialized countries, particularly for those infants delivered before the end of the second trimester.

No association between the WNT2 gene and autistic disorder.

Autistic disorder is a pervasive neurodevelopmental disorder characterized by deficits in language and social communication, as well as stereotyped patterns of behavior. Peak LOD scores from several genomic screening efforts indicate the presence of an autistic disorder susceptibility locus within the distal long arm of human chromosome 7 (7q31-q35). Wassink et al. [2001: Am J Med Genet 105:406-413] reported that WNT2, located at 7q31, influences genetic risk in autistic disorder. These findings were enhanced when examined in a subset of families with severe language impairment. WNT genes encode secreted growth factor-like proteins that participate in growth regulation, differentiation, and tumorigenesis. We tested for genetic association of two WNT2 variants in an independent data set of 135 singleton and 82 multiplex families. No significant association was found between autistic disorder and the WNT2 genotypes in either the overall data set or in the language-impaired subset of families. However, differences in allele frequencies of the 3' UTR single nucleotide polymorphism between the present population and that of Wassink et al. may account for the inability to detect association between WNT2 and autistic disorder in the present data set. We also screened the two reported autistic disorder mutations previously detected by Wassink et al. We did not identify any activating mutation in the coding region of the WNT2 gene. Thus, we conclude that activating mutations of the WNT2 gene are not a major contributor to the development of autistic disorder in these data.