Repint of "Reframing autism as a behavioral syndrome and not a specific mental disorder: Implications of genetic and phenotypic heterogeneity".

Clinical and molecular genetics have advanced current knowledge on genetic disorders associated with autism. A review of diverse genetic disorders associated with autism is presented and for the first time discussed extensively with regard to possible common underlying mechanisms leading to a similar cognitive-behavioral phenotype of autism. The possible role of interactions between genetic and environmental factors, including epigenetic mechanisms, is in particular examined. Finally, the pertinence of distinguishing non-syndromic autism (isolated autism) from syndromic autism (autism associated with genetic disorders) will be reconsidered. Given the high genetic and etiological heterogeneity of autism, autism can be viewed as a behavioral syndrome related to known genetic disorders (syndromic autism) or currently unknown disorders (apparent non-syndromic autism), rather than a specific categorical mental disorder. It highlights the need to study autism phenotype and developmental trajectory through a multidimensional, non-categorical approach with multivariate analyses within autism spectrum disorder but also across mental disorders, and to conduct systematically clinical genetic examination searching for genetic disorders in all individuals (children but also adults) with autism.

Reframing autism as a behavioral syndrome and not a specific mental disorder: Implications of genetic and phenotypic heterogeneity.

Clinical and molecular genetics have advanced current knowledge on genetic disorders associated with autism. A review of diverse genetic disorders associated with autism is presented and for the first time discussed extensively with regard to possible common underlying mechanisms leading to a similar cognitive-behavioral phenotype of autism. The possible role of interactions between genetic and environmental factors, including epigenetic mechanisms, is in particular examined. Finally, the pertinence of distinguishing non-syndromic autism (isolated autism) from syndromic autism (autism associated with genetic disorders) will be reconsidered. Given the high genetic and etiological heterogeneity of autism, autism can be viewed as a behavioral syndrome related to known genetic disorders (syndromic autism) or currently unknown disorders (apparent non-syndromic autism), rather than a specific categorical mental disorder. It highlights the need to study autism phenotype and developmental trajectory through a multidimensional, non-categorical approach with multivariate analyses within autism spectrum disorder but also across mental disorders, and to conduct systematically clinical genetic examination searching for genetic disorders in all individuals (children but also adults) with autism.

Serotonin transporter promoter variants in autism: functional effects and relationship to platelet hyperserotonemia.

The well-replicated platelet hyperserotonemia of autism has stimulated interest in serotonin (5-HT) in autism. We have examined the effects of the serotonin transporter gene (5-HTT, locus SLC6A4) promoter polymorphism (5-HTTLPR) on platelet 5-HT physiology in autism. Platelet 5-HT uptake rates and affinities (V(max) and K(m)), uptake site densities (B(max)) and 5-HT levels were examined in 31 French individuals with autism genotyped with respect to the 5-HTTLPR. Platelet 5-HT uptake and 5-HT levels were measured using HPLC; uptake sites were determined by radioligand binding. A 1.5-fold increased rate (V(max)) of platelet 5-HT uptake was observed in ll genotype individuals compared to those with ls and ss genotypes (Mann- Whitney U-test, P = 0.022). However, no significant relationship was observed between genotype and uptake site density (U-test, P = 0.51). Although median levels of platelet 5-HT in platelet-rich plasma were higher in the ll group, only trend level significance was observed (U-test, P= 0.069); platelet 5-HT content measured in whole blood was similar across genotypes. Uptake rates were well correlated with B(max) values (r = 0.66, P = 0.002); correlations between uptake and platelet 5-HT levels and between B(max) values and 5-HT levels were somewhat lower. While 5-HTTLPR alleles had an appreciable effect on platelet 5-HT uptake rates, effects on 5-HT levels and uptake site density were smaller or absent. Based on these preliminary data and prior studies of allele frequencies, we conclude that the 5-HTTLPR is not a major determinant of the group mean platelet serotonin elevation seen in autism. However, a role for increased uptake in the hyperserotonemia of autism can not be ruled out. In addition, it appears that studies of platelet 5-HT measures in autism and other disorders should take account of the effects of 5-HTTLPR genotype on 5-HT uptake

Letter to the editor: Chronicle for an orphan trait: comment on Hofer, Shair, Masmela, & Brunelli, "Developmental effects of selective breeding for an infantile trait: the rat pup ultrasonic isolation call".

Hofer, Brunelli, Shair, and Masmela (2001) examined several behavioral and physiological measures in low, high, and unselected lines obtained from a divergent selection for ultrasound production (USP) in young rats. Although the response to selection was clear-cut, few correlated responses appeared. This surprising result could be explained by two reasons. USP has polygenic correlates in this population, and most of the chromosomal regions that are linked with these measures only contribute to a small part of the genetic variance. Therefore, correlated responses to selection might exist, but the common genetic variance between the trait under selection and the indirectly selected trait is too small to be detected by a selective breeding strategy.

Sensory and motor development in mice: genes, environment and their interactions.

Sensory and motor developmental tests were designed to characterize spontaneous mutations in rodents. These tests are currently used to investigate developmental abnormalities associated with gene overexpression or gene targeting in mice. Here, we present an overview of our studies focused on 15 tests designed to measure sensory and motor development from birth to weaning in mice. Psychometric characteristics and factorial structure of these measures are considered first. The genetic correlates of these measures obtained with neurological mutants and gene mapping are compared. As a general rule, the contribution of genotype to the phenotypic variance of sensory and motor measures of development is low, inviting exploration of other sources of variation. Results from ovary transplantation, embryo transfer and fostering methods indicate that different components of maternal environment (cytoplasmic, uterine or postnatal) contribute to the behavioral phenotype. Although more difficult to detect, interactions between genotype and environment are involved.

Quantitative trait locus mapping: fishing strategy or replicable results?

Genomewide scan, as shown by recently published linkage studies on the behavior of mice or in psychiatry, provides evidence for replicated quantitative trait loci (QTL). Several studies of Alzheimer's disease have demonstrated the promise of moving from clinical diagnoses to biological signs for psychiatric investigations. Empirical studies also demonstrate that genetic background, differences in environment, epistatic effects, and definition of the phenotype (including psychiatric diagnosis) all actively contribute to limit the duplication of QTL.

Role of the serotonin transporter gene in the behavioral expression of autism.

The promoter polymorphism of the serotonin transporter gene (HTT, locus SLC6A4) is of special interest in autism given the well-replicated platelet hyperserotonemia of autism, treatment effects of serotonin reuptake inhibitors, and the role of serotonin in limbic functioning and neurodevelopment. Parent-offspring transmission of the long (l) and short (s) alleles of the deletion/insertion polymorphism in the HTT promoter region was examined in families of 71 children with autism using the transmission test for linkage disequilibrium (TDT). Transmission of HTT promoter alleles did not differ between probands with autism and their unaffected siblings. However, allelic transmission in probands was dependent upon severity of impairments in the social and communication domains, with greater s allele transmission in severely impaired individuals and greater l transmission in mild/moderately impaired individuals. This relationship between HTT promoter alleles and severity of autistic impairment was also seen when ratings of social and communication behaviors were compared across genotypes. The data indicate that HTT promoter alleles by themselves do not convey risk for autism, but, rather, modify the severity of autistic behaviors in the social and communication domains. The results require replication and, given the size of the groups and subgroups examined, must be considered still preliminary. The results suggest that future research on the genetics of autism should carefully assess each of the major behavioral domains and seriously consider the possible role of modifying loci.

Genetic architecture of testis and seminal vesicle weights in mice.

Comparisons across 13 inbred strains of laboratory mice for reproductive organ (paired seminal vesicles and paired testes) weights indicated a very marked contrast between the C57BL/6By and NZB/BINJ mice. Subsequently these strains were selected to perform a quantitative genetic analysis and full genome scan for seminal vesicle and testis weights. An F(2) population was generated. The quantitative genetic analyses indicated that each was linked to several genes. Sixty-six short sequences for length polymorphism were used as markers in the wide genome scan strategy. For weight of paired testes, heritability was 82.3% of the total variance and five QTL contributed to 72.8% of the total variance. Three reached a highly significant threshold (>4.5) and were mapped on chromosome X (LOD score 9.11), chromosome 4 (LOD score 5.96), chromosome 10 (LOD score 5.81); two QTL were suggested: chromosome 13 (LOD score 3.10) and chromosome 18 (LOD score 2.80). Heritability for weight of seminal vesicles was 50.7%. One QTL was mapped on chromosome 4 (LOD score 9.21) and contributed to 24.2% of the total variance. The distance of this QTL to the centromere encompassed the distance of the QTL linked with testicular weight on chromosome 4, suggesting common genetic mechanisms as expected from correlations in the F(2). Both testis and seminal vesicle weights were associated with a reduction in the NZB/BINJ when this strain carried the Y(NPAR) from CBA/H whereas the Y(NPAR) from NZB/BINJ in the CBA/H strain did not modify reproductive organ weights, indicating that the Y(NPAR) interacts with the non-Y(NPAR) genes. The effects generated by this chromosomal region were significant but small in size.

Loss of aggression, after transfer onto a C57BL/6J background, in mice carrying a targeted disruption of the neuronal nitric oxide synthase gene.

Phenotypic differences among mice with disrupted genes and those with wild-type alleles have not provided the necessary evidence for desired gene/phenotype correlations. These differences could be due to "passenger genes" from the donor 129 strains that are used to produce stem cells. Three variations of attack behavior were measured, using mice carrying a disruption of the neural nitric oxide synthase gene. In the first population, the disrupted gene had been maintained on a mixed background including C57BL/6J and 129 alleles. We have developed a second population in which the disrupted gene was transferred onto a C57BL/6J background during five backcross generations. On the mixed C57BL/6J-129 background, mice homozygous for disrupted Nos1 alleles attacked more frequently, had shorter attack latencies, and presented a greater number of attacks than mice carrying nondisrupted alleles. On the C57BL/6J background, no significant difference persisted between the carriers of the disrupted gene and their noncarrier siblings. The noncarriers on the mixed C57BL/6J-129 background, and the carriers or noncarriers on the C57BL/6J background, did not differ from C57BL/6J. The frequency of attacking males was identical in the homozygous carriers of the disrupted gene, in the mixed C57BL/6J-129 background, and in the 129/SvPas, which approximates the 129/SvJae strain from which the stem cells were derived to produce the disrupted Nos1 gene. These results suggest that Nos1 disruption was not implicated in attack behavior. A possible passenger-gene effect from the 129 donor strain is discussed.

Genetic dissection of gustatory sensitivity to bitterness (sucrose octaacetate) in mice.

Genes implicated in consumption of a bitter compound, sucrose octaacetate (SOA), were investigated using a full genomic scanning strategy. For a 0.1 mM concentration, two QTL reached 5.8 and 6.5 lod scores on chromosomes 2 (77 cM) and 11 (14 cM), respectively. For a 1 mM concentration, the Soa linkage on chromosome 6 (58 cM, lod score 9.4) was replicated, and another QTL was found on chromosome 19 (15 cM, lod score 3.2). Candidacy of previously identified genes in the close vicinity of the peak of the QTL was examined.

Radial maze learning in two inbred mouse strains and their reciprocal congenics for the non-pseudoautosomal region of the Y chromosome.

The effect of the non-pseudoautosomal region of the Y chromosome on spatial learning in a radial maze task was examined in two inbred mouse strains, NZB and CBA/H, and their respective congenics for the Y(NPAR). Seven variables reflecting learning performance, learning strategy and lateralisation were measured. We found no substantial effect of the Y(NPAR) on radial maze learning, but modest influences on behavioral strategies. These findings are in agreement with previous results regarding the sizes of the intra- and infrapyramidal mossy fiber (IIPMF) terminal fields.

Genetic correlation between steroid sulfatase concentration and initiation of attack behavior in mice.

The pairing region of the X-Y chromosomes recombines at male meiosis. We previously found that offense behavior in male mice, measured by initiation of attack against a conspecific male, was linked to this region. Only one functional gene (coding for steroid sulfatase or Sts) is mapped on this region as of yet, suggesting that it could be a candidate for offense behavior. We estimated the genetic correlation between the concentration of STS protein in the liver and the initiation of attack behavior in 11 strains of inbred mice. The high correlation (close to reliability) coefficient of the behavioral phenotype indicates the implication of STS in offense behavior. Recent investigations have demonstrated the involvement of STS in neurosteroid biochemical pathways, and several lines of evidence indicate that neurosteroids interact with neurotransmitters. These conclusions and our present results support the hypothesis that sulfatation of steroids may be the prime mover of a complex network, including genes shown to be implicated in aggression by mutagenesis.

Preweanling sensorial and motor development in laboratory mice: quantitative trait loci mapping.

Chromosomal mapping of genes linked with 19 measures of sensorial, motor, and body weight development were investigated. Chromosomal mapping is the first step towards gene identification. When a genomic region is shown to be linked to a trait, it is possible to select a reduced number of candidate genes that have been previously mapped on this region. The involvement of every gene can be individually tested either by molecular (transgenesis, homologous recombination) or traditional methods (congenicity). Mapping was performed using 389 males and females from two inbred strains of laboratory mice C57BL/6By and NZB/BlNJ, their reciprocal F1s and F2s. Thirty-six Quantitative Trait Loci (QTL) were mapped, 12 reached the 3.13 lod score, being thus considered as confirmed. These QTL were tentatively labeled: Cliff Drop Aversion (Cliff Qtl), Geotaxia (Geot Qtl), Vertical Clinging (VertCling Qtl), Bar Holding with the 4 paws (BH4P Qtl), Age at Eyelid Opening (Aeyo Qtl), Visual Placing (Vispl Qtl), Startle Response (Start Qtl1, Start Qtl2), Body Weight at Day 10 in Males pooled with Females (Bwefmd10 Qtl), and Body Weight at Day 30 in males (Bwemd30 Qtl). For the majority of the developmental measures, the QTL that were mapped contributed little to the phenotypic variance, even when mitochondrial DNA contribution was included: Righting Response (12.7%), Cliff Drop Aversion (10%), Crossed Extensor Response (18.1%), Geotaxia (16.2%), Bar Holding Response for 10 s (12.1%), Bar Holding Response with 4 paws (8.1%), Vertical Clinging (9.3%), Vertical Climbing (5%), Startle Response (21.2%), Eyelid Opening (14.6%), Visual Placing (22%), Body Weight at Day 10 (27%), Body Weight at Day 15 in Females (52.5%), Body Weight at Day 15 in Males (17%), Body Weight at Day 30 in Females (42%), and Body Weight at Day 30 in Males (48%). A factorial analysis of the correlations between the measures of development did not provide evidence of a general factor. A general genetic factor of development was also rejected because few common genetic correlates were discovered for the 19 measures of development (Body Weight at Days 15 and 30 in Females on Chromosome 2, Eyelid Opening and Body Weight at Day 10 on Chromosome 5 and mitochondrial genome for five measures). Co-identification of genes, the function of which were previously known thanks to newly discovered QTL, should help to explain the function of QTL. Present data help to highlight candidate regions including several genes that could be candidates for the QTL function. Large confidence intervals were obtained as usual from the F2 intercrossed population. More stringent methods are suggested for more efficient co-identification.

Is mitochondrial DNA involved in mouse behavioral laterality?

The genetic effect of mitochondrial DNA (mtDNA) on behavioral laterality was investigated in a quartet of strains of laboratory mice congenic for mtDNA. The pattern of restriction of mtDNA differed in NZB/BINJ and CBA/H mice. Their respective congenics for mtDNA were developed until the 22nd generation. This quartet was tested under three independent conditions involving fore- and hind paw preference or performance (laterality tests) and body orientation. Evidence for the implication of mtDNA was observed on direction of laterality in two test conditions and on degree of laterality in the three test conditions.

Neuronal and behavioral differences between Mus musculus domesticus (C57BL/6JBy) and Mus musculus castaneus (CAST/Ei).

Previous studies have demonstrated that classical inbred strains of laboratory mice do not exhibit large genetic distances when simple sequence repeats (SSRs) are used to test for their polymorphisms whereas mice from wild origin exhibit high polymorphisms (more than 90%) for these sequence when compared with classical inbred strains of laboratory mice. The difference between Mus musculus castaneus and C57BL/6J reaches 98% and F1s male and female are fertile. These two properties pave the way for gene mapping derivating segregating generations between these strains. The phenotypical characteristics of Mus musculus castaneus have not been investigated, unfortunately. The first screening of Mus musculus castaneus and C57BL/6By was carried out for sensorial and motor development, spontaneous behavior in new environment, paw preference, maternal behavior, aggression in two different situations and time to learn escape in a water maze. Morphometry of hippocampus and weight of the male reproductive organs for measures that have been reported to be correlated with several of the examined behavior are also reported. The authors tested also reactivity to one drug (beta-CCM) revealing seizure proneness. The two strains differ for 69% of the reported measures. Comparison to other strains for the same measures obtained in the laboratory for identical tests with mice reared in identical situations provided the mean to compare Mus musculus castaneus with a large set of more or less traditional mice. This strain has the most extreme position for 80% of the comparisons.

Genetic selection of mouse lines differing in sensitivity to a benzodiazepine receptor inverse agonist.

Mice were selectively bred according to their sensitivity or their resistance to the convulsive effects of a 4-mg/kg dose of methyl beta-carboline-3-carboxylate (beta-CCM), a benzodiazepine (BZ) receptor inverse agonist. The selection proved to be easy, with a clear separation of the two lines, convulsing with short latencies or resistant, already at the first generation of selection. Selection of a third line of animals convulsing with long latencies did not succeed. 3H-Ro 15-1788 binding analysis provided evidence for a strong decrease in Bmax in the resistant line.

Murine steroid sulfatase gene expression in the brain during postnatal development and adulthood.

The microsomal enzyme steroid sulfatase (STS, E.C.3.1.6.2) plays a central function in the neurosteroid mode of action, since it is responsible for the switch between the sulfated and the free forms of steroids which have opposite effects. In this study, using an enzyme linked immunosorbent assay (ELISA) for the STS, we have investigated the brain expression of STS in mice during development. We confirm that STS is present in the brain as previously shown by the measurement of the enzymatic activity. At birth, the STS level is clearly higher than in adults. We observed differences between physiological stages in females brain. The STS level is the same in pregnant and non-pregnant females, whereas STS concentration dramatically increased after delivery and during lactation.

Vocalizations in newborn mice: genetic analysis.

Two kinds of vocalizations are produced by newborn mice: whistles (between 50 and 150 ms in length), having a narrow bandwidth in each strain that ranges from 30 to 90 kHz; and clicks, which are shorter (about 1 ms) and have a larger bandwidth. These vocalizations were individually recorded in 1-day-old pups from seven inbred strains of laboratory mice, at two temperatures (23 +/- 0.5 and 15 +/- 0.5 degrees C). The numbers of clicks and whistles were counted under these two conditions. Moreover, the length and frequencies at the beginning, apex, and end of the whistles were measured during the 15 degrees C condition. Correlations, including several components-additivity, epistasis (between homozygous loci), and maternal environment-were calculated between the characteristics of the whistles during the 15 degrees C condition. Clicks and whistles were also counted from 1 to 8 days of age during the 15 degrees C condition. The numbers of clicks and whistles were age dependent, with a decrease from day 1 to day 8 for the clicks and a consistent production of whistles. A quantitative genetic analysis was also performed on the 1-day-old pups from the Mendelian generations produced by the inbred strains most contrasting for the number of whistles produced in the cold condition: NZB/BINJ and CBA/H. The heterozygous genotype of the mother induced an increment of the number of whistles. Moreover, a significant part of the additive variance was suspected from the first design, and found with the second one, for this variable. Quantitative genetic analysis showed significant dominance and epistasis between homozygous loci and homozygous and heterozygous loci. This points to multigenic correlates for the number of whistles in this population. The significant additive values for all the variables recorded during the 15 +/- 0.5 degrees C condition and for the number of whistles produced during the 23 +/- 0.5 degrees C condition are compatible with an effect that indicates neither directional nor stabilizing selection. This result is examined in the light of the multichannel sensorial process implicated in maternal behavior in mice.

Hippocampal morphology in the inbred mouse strains NZB and CBA/H and their reciprocal congenics for the nonpseudoautosomal region of the Y chromosome.

The effects of the nonpseudoautosomal region of the Y chromosome (YNPAR) on hippocampal morphology have been investigated in the inbred mouse strains NZB/BINJ and CBA/H, using comparisons between the two parentals and their respective congenics N.H-YNPAR and H.N-YNPAR. Results obtained depend upon the hippocampal variable measured. YNPAR had no effect on the sizes of the stratum oriens, hilus, or mossy fiber terminal fields (both suprapyramidal and intra- and infrapyramidal). However, in interaction with the strain background, it affected the strata lacunosum-moleculare, radiatum, and pyramidale. Possible relationships among gene(s), mossy fiber terminal fields, and intermale aggression are discussed.