Autism and the broad autism phenotype: familial patterns and intergenerational transmission

Background

Features of the Broad Autism Phenotype (BAP) are disproportionately prevalent in parents of a child with autism, highlighting familial patterns indicative of heritability. It is unclear, however, whether the presence of BAP features in both parents confers an increased liability for autism. The current study explores whether the presence of BAP features in two biological parents occurs more frequently in parents of a child with autism relative to comparison parents, whether parental pairs of a child with autism more commonly consist of one or two parents with BAP features, and whether these features are associated with severity of autism behaviors in probands.

Method

Seven hundred eleven parents of a child with an autism spectrum disorder and 981 comparison parents completed the Broad Autism Phenotype Questionnaire. Parents of a child with autism also completed the Social Communication Questionnaire.

Results

Although parental pairs of a child with autism were more likely than comparison parental pairs to have both parents characterized by the presence of the BAP, they more commonly consisted of a single parent with BAP features. The presence of the BAP in parents was associated with the severity of autism behaviors in probands, with the lowest severity occurring for children of parental pairs in which neither parent exhibited a BAP feature. Severity did not differ between children of two affected parents and those of just one.

Conclusions

Collectively, these findings indicate that parental pairs of children with autism frequently consist of a single parent with BAP characteristics and suggest that future studies searching for implicated genes may benefit from a more narrow focus that identifies the transmitting parent. The evidence of intergenerational transmission reported here also provides further confirmation of the high heritability of autism that is unaccounted for by the contribution of de novo mutations currently emphasized in the field of autism genetics.     

Phenotypic and genetic correlations between evoked EEG/ERP measures during the response anticipation period of a delayed response task

We investigated the relationship between three electrophysiological indices of response anticipation in a spatial delayed response task with a low and high memory load manipulation: a slow cortical potential (SCP), theta desynchronization, and upper alpha synchronization. Individual differences in these three measures were examined in 531 adult twins and siblings. Heritability of the SCP at occipital-parietal leads varied from 30% to 43%. Heritability of upper alpha synchronization (35% to 65%) and theta desynchronization (31% to 50%) was significant at all leads. Theta desynchronization and upper alpha synchronization were significantly correlated ( r ∼43%), but SCP was not correlated with either. The effect of working memory load on all three measures was not heritable. Response anticipation reliably evokes an SCP, upper alpha synchronization and theta desynchronization, but variation in these measures reflects different (genetic) sources.     

Hydrogen peroxide-induced Ca2+ responses in CNS pericytes

A single nucleotide polymorphism (SNP) in the brain-derived neurotrophic factor (BDNF) gene Val66Met has been associated with depression. However, the relationship between this SNP and depression has been mixed, especially when comparing studies of child and adult depression. We examined whether Val66Met would predict depression differentially in mothers versus their daughters. We also examined whether rumination, the tendency to brood and repetitively think about negative information, might serve as a mediator in the path between genotype and depressive symptoms. Participants included 200 individuals (100 mother-daughter pairs) from a high-risk population. The BDNF Val66Met polymorphism was examined in DNA samples from the mothers and daughters, and measures of depressive symptoms and rumination were also obtained. Among the young adolescent girls (ages 10-14), the Val/Val genotype was associated with more depressive symptoms and higher rumination scores compared to the Val/Met genotype. Furthermore, rumination mediated the relationship between genotype and depressive symptoms. However, in the mothers with adult-onset depression the Val/Met genotype was associated with more depressive symptoms, and rumination again mediated the relationship between genotype and depression. Rumination may be an endophenotype in the pathway from the BDNF Val66Met polymorphism to depression. Future work should further explore this mechanism and pursue explanations for its effects at different times in development.     

White matter hyperintensities in affected and unaffected late teenage and early adulthood offspring of bipolar parents: A two-center high-risk study

Background

White matter hyperintensities (WMHs) are among the most replicated neuroimaging findings in bipolar disorder (BD). It is not clear whether these lesions are an artifact of comorbid conditions, or whether they are directly associated with the disorder, or even represent biological risk factor for BD.

Methods

To test whether WMHs meet criteria for an endophenotype of BD, we conducted a high-risk design study and recruited 35 affected, 44 unaffected relatives of bipolar probands (age range 15-30 years), matched by age and sex with 49 healthy controls without any personal or family history of psychiatric disorders. The presence of WMHs was determined from Fluid Attenuated Inversion Recovery (FLAIR) scans acquired on a 1.5 Tesla scanner using a validated semi-quantitative scale.

Results

We found mostly low grade WMHs in all groups. The proportion of WMH-positive subjects was comparable between the unaffected high-risk, affected familial and control groups.

Conclusion

White matter hyperintensities did not meet criteria for an endophenotype of BD. Bipolar disorder in young subjects without comorbid conditions was not associated with increased rate of WMHs.     

The P300 event-related brain potential as a neurobiological endophenotype for substance use disorders: a meta-analytic investigation

Endophenotypes are intermediate phenotypes on the putative causal pathway from genotype to phenotype and can aid in discovering the genetic etiology of a disorder. There are currently very few suitable endophenotypes available for substance use disorders (SUD). The amplitude of the P300 event-related brain potential is a possible candidate. The present study determined whether the P300 amplitude fulfils two fundamental criteria for an endophenotype: (1) an association with the disorder (disease marker), and (2) presence in unaffected biological relatives of those who have the disorder (vulnerability marker). For this purpose, two separate meta-analyses were performed. Meta-analysis 1 investigated the P300 amplitude in relation to SUD in 39 studies and Meta-analysis 2 investigated P300 amplitude in relation to a family history (FH+) of SUD in 35 studies. The findings indicate that a reduced P300 amplitude is significantly associated with SUD (d = 0.51) and, though to a lesser extent, with a FH+ of SUD (d = 0.28). As a disease maker, the association between reduced P300 amplitude and SUD is significantly larger for participants that were exclusively recruited from treatment facilities (d = 0.67) than by other methods (i.e., community samples and family studies; d = 0.45 and 0.32, respectively), and larger for abstinent SUD patients (d = 0.71) than for current substance users (d = 0.37). Furthermore, in contrast to FH+ males, a P300 amplitude reduction seems not to be present in FH+ females (d = −0.07). Taken together, these results suggest that P300 amplitude reduction can be both a useful disease and vulnerability marker and is a promising neurobiological endophenotype for SUD, though only in males. Implications and future directions are discussed.     

Voxel-based morphometric gray matter correlates of daytime sleepiness

We theorized the cognitive vulnerability factor featured in hopelessness theory [2] to be a novel endophenotype for depression. We investigated two possible genetic contributors to individual differences in cognitive vulnerability (and, in turn, depression): the BDNF gene and the COMT gene. Results showed that individuals (n = 95) with the BDNF Val⁶⁶ genotype had significantly greater levels of cognitive vulnerability than individuals with a BDNF Met⁶⁶ genotype. In addition, among individuals with high levels of cognitive vulnerability, those with the Val⁶⁶ genotype were significantly more likely than participants with a Met⁶⁶ genotype to experience increases in depressive symptoms when faced with increased stress. The COMT gene was not associated with cognitive vulnerability or risk for depression. Results support the use of the cognitive vulnerability factor featured in hopelessness theory as an endophenotype associated with depression as well as the role of the BDNF gene in a cognitive subtype of depression.     

Cognitive function in families with exceptional survival

The authors investigated whether cognitive function may be used as an endophenotype for longevity by assessing the cognitive performance of a family-based cohort consisting of 1380 individuals from 283 families recruited for exceptional survival in field centers in Boston, New York, Pittsburgh, and Denmark. Cognitive performance was assessed in the combined offspring of the Long Life Family Study (LLFS) probands and their LLFS siblings as compared with their spouses' cognitive performance. Our results indicate that the combined offspring of the LLFS probands and their siblings achieve significantly higher scores on both digit forward and backward tasks (p = 5 10^-5 and p = 8 10^-4 respectively) as well as on a verbal fluency task (p = 0.008) when compared with their spouse controls. No differences between groups were found for the other cognitive tests assessed. We conclude that LLFS family members in the offspring generation demonstrate significantly better performance on multiple tasks requiring attention, working memory, and semantic processing when compared with individuals without a family history of exceptional survival, suggesting that cognitive performance may serve as an important endophenotype for longevity.     

Endophenotyping in idiopathic adult onset cervical dystonia

Objective

Idiopathic adult onset cervical dystonia (IAOCD) is considered to be a partially penetrant autosomal dominant genetic condition. Dystonia may result from genetic and environmental factors. In this view, part of the physiology should be an endophenotype stemming from the genetic background. We assessed the most discriminative test to separate patients with IAOCD and healthy controls for further endophenotyping in non-affected 1st degree relatives.

Cognitive functioning in affected sibling pairs with ADHD: familial clustering and dopamine genes

Background:  This paper examines familiality and candidate gene associations of cognitive measures as potential endophenotypes in attention-deficit/hyperactivity disorder (ADHD).
Methods:  The sample consists of 540 participants, aged 6 to 18, who were diagnosed with ADHD from 251 families recruited for a larger genetic study of ADHD. All members of the family underwent psychiatric interviews and children were administered a large battery of cognitive tasks. Subjects were genotyped for several dopaminergic candidate genes (DAT1, DRD4, and DRD5).
Results:  Performance on measures of intelligence, working memory, and set-shifting had the highest sibling correlations and exhibited significant familial clustering. The 7-repeat allele of the dopamine receptor D4 (DRD4) gene was associated with poor performance on measures of intelligence, color naming, interference control, and working memory. There were no significant associations with DAT1 and DRD5.
Conclusions:  Sibling correlations, familial clustering and candidate gene associations provide strong support for verbal working memory as a candidate endophenotype for ADHD. More complex models of, and larger sample sizes for, genetic association with cognitive functions are encouraged for future study.     

Proton Magnetic Resonance Spectroscopy in Alcohol Use Disorders: A Potential New Endophenotype?

Background:  Current effort is directed at defining new classification schemes for alcohol use disorders (AUD) based on genetic/biological, physiological, and behavioral endophenotypes.
Methods:  We describe briefly findings of in vivo brain proton magnetic resonance spectroscopy (¹H MRS) studies in AUD and propose that they be further explored and expanded regarding their value as a potential endophenotype for AUD.
Results:  In vivo ¹H MRS, as part of the emerging field of "imaging genomics," may provide readily accessible, objective, functionally significant and region-specific neurobiological measures that successfully link genotypes to neurocognition and to psychiatric symptomatology in relatively small patient cohorts. We discuss several functional gene variants that may affect specific ¹H MRS-detectable metabolites and provide recent data from our own work that supports the view of genetic effects on metabolite measures.
Conclusions:  MRS-genetics research will not only offer clues to the functional significance and downstream effects of genetic differences in AUD, but, via monitoring and/or predicting the efficacy of pharmacological and behavioral interventions as a function of genotype, has the potential to influence future clinical management of AUD.