Jonas Melke

Genetic and Functional Analyses of SHANK2 Mutations Suggest a Multiple Hit Model of Autism Spectrum Disorders

Autism spectrum disorders (ASD) are a heterogeneous group of neurodevelopmental disorders with a complex inheritance pattern. While many rare variants in synaptic proteins have been identified in patients with ASD, little is known about their effects at the synapse and their interactions with other genetic variations. Here, following the discovery of two de novo SHANK2 deletions by the Autism Genome Project, we identified a novel 421 kb de novo SHANK2 deletion in a patient with autism. We then sequenced SHANK2 in 455 patients with ASD and 431 controls and integrated these results with those reported by Berkel et al. 2010 (n = 396 patients and n = 659 controls). We observed a significant enrichment of variants affecting conserved amino acids in 29 of 851 (3.4%) patients and in 16 of 1,090 (1.5%) controls (P = 0.004, OR = 2.37, 95% CI = 1.23–4.70). In neuronal cell cultures, the variants identified in patients were associated with a reduced synaptic density at dendrites compared to the variants only detected in controls (P = 0.0013). Interestingly, the three patients with de novo SHANK2 deletions also carried inherited CNVs at 15q11–q13 previously associated with neuropsychiatric disorders. In two cases, the nicotinic receptor CHRNA7 was duplicated and in one case the synaptic translation repressor CYFIP1 was deleted. These results strengthen the role of synaptic gene dysfunction in ASD but also highlight the presence of putative modifier genes, which is in keeping with the “multiple hit model” for ASD. A better knowledge of these genetic interactions will be necessary to understand the complex inheritance pattern of ASD.

The serotonin reuptake inhibitor fluoxetine reduces sex steroid-related aggression in female rats: an animal model of premenstrual irritability?

The aggressive behavior displayed by some (but not all) female Wistar rats when an unfamiliar rat is being introduced into their home cage (the resident intruder paradigm) was found to be higher in non-receptive phases (metestrus, diestrus) than in the receptive phases (proestrus, estrus) of the estrus cycle, and effectively reduced by ovariectomy. When removal of the ovaries was followed by administration of estradiol and progesterone, in a regimen mimicking the normal cyclical release of these hormones, aggressive behavior was elicited, two days after estrus, in animals that had displayed aggressive behavior before ovariectomy, but not in those that had not. Short-term administration of a serotonin reuptake inhibitor (fluoxetine hydrochloride; 10 mg/kg, i.p.; 4–5 days) reduced both the aggressive behavior displayed during the diestrus phase by normally cycling rats, and the aggressive behavior elicited by administration of estradiol plus progesterone after ovariectomy. It is suggested that the aggressive behavior displayed by the female Wistar rat in the resident intruder paradigm may serve as an animal model of premenstrual dysphoria.

Mutation screening of melatonin-related genes in patients with autism spectrum disorders

BackgroundOne consistent finding in autism spectrum disorders (ASD) is a decreased level of the pineal gland hormone melatonin and it has recently been demonstrated that this decrease to a large extent is due to low activity of the acetylserotonin O-methyltransferase (ASMT), the last enzyme in the melatonin synthesis pathway. Moreover, mutations in the ASMT gene have been identified, including a splice site mutation, that were associated with low ASMT activity and melatonin secretion, suggesting that the low ASMT activity observed in autism is, at least partly, due to variation within the ASMT gene.MethodsIn the present study, we have investigated all the genes involved in the melatonin pathway by mutation screening of AA-NAT (arylalkylamine N-acetyltransferase), ASMT, MTNR1A, MTNR1B (melatonin receptor 1A and 1B) and GPR50 (G protein-coupled receptor 50), encoding both synthesis enzymes and the three main receptors of melatonin, in 109 patients with autism spectrum disorders (ASD). A cohort of 188 subjects from the general population was used as a comparison group and was genotyped for the variants identified in the patient sample.ResultsSeveral rare variants were identified in patients with ASD, including the previously reported splice site mutation in ASMT (IVS5+2T>C). Of the variants affecting protein sequence, only the V124I in the MTNR1B gene was absent in our comparison group. However, mutations were found in upstream regulatory regions in three of the genes investigated, ASMT, MTNR1A, and MTNR1B.ConclusionsOur report of another ASD patient carrying the splice site mutation IVS5+2T>C, in ASMT further supports an involvement of this gene in autism. Moreover, our results also suggest that other melatonin related genes might be interesting candidates for further investigation in the search for genes involved in autism spectrum disorders and related neurobehavioral phenotypes. However, further studies of the novel variants identified in this study are warranted to shed light on their potential role in the pathophysiology of these disorders.

Association between a polymorphism of the 5-HT2C receptor and weight loss in teenage girls.

Receptors of the 5-HT2C subtype are assumed to be involved in the influence of serotonin on food intake. A polymorphism in the coding region of the gene for this receptor, resulting in a cysteine to serine substitution, has been reported. Fifty-seven somatically healthy teenage girls displaying weight loss and 91 normal-weight girls of the same age, all recruited by means of a population-based screening study, were compared with respect to this polymorphism. Subjects in the weight loss group displayed a higher frequency of the serine allele than those in the comparison group (23.7% vs. 7.7%, p = .0001). Seventy-two percent of the weight loss girls fulfilled the diagnostic criteria of anorexia nervosa, whereas 28% did not; when these two groups were separately analyzed, both differed significantly from controls with respect to serine allele frequency. The results support the notion that the studied gene may be involved in the regulation of food intake in young women.

Serotonin transporter gene polymorphisms: Effect on serotonin transporter availability in the brain of suicide attempters

The efficacy of serotonin reuptake inhibitors in depression and anxiety disorders suggests the gene coding for the serotonin transporter (5-HTT), SLC6A4, as a candidate of importance for these conditions. Positive findings regarding associations between polymorphisms in SLC6A4 have been reported, indicating that these polymorphisms may influence anxiety-related personality traits, as well as the risk of developing depression and suicidality. Serotonin 5-HTT availability was assessed with single photon emission computed tomography (SPECT), using (123)I-beta-CIT as ligand, in a population of unmedicated male suicide attempters (n=9) and in matched controls (n=9). Two polymorphisms in SLC6A4 were assessed, including the 5-HTTLPR located in the promoter region and a variable number of tandem repeats (VNTR) polymorphism in intron 2 (STin2). In suicide attempters, but not in controls, low 5-HTT availability was associated with the S allele of 5-HTTLPR and with the 12 repeat allele of STin2. Data suggest that polymorphisms in SLC6A4 may influence the expression of the brain serotonin transporter in suicide attempters.

Angiotensin-related genes in patients with panic disorder.

Enhanced respiratory variability and decreased heart rate variability have repeatedly been observed in patients with panic disorder. Prompted by the notion that angiotensin may be involved in the control of respiration, heart rate variability, and anxiety‐like behavior, we investigated the putative association between polymorphisms in three angiotensin‐related genes and panic disorder—angiotensinogen (AGT), angiotensin converting enzyme (ACE), and angiotensin II (ANG II) receptor type 1 (ATr1) in 72 patients with panic disorder and 504 controls. Allele and genotype distribution of the ATr1 A1166C allele and the AGT M235T did not differ between patients and controls. With respect to the ACE I/D polymorphism, the I allele was found to be more frequent in male (χ2 = 8.042, df = 1, P = 0.005), but not female, panic disorder patients than in controls. The results of this investigation provide preliminary evidence for the suggestion that angiotensin‐related genes may be associated with panic disorder in men.

Association between a dinucleotide repeat polymorphism of the estrogen receptor alpha gene and personality traits in women.

Estrogens are known to play a key role in the regulation of various aspects of behavior. In order to study the potential contribution of genetic variation in the estrogen receptor (ER) alpha to specific personality traits, we investigated a repeat polymorphism in the ER alpha gene in 172 42-year-old women who had been assessed using the Karolinska Scales of Personality (KSP). Based on the hypothesis that there is a relationship between the length of a repeat polymorphism and gene function,1 the alleles were divided into two groups: short and long. In order to elucidate the possible influence of the ER alpha gene on the different aspects of personality measured by means of the KSP, the possible association between this gene and four different factors (‘neuroticism’, ‘psychoticism’, ‘non-conformity’, and ‘extraversion’) was analysed. ‘Neuroticism’, ‘psychoticism’, and ‘non-conformity’ all appeared to be associated with the ER alpha gene. After correction for multiple comparisons by means of permutation analysis, the associations with the factor ‘non-conformity’—including the subscales ‘indirect aggression’ and ‘irritability’—and the factor ‘psychoticism’—including the subscale ‘suspicion’—remained significant. The results suggest that the studied dinucleotide repeat polymorphism of the ER alpha gene may contribute to specific components of personality.

Lack of association between the BDNF Val66Met polymorphism and Parkinson's disease in a Swedish population.

Polymorphism and Parkinson’s Disease in a Swedish Population Anna Håkansson, MS, Jonas Melke, MS, Lars Westberg, BS, Haydeh Niazi Shahabi, MS, Silva Buervenich, PhD, Andrea Carmine, MS, Kjell Klingborg, MD, Maj-Britt Grundell, MD, Barbara Schulhof, MD, Björn Holmberg, MD, PhD, Jarl Ahlberg, MD, Elias Eriksson, PhD, Olof Sydow, MD, PhD, Lars Olson, PhD, Bo Johnels, MD, PhD, and Hans Nissbrandt, MD, PhD

Possible association between the androgen receptor gene and autism spectrum disorder

Autism is a highly heritable disorder but the specific genes involved remain largely unknown. The higher prevalence of autism in men than in women, in conjunction with a number of other observations, has led to the suggestion that prenatal brain exposure to androgens may be of importance for the development of this condition. Prompted by this hypothesis, we investigated the potential influence of variation in the androgen receptor (AR) gene on the susceptibility for autism. To this end, 267 subjects with autism spectrum disorder and 617 controls were genotyped for three polymorphisms in exon 1 of the AR gene: the CAG repeat, the GGN repeat and the rs6152 SNP. In addition, parents and affected siblings were genotyped for 118 and 32 of the cases, respectively. Case-control comparisons revealed higher prevalence of short CAG alleles as well as of the A allele of the rs6152 SNP in female cases than in controls, but revealed no significant differences with respect to the GGN repeat. Analysis of the 118 families using transmission disequilibrium test, on the other hand, suggested an association with the GGN polymorphism, the rare 20-repeat allele being undertransmitted to male cases and the 23-repeat allele being overtransmitted to female cases. Sequencing of the AR gene in 46 patients revealed no mutations or rare variants. The results lend some support for an influence of the studied polymorphisms on the susceptibility for autism, but argue against the possibility that mutations in the AR gene are common in subjects with this condition.

Association between the estrogen receptor beta gene and age of onset of Parkinson’s disease

The purpose of this study was to investigate the potential contribution of genetic variants in the estrogen receptor beta gene to the aetiology of Parkinsons disease (PD). Several lines of evidence from human and animal studies suggest a protective role for estrogen in PD. Recently the estrogen receptor beta subtype was reported to be an important mediator of estrogen actions in the nigrostriatal dopamine system. Two single nucleotide polymorphisms at position 1730 and 1082 in the ER beta gene were genotyped, using pyrosequencing, in 260 patients with PD and 308 controls recruited from the Swedish population. Neither of the two estrogen receptor beta polymorphisms was associated with an increased risk for PD. However, the G allele of the A1730G polymorphism was more frequent in patients with an early age of onset than in patients with a late age of onset of PD (P = 0.006). Patients carrying the GG genotype had an odds ratio of 2.2 for having an early onset of PD compared to non-carriers. In conclusion, our results indicate that genetic variation in the estrogen receptor beta gene may influence the age of onset of PD.