Rare heterozygous genetic variants of NRXN and NLGN gene families involved in synaptic function and their association with neurodevelopmental disorders.

The interaction of neurexins (NRXNs) in the presynaptic membrane with postsynaptic cell adhesion molecules called neuroligins (NLGNs) is critical for this synaptic function. Impaired synaptic functions are emphasized in neurodevelopmental disorders to uncover etiological factors. We evaluated variants in NRXN and NLGN genes encoding molecules located directly at the synapse in patients with neuropsychiatric disorders using clinical exome sequencing and chromosomal microarray. We presented detailed clinical findings of cases carrying heterozygous NRXN1 (c.190C > T, c.1679C > T and two copy number variations [CNVs]), NRXN2 (c.808dup, c.1901G > T), NRXN3 (c.3889C > T), and NLGN1 (c.269C > G, c.473T > A) gene variants. In addition, three novel variants were identified in the NRXN1 (c.1679C > T), NRXN3 [c.3889C > T (p.Pro1297Ser)], and NLGN1 [c.473T > A (p.Ile158Lys)] genes. We emphasize the clinical findings of CNVs of the NRXN1 gene causing a more severe clinical presentation than single nucleotide variants of the NRXN1 gene in this study. We detected an NRXN2 gene variant (c.808dup) with low allelic frequency in two unrelated cases with the same diagnosis. We emphasize the importance of this variant for future studies. We suggest that NRXN2, NRXN3, and NLGN1 genes, which are less frequently reported than NRXN1 gene variants, may also be associated with neurodevelopmental disorders.

Association of ABCA13 Gene Variants with Autism Spectrum Disorder and Other Neuropsychiatric Disorders.

Introduction: Autism spectrum disorder (ASD) is a neuropsychiatric disorder characterized by impaired social skills and limited or repetitive behaviors. In this study, we investigated the role of the ABCA13 gene in the etiopathogenesis of ASD. Methods: Single-nucleotide variants were evaluated in 79 ASD patients (59 males +20 females) with no established genetic etiology associated with ASD using whole-exome sequencing/clinical exome sequencing method. Family segregation analysis was performed using Sanger sequencing. We presented the clinical and genetic findings of these cases and their parents in detail. Results: We presented 10 different ABCA13 gene variants in cases with ASD and 10 parents carrying the same ABCA13 gene variant. There of these variants were likely pathogenic and seven variants were classified as variant of uncertain significance. Our cases had a comorbidity rate for attention deficit hyperactivity disorder (ADHD) as 70%. Various types of neuropsychiatric symptoms and diagnoses were detected including ADHD, anxiety disorder, intellectual disability, delay in speech, and febrile convulsion among the parents. Conclusion: To date, very few variants have been reported in the ABCA13 gene. Our findings enrich the role of ABCA13 gene may play a common role in the landscape of neuropsychiatric disorders.

Clinical and Genetic Characteristics of Patients with Unexplained Intellectual Disability/Developmental Delay without Epilepsy.

Introduction: Global developmental delay (DD), intellectual disability (ID), and autism spectrum disorder (ASD) are mainly evaluated under the neurodevelopmental disorder framework. In this study, we aimed to determine the genetic diagnosis yield using step-by-step genetic analysis in 38 patients with unexplained ID/DD and/or ASD. Methods: In 38 cases (27 male, 11 female) with unexplained ID/DD and/or ASD, chromosomal microarray (CMA) analysis, clinical exome sequencing (CES), and whole-exome sequencing (WES) analysis were applied, respectively. Results: We found a diagnostic rate of only CMA analysis as 21% (8/38) presenting 8 pathogenic and likely pathogenic CNVs. The rate of patients diagnosed with CES/WES methods was 32.2% (10/31). When all pathogenic and likely pathogenic variants were evaluated, the diagnosis rate was 44.7% (17/38). A dual diagnosis was obtained in a case with 16p11.2 microduplication and de novo SNV. We identified eight novel variants: TUBA1A (c.787C>G), TMEM63A (c.334-2A>G), YY1AP1 (c.2051_2052del), ABCA13 (c.12064C>T), ABCA13 (c.13187G>A), USP9X (c.1189T>C), ANKRD17 (c.328_330dup), and GRIA4 (c.17G>A). Conclusion: We present diagnostic rates of a complementary approach to genetic analysis (CMA, CES, and WES). The combined use of genetic analysis methods in unexplained ID/DD and/or ASD cases has contributed significantly to diagnosis rates. Also, we present detailed clinical characteristics to improve genotype-phenotype correlation in the literature for rare and novel variants.

Distinct Autism Spectrum Disorder Phenotype and Hand-Flapping Stereotypes: Two Siblings with Novel Homozygous Mutation in TRAPPC9 Gene and Literature Review.

Objective: Pathogenic mutations of the TRAPPC9 gene are the rare genetic causes of autosomal recessive intellectual disability (ID). There are several features that are not fully penetrant such as microcephaly, dysmorphic facial features, obesity, autism spectrum disorder (ASD), attention-deficit hyperactivity disorder (ADHD), and brain abnormalities in TRAPPC9 mutations. Methods: We performed whole-exome sequencing to evaluate 2 Turkish siblings with ASD and ID born to healthy and consanguineous parents. Parental samples were also analyzed, specifically targeting variants detected in these patients. Results: We present a novel homozygous mutation in the TRAPPC9 gene, c.484G>T (p.Glu162Ter). Additionally, we aim to provide a more comprehensive understanding of the clinical features of a novel homozygous TRAPPC9 mutation. In addition to ID, the siblings in this report suffered from ASD and specific stereotypes as hand-flapping behavior. Conclusion: Although there are inconsistencies in the presentation of ASD in TRAPPC9 mutations, repetitive behaviors (hand-flapping) were typical in our cases and several previous reports. The current mutation was described to cause a homozygous premature termination codon that resulted in the absence of the TRAPPC9 protein. We suggest that TRAPPC9 mutations are not only related to ID but also to ASD and hand-flapping behaviors.

Phenotypic and Brain Imaging Findings Associated With a 10p Proximal Deletion Including the WAC Gene: Case Report and Literature Review.

Microarray-based techniques are an important testing method in etiological studies of intellectual disability and autism spectrum disorder. Interstitial deletion in the p11-p12 region of chromosome 10 is rare, having been reported in just 12 cases to date. Intellectual disability associated with the WAC gene in this region is referred to as DeSanto-Shinawi syndrome . Although all individuals with p11-p12 region of chromosome 10 deletion share a common phenotype involving intellectual disability and dysmorphic features, individuals with DeSanto-Shinawi syndrome usually do not experience the cardiac and neurologic abnormalities or cryptorchidism associated with a 10p11-p12 deletion. With this case report, we aim to expand the phenotypic spectrum of 10p11-p12 deletion. Our patient was a 9-year-old boy with intellectual disability, autism symptoms, dysmorphic features, and behavioral abnormalities. He had no cardiac problems or neurologic symptoms such as hypotonia, feeding difficulties, or seizures. However, he presented cryptorchidism in addition to symptoms that are consistent with DeSanto-Shinawi syndrome. Array comparative genomic hybridization of genomic DNA isolated from a peripheral blood sample revealed a heterozygous deletion in 10p11.23-p12.1, which contains the WAC gene. We discuss our case in the context of a literature review of candidate genes. It is still difficult to establish genotype-phenotype correlations for neurologic, cardiac, and visual symptoms, and cryptorchidism, in individuals with a 10p11-p12 deletion. As more individuals are diagnosed with deletion in this chromosomal region, the associated phenotypes will become clearer.

Investigation of possible associations of the BDNF, SNAP-25 and SYN III genes with the neurocognitive measures: BDNF and SNAP-25 genes might be involved in attention domain, SYN III gene in executive function.

OBJECTIVES: Attention-deficit/hyperactivity disorder (ADHD) is a heterogeneous disorder and Sluggish Cognitive Tempo (SCT) might be a second inattention disorder that might be even affected by different attention pathways. SCT is characterized by daydreaming, mental confusion, staring blankly and hypoactivity. In the present study, we evaluated 5 common variants (rs6265, rs3746544, rs1051312, rs133946 and rs133945) located in 3 candidate genes (BDNF, SNAP25 and SYN III) that are known to take part in synaptic plasticity and neurotransmitter transmission. METHODS: We tested the effects of these variants on neuropsychological findings assessed by a computer-based neuropsychological test battery in children with inattention symptoms (SCT and/or ADHD). RESULTS: BDNF (rs6265), SNAP25 (rs3746544 and rs1051312) and SYN III (rs133946 and rs133945) polymorphisms were associated with variable cognitive measures. BDNF gene (rs6265) polymorphism Met allele carriers and SNAP25 gene (rs3746544) T allele carriers had an association with the attention domain. SNAP25 gene (rs1051312) C allele carriers were only associated with reaction time scores. Cognitive flexibility, which is one of the key components of executive function evaluation and shifting attention test scores were associated with BDNF (rs6265) Met allele and SYN III (rs133946) gene G allele. SYN III (rs133945) gene C allele carriers had an association with verbal memory correct hit scores. CONCLUSIONS: As a conclusion, BDNF, SNAP25 and SYN III genes were associated with specific neurocognitive outcomes in children with inattention symptoms. It is important to note that exploring genotyping effects on neurocognitive functions instead of a heterogeneous psychiatric diagnosis can improve our understanding of psychopathologies.

Autosomal Recessive Primary Microcephaly (MCPH) and Novel Pathogenic Variants in ASPM and WDR62 Genes.

Introduction: Autosomal recessive primary microcephaly (MCPH) is a disorder characterized by congenital microcephaly and intellectual disability without extra-central nervous system malformation. MCPH is a disease with heterogeneity in genotype and phenotype. For this reason, it is important to determine the genetic causes and genotype-phenotype relationship in MCPH, which causes lifelong impairment. In this study, we aimed to evaluate the clinical, genetic, and brain imaging findings of cases diagnosed with MCPH. Methods: Electroencephalogram and brain magnetic resonance imaging were performed for all cases. We evaluated genetic results of the 39 families including cases with suspected MCPH diagnosis. Results: Genetic diagnosis related to MCPH was provided in 11/39 (28.2%) of these families including 13/41 cases (31.7%). Variants of the WDR62 gene were the most common (61.5%) cause, and variants of the ASPM gene were the second most common cause (38.5%). We have found 6 novel variants and 4 previously reported variants in ASPM and WDR62 genes. Main brain imaging findings in our cases were lissencephaly, polymicrogyria, schizencephaly, pachygyria, and cortical dysplasia. Genetic counseling in 2 families whose genetic diagnosis was determined prevented them from having another child with MCPH. Discussion/Conclusion: Detection and reporting of novel variants is an important step in eliminating this disorder by providing families with appropriate genetic counseling.

Effect of Impairment on the Prevalence and Comorbidities of Attention Deficit Hyperactivity Disorder in a National Survey: Nation-Wide Prevalence and Comorbidities of ADHD.

OBJECTIVE: This study aimed to determine the prevalence and comorbidities of attention-deficit hyperactivity disorder (ADHD) by evaluating a large-scale nation-wide sample of children. METHOD: The inclusion criterion was being enrolled as a 2nd, 3rd, or 4th-grade student. A semi-structured diagnostic interview (K-SADS-PL), DSM-IV-Based Screening Scale for Disruptive Behavior Disorders, and assessment of impairment (by both parents and teachers) were applied to 5,842 participants. RESULTS: The prevalence of ADHD was 19.5% without impairment and 12.4% with impairment. Both ADHD with and without impairment groups had similar psychiatric comorbidity rates except for oppositional defiant disorder (ODD) and conduct disorder (CD) diagnoses. Impairment in the ADHD group resulted in significantly higher ODD and CD diagnoses. CONCLUSION: Even when impairment is not described, other psychiatric disorders accompany the diagnosis of ADHD and may cause impairment in the future. Impairment in the diagnosis of ADHD significantly increases the likelihood of ODD and CD.

The Role of Copy Number Variations and FHIT Gene on Phenotypic Characteristics of Cases Diagnosed with Autism Spectrum Disorder.

Copy number variations (CNVs) have been implied in the etiology of autism spectrum disorder (ASD), and microarray-based techniques are performed as a first-step genetic test. Our aim was to present clinical features and CNV profiles of patients with ASD and their parents. Array-CGH was applied to detect CNVs. Previously as likely pathogenic reported duplications were detected at 16p13.11 and 11p15.2p15.1. Other variants were found in 16p11.2p11.1, 3p14.2, 15q11.2, 10q11.22, 3p26.3, 4q13.3, 22q13.32q13.33, and 1q44 and were classified as variants of unknown significance. Deletion of the FHIT gene was associated with the regression of language and social skills without mental impairment. Paternal inheritance of difficulty in social skills and the FHIT gene was documented. In addition, varying olfactory receptor family genes were implicated in de novo and hereditary CNVs. In this study, we aimed to present the clinical characteristics of the cases and parents in more detail, especially in pathogenic CNV cases, which enables us to increase our knowledge on inherited CNVs and genotype-phenotype correlation. We suggest that both genetic and psychiatric evaluation of the parents of the cases is important for better understanding the clinical relevance of the CNV results.

Effects of the dopamine transporter gene on neuroimaging findings in different attention deficit hyperactivity disorder presentations.

Attention-Deficit/Hyperactivity Disorder (ADHD) is a phenotipically and neurobiologically heterogeneous disorder. Deficiencies at different levels in response inhibition, differences in dopamine transporter genotype (DAT1) and various symptomatic presentations contribute to ADHD heterogeneity. Integrating these three aspects into a functional neuroimaging research could help unreval specific neurobiological components of more phenotipically homogeneous groups of patients with ADHD. During the Go-NoGo trial, we investigated the effect of the DAT1 gene using 3 T MRI in 72 ADHD cases and 24 (TD) controls that typically developed between the ages 8 and 15 years. In the total ADHD group, DAT1 predicted homozygosity for the 10R allele and hypoactivation in the anterior cingulate cortex and paracingulate cortex. There were no significant activation differences between DAT1 10R/10R homozygotes and 9R carriers in TD controls. Subjects with predominantly inattentive ADHD (ADHD-I) presentation with DAT1 10R/10R homozygous reduced neuronal activation during Go trial particularly in the frontal regions and insular cortex, and in the parietal regions during NoGo trial (brain regions reported as part of Default Mode Network- DMN). Additionally, DAT1 10R/10R homozygousness was associated with increased occipital zone activation during only the Go trial in the ADHD combined presentation (ADHD-C) group. Our results point the three main findings: 1) The DAT1 gene is 10R homozygous for differentiated brain activation in ADHD cases but not in the TD controls, supporting the DAT1 gene as a potential marker for ADHD, 2) The relationship between the DAT1 gene and the occipital regions in ADHD-C group which may reflect compensatory mechanisms, 3) The relationship between DAT1 gene and the reduced DMN suppression for 9R carriers probabaly stems from the ADHD-I group.

DRD4 genotyping may differentiate symptoms of attention-deficit/hyperactivity disorder and sluggish cognitive tempo

Objective: Studies to reduce the heterogeneity of attention-deficit/hyperactivity disorder (ADHD) have increased interest in the concept of sluggish cognitive tempo (SCT). The aim of this study was to investigate if the prevalence of two variable-number tandem repeats (VNTRs) located within the 3′-untranslated region of the DAT1 gene and in exon 3 of the dopamine D4 receptor (DRD4) gene differ among four groups (31 subjects with SCT but no ADHD, 146 individuals with ADHD but no SCT, 67 subjects with SCT + ADHD, and 92 healthy controls). Methods: We compared the sociodemographic profiles, neurocognitive domains, and prevalence of two VNTRs in SCT and ADHD subjects versus typically developing (TD) controls. Results: The SCT without ADHD group had a higher proportion of females and lower parental educational attainment. Subjects in this group performed worse on neuropsychological tests, except for psychomotor speed and commission errors, compared to controls. However, the ADHD without SCT group performed significantly worse on all neuropsychological domains than controls. We found that 4R homozygosity for the DRD4 gene was most prevalent in the ADHD without SCT group. The SCT without ADHD group had the highest 7R allele frequency, differing significantly from the ADHD without SCT group. Conclusion: The 7R allele of DRD4 gene was found to be significantly more prevalent in SCT cases than in ADHD cases. No substantial neuropsychological differences were found between SCT and ADHD subjects.

Case report: diagnosis and treatment of attention deficit hyperactivity disorder and autism spectrum disorder in patients diagnosed with oculocutaneous albinism.

Oculocutaneous albinism (OCA) is a group of autosomal recessive disorders characterized by impairment in the melanin synthesis. We report two siblings with OCA who presented with symptoms of autism spectrum disorder and attention deficit hyperactivity disorder (ADHD). Ocular side effects occured after methylphenidate (MPH) treatment in the patient with ADHD and OCA. The diagnosis of OCA has been associated with difficulties in academic and social fields due to decreased visual activity and differentiation of phenotypic characteristics. Delayed diagnosis of comorbid neuropsychiatric disorders and MPH therapy may increase these difficulties. Patients with OCA require careful evaluation and treatment for neuropsychiatric disorders.

Diffusion tensor imaging findings in children with sluggish cognitive tempo comorbid Attention Deficit Hyperactivity Disorder.

Objective: The construct of Sluggish Cognitive Tempo (SCT) is characterized by daydreaming, mental confusion, staring blankly and hypoactivity. Our main goal was to explore neuropsychological differences in Attention Deficit Hyperactivity Disorder-Inattentive presentation (ADHD-IA) groups with and without SCT symptoms compared to healthy controls. After detecting specific neuropsychological differences, we examined white matter microstructure using Diffusion Tensor Imaging (DTI) data obtained from 3.0 Tesla MRI scans of the cases with SCT symptoms comparing to Typically Developing (TD) controls.Method: In this study, we included 24 cases in the ADHD-IA group with SCT symptoms, 57 cases in the ADHD-IA group without SCT symptoms and, 24 children in the TD group. We applied tract-based spatial statistics to the DTI measures for obtaining fractional anisotropy (FA), axial, radial and mean diffusivity (AD, RD, MD) to explore white matter differences for the whole brain.Results: Omission error scores and longer reaction time scores were specifically associated with inattention symptoms. Commission error scores were significantly and specifically related to SCT symptoms. Cases with SCT symptoms presented increased FA in the bilateral anterior and posterior limb of the internal capsule, bilateral cerebral peduncle, and the fornix than TD group.Conclusions: Neurobiological differences in ADHD cases are still relatively unexplored. We suggest that including an assessment for SCT in the neuropsychological and neuroimaging studies of ADHD may provide more consistent results.

DRD4 genotyping may differentiate symptoms of attention-deficit/hyperactivity disorder and sluggish cognitive tempo.

OBJECTIVE: Studies to reduce the heterogeneity of attention-deficit/hyperactivity disorder (ADHD) have increased interest in the concept of sluggish cognitive tempo (SCT). The aim of this study was to investigate if the prevalence of two variable-number tandem repeats (VNTRs) located within the 3'-untranslated region of the DAT1 gene and in exon 3 of the dopamine D4 receptor (DRD4) gene differ among four groups (31 subjects with SCT but no ADHD, 146 individuals with ADHD but no SCT, 67 subjects with SCT + ADHD, and 92 healthy controls). METHODS: We compared the sociodemographic profiles, neurocognitive domains, and prevalence of two VNTRs in SCT and ADHD subjects versus typically developing (TD) controls. RESULTS: The SCT without ADHD group had a higher proportion of females and lower parental educational attainment. Subjects in this group performed worse on neuropsychological tests, except for psychomotor speed and commission errors, compared to controls. However, the ADHD without SCT group performed significantly worse on all neuropsychological domains than controls. We found that 4R homozygosity for the DRD4 gene was most prevalent in the ADHD without SCT group. The SCT without ADHD group had the highest 7R allele frequency, differing significantly from the ADHD without SCT group. CONCLUSION: The 7R allele of DRD4 gene was found to be significantly more prevalent in SCT cases than in ADHD cases. No substantial neuropsychological differences were found between SCT and ADHD subjects.

Comparisons between sluggish cognitive tempo and ADHD-restrictive inattentive presentation phenotypes in a clinical ADHD sample.

There is a debate how different ADHD cases with a comorbid sluggish cognitive tempo (SCT) phenotype are from subjects with a pure inattentive ADHD presentation (ADHD-restrictive inattentive presentation). In this study, 214 patients aged 8-15 years from an ADHD outpatient clinic were assessed, and 100 typically developing controls (TD) were recruited as comparisons. No psychiatric comorbidities except for oppositional defiant disorder were allowed. We compared 29 cases with ADHD + SCT with 34 ADHD-RI cases and 92 TD subjects on sociodemographic profiles, CBCL subscales scores and neurocognitive findings. Regarding sociodemographic profiles (age, gender and parental education) and CBCL subscales, ADHD + SCT and ADHD-RI cases did not differ in any score (all p > 0.05). Comparing with SCT cases, ADHD-RI cases presented slower psychomotor speed and worse neurocognitive index (p < 0.001). We found that only SCT was independently associated with a lower performance in total memory score. ADHD-RI was independently associated with longer reaction time. Our findings suggest that although SCT might be expected to present longer reaction time, we found that slower psychomotor speed and longer reaction time scores were related to inattention. Overall, SCT and ADHD-RI groups were distinguished by differential associations with measures of memory and reaction time.

Validity of proposed DSM-5 ADHD impulsivity symptoms in children.

The American Psychiatric Association (APA) working group on Attention-Deficit/Hyperactivity Disorder (ADHD) proposed the inclusion of four new impulsivity symptoms. However, they were not included in DSM-5 due to the lack of sufficient evidence. The aim of this study is to investigate the performance of the proposed four ADHD impulsivity symptoms with respect to: (a) ADHD factor structure; (b) performance in predicting clinical impairment; (c) specificity for ADHD diagnosis and (d) best symptomatic threshold to predict clinical impairment. The sample comprised 416 children (31 ADHD subjects according to both DSM-IV and proposed DSM-5, 20 ADHD subjects according to just one diagnostic system and 365 controls) from 12 schools. Diagnoses were derived using semi-structured interviews and ADHD rating scales. Results from confirmatory factor analysis indicate that addition of the four new impulsivity items provided a slightly better factor structure if compared to models including only 18 items. Regression analyses showed that only one of the new impulsivity symptoms (impatient) was part of the list of best predictors of impairment. None of the four new impulsivity items was specifically associated with ADHD diagnosis. The best cutoff point in the hyperactivity/impulsivity dimension for predicting impairment did not change significantly. Overall, our findings suggest that the determination on how to best capture impulsivity dimension as part of the ADHD construct needs more investigation and that there is not enough evidence to include these four assessed impulsivity symptoms as part of the ADHD criteria.