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The 16p11.2 duplication (BP4-BP5) is associated with Autism Spectrum Disorder (ASD), although significant heterogeneity exists. Quantitative ASD, behavioral and neuropsychological measures and DSM-IV diagnoses in child and adult carriers were compared with familial non-carrier controls, and to published results from deletion carriers. The 16p11.2 duplication phenotype ranges widely from asymptomatic presentation to significant disability. The most common diagnoses were intellectual disability, motor delays and Attention Deficit Hyperactivity Disorder in children, and anxiety in adults. ASD occurred in nearly 20 % of child cases, but a majority of carriers did not show the unique social features of ASD. The 16p11.2 duplication phenotype is characterized by wider variability than the reciprocal deletion, likely reflecting contributions from additional risk factors.

Background Deletion of the recurrent ~600 kb BP4-BP5 chromosomal region 16p11.2 has been associated with a wide range of neurodevelopmental outcomes. Methods To clarify the phenotype of 16p11.2 deletion, we examined the psychiatric and developmental presentation of predominantly clinically referred individuals, with a particular emphasis on broader autism phenotype characteristics in individuals with recurrent ~600 kb chromosome 16p11.2 deletions. Using an extensive standardized assessment battery across three clinical sites, 85 individuals with the 16p11.2 deletion and 153 familial control subjects were evaluated for symptom presentation and clinical diagnosis. Results Individuals with the 16p11.2 deletion presented with a high frequency of psychiatric and developmental disorders (>90%). The most commonly diagnosed conditions were developmental coordination disorder, phonologic processing disorder, expressive and receptive language disorders (71% of individuals >3 years old with a speech and language–related disorder), and autism spectrum disorder. Individuals with the 16p11.2 deletion not meeting diagnostic criteria for autism spectrum disorder had a significantly higher prevalence of autism-related characteristics compared with the familial noncarrier control group. Individuals with the 16p11.2 deletion had a range of intellectual ability, but IQ scores were 26 points lower than noncarrier family members on average. Conclusions Clinically referred individuals with the 16p11.2 deletion have high rates of psychiatric and developmental disorders and provide a genetically well-defined group to study the emergence of developmental difficulties, particularly associated with the broader autism phenotype.

In the overlap between the fields of neurology, psychiatry, and pediatrics, it may be hard to find a term with as much generality as neurodevelopmental disorders (NDD). Not surprisingly, these disorders have a number of different but possibly overlapping etiologies. New genome-wide discovery platforms, including chromosomal microarrays and whole-exome sequencing, have led to the discovery of many new genes and have pointed to the importance of de novo mutations functioning in an autosomal dominant fashion as key causes of this group of conditions, perhaps accounting for 50% of these patients. Animal models (particularly rodent) have made significant progress in understanding some of the biological mechanisms behind these disorders, but progress in the development of novel pharmacological interventions has been more challenging. These advances in genetics have also pointed to the importance of testing patient cohorts that are etiologically homogeneous to make progress in imaging and biomarker development. This convergence of tools and well-characterized patient cohorts will undoubtedly lead to rapid expansion in our understanding of NDD and suggests that real advances in disease-altering treatments may not be far off.

Joubert syndrome-related disorders (JSRDs) are autosomal recessive pleiotropic conditions sharing a peculiar cerebellar and brainstem malformation known as the 'molar tooth sign' (MTS). Recently, mutations in a novel ciliary gene, RPGRIP1L, have been shown to cause both JSRDs and Meckel-Gruber syndrome. We searched for RPGRIP1L mutations in 120 patients with proven MTS and phenotypes representative of all JSRD clinical subgroups. Two homozygous mutations, the previously reported p.T615P in exon 15 and the novel c.2268_2269delA in exon 16, were detected in 2 of 16 families with cerebello-renal presentation ( approximately 12%). Conversely, no pathogenic changes were found in patients with other JSRD phenotypes, suggesting that RPGRIP1L mutations are largely confined to the cerebello-renal subgroup, while they overall represent a rare cause of JSRD (

Author(s): Valente, E M; Brancat, F; Silhavy, J L; Castori, M; March, S E; Barrano, G; Bertini, E; Boltshauser, E; Zaki, M S; Abdel-Aleem, A; Abdel-Salam, GMH; Bellacchlo, E; Battini, R; Cruse, R P; Dobyns, W B; Krishnamoorthy, K S; Lagier-Tourenne, C; Magee, A; Pascual-Castroviejo, I; Salpietro, C D; Sarco, D; Dallapiccola, B; Gleeson, J G | Abstract: Joubert syndrome (JS) is a recessively inherited developmental brain disorder with several identified causative chromosomal loci. It is characterized by hypoplasia of the cerebellar vermis and a particular midbrain-hindbrain "molar tooth" sign, a finding shared by a group of Joubert syndrome-related disorders (JSRDs), with wide phenotypic variability. The frequency of mutations in the first positionally cloned gene, AHI1, is unknown. Methods: We searched for mutations in the AHI1 gene among a cohort of 137 families with JSRD and radiographically proven molar tooth sign. Results: We identified 15 deleterious mutations in 10 families with pure JS or JS plus retinal and/or additional central nervous system abnormalities. Mutations among families with JSRD including kidney or liver involvement were not detected. Transheterozygous mutations were identified in the majority of those without history of consanguinity. Most mutations were truncating or splicing errors, with only one missense mutation in the highly conserved WD40 repeat domain that led to disease of similar severity. Interpretation AHI1 mutations are a frequent cause of disease in patients with specific forms of JSRD.