IntroductionAutism spectrum disorder (ASD) is a highly heterogeneous neurodevelopmental disorder with many contributing risk genes. Multiple intellectual disability (ID) susceptibility genes have been identified in ASDs to date. The trafficking protein particle complex subunit 9 TRAPPC9 (OMIM#611966) in an autosomal recessive intellectual disability (ID) gene associated with not fully penetrant phenotype combining secondary microcephaly, dysmorphic facial features, obesity, autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD).ObjectivesThe aim of this study is to consider TRAPPC9 deficiency in autosomal recessive ID with ASD.MethodsWe present the observation of two siblings, born to Tunisian consanguineous and healthy parents, followed up for syndromic intellectual disability (ID) associated ASD and microcephaly. A clinical exome sequencing was performed to one child using a Trusight One kit of Illumina. We used sanger sequencing to validate the suspected variant for the other child and to specify the parental segregation.ResultsA homozygous pathogenic variant in the TRAPPC9 (NM_001160372.4) gene, c.1414C > T (p. Arg472Ter) were identified in one child. Sanger sequencing confirmed the homozygosity profile of this variant for the other child while the parents were both heterozygous carriers.ConclusionsRepetitive behaviours, especially hand-flapping, were the mean ASD feature in our patients. The current variant is known in the Tunisian population. It is described to lead to the creation of a premature stop codon and a truncating protein causing a TRAPPC9 deficiency. The impairing neuronal NFkB signalling due to TRAPPC9 deficiency has been suggested to be implicated in ASD. Due to the profound ID seen in both patients, we suggest the classification of ASD related to TRAPPC9 deficiency as “secondary” rather than “primary”.Our results support the implication of TRAPPC9 in secondary ASD and shed the light on the possibility of screening p. Arg472Ter in Tunisian patients with this form of ASD as it is a recurrent mutation in the Tunisian population.Disclosure of InterestNone Declared