Identification of a Novel Variant in CC2D1A Gene Linked to Autosomal Recessive Intellectual Disability 3 in an Iranian Family and Investigating the Structure and Pleiotropic Effects of this Gene

Zahra Rashvand; Hossein Najmabadi; Kimia Kahrizi; Hossein Mozhdehipanah; Mohammad Moradi; Zohreh Estaki; Khadijeh Taherkhani; Nooshin Nikzat; Reza Najafipour; Mir Davood Omrani

doi:10.22037/ijcn.v18i1.42188

Identification of a Novel Variant in CC2D1A Gene Linked to Autosomal Recessive Intellectual Disability 3 in an Iranian Family and Investigating the Structure and Pleiotropic Effects of this Gene

Iran J Child Neurol. 2024 Winter;18(1):25-41. doi: 10.22037/ijcn.v18i1.42188. Epub 2024 Jan 18.

Authors

Affiliations

¹ Department of Medical Genetics, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
² Genetics Research Center, the University of Social Welfare and Rehabilitation Sciences, Tehran, Iran.
³ Depatment of Neurology Boali Hospital, Qazvin University of Medical Sciences, Qazvin, Iran.
⁴ Cellular and Molecular Research Centre, Qazvin University of Medical Sciences, Qazvin, Iran.
⁵ Department of Pediatric Dentistry, School of Dentistry, Qazvin University of Medical Sciences, Qazvin, Iran.
⁶ Urogenital Stem Cell Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.

Abstract

Objectives: Intellectual disability (ID) represents a significant health challenge due to its diverse and intricate nature. A multitude of genes play a role in brain development and function, with defects in these genes potentially leading to ID. Considering that many of these genes have yet to be identified, and those identified have only been found in a small number of patients, no complete description of the phenotype created by these genes is available. CC2D1A is one of the genes whose loss-of-function mutation leads to a rare form of non-syndromic ID-3(OMIM*610055), and four pathogenic variants have been reported in this gene so far.

Materials & methods: n the current study, two affected females were included with an initial diagnosis of ID who were from an Iranian family with consanguineous marriage. Whole-exome sequencing was used to identify the probable genetic defects. The Genotypic and phenotypic characteristics of the patients were compared with a mutation in the CC2D1A gene, and then the structure of the gene and its reported variants were investigated.

Results: The patients carried a novel homozygous splicing variant (NM_017721, c.1641+1G>A) in intron 14, which is pathogenic according to the ACMG guideline. Loss-of-function mutations in CC2D1A have severe phenotypic consequences such as ID, autism spectrum disorder (ASD), and seizures. However, missense mutations lead to ASD with or without ID, and in some patients, they cause ciliopathy.

Conclusion: This study reports the fifth novel, probably pathogenic variant in the CC2D1A gene. Comparing the clinical and molecular genetic features of the patients with loss-of-function mutation helped to describe the phenotype caused by this gene more precisely. Investigating the CC2D1A gene's mutations and structure revealed that it performs multiple functions. The DM14 domain appears more pivotal in triggering severe clinical symptoms, including ID, than the C2 domain.

Keywords: CC2D1A; Intellectual disability; Iran; Mutation; Whole-exome sequencing.