Muhammad Ismail Khan1, Muhammad Latif2, Maria Saif3, Hilal Ahmad3, Atta Ullah Khan4, Muhammad Imran Naseer5,6, Hafiz Muhammad Jafar Hussain7, Musharraf Jelani3. 1. Department of Zoology, Islamia College Peshawar, Peshawar, Khyber Pakhtunkhwa, Pakistan. 2. Centre for Genetics and Inherited Diseases (CGID), Taibah University, Al-Madinah, Al-Munawwarah, Saudi Arabia. 3. Centre for Omic Sciences, Islamia College Peshawar, Peshawar, Khyber Pakhtunkhwa, Pakistan. 4. Department of Medicine, Pak International Medical College Phase 5, Hayatabad Peshawar, Khyber Pakhtunkhwa, Pakistan. 5. Center of Excellence in Genomic Medicine Research, King Abdulaziz University, Jeddah, Saudi Arabia. 6. Department of Medical Laboratory Technology, Faculty of Applied Medical Sciences, King Abdulaziz University, Jeddah, Saudi Arabia. 7. Institute of Nephrology, Ruijin Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China.
Abstract
BACKGROUND: Joubert syndrome (JBTS) is a heterogenous disorder characterized by intellectual disability, developmental delays, molar tooth sign in brain imaging, hypotonia, ocular motor apraxia and overlapping features of ciliopathies. There are 36 clinical subtypes of JBTS, with an equal number of genes known so far for this phenotype. METHODS: Whole exome sequencing (WES) and Sanger sequencing were performed for the molecular diagnosis of a Pakhtun family affected with Joubert syndrome type 9 (JBTS9). RESULTS: A novel homozygous missense variant (c.4417C>G; Pro1473Ala) in exon 34 was identified in coiled-coil and C2 domains-containing the protein 2A (CC2D2A; NM_001080522) gene. The variant co-segregated in autosomal recessive fashion within the family and was not found in 200 ethnically matched unaffected individuals. In silico analyses supported the pathogenic effect of the altered CC2D2A protein. CONCLUSIONS: To the best of our knowledge, this is the first report of CC2D2A alteration co-segragating with a JBTS9 phenotype in a Pakhtun family from Pakistan. Our findings broaden the pathogenic spectrum of JBTS9, adding a novel variant to CC2D2A variation pool. WES analysis is a successful molecular diagnostic tool for rare genetic disorders, especially in those populations where the marriage of cousins is more frequent. Efficient and accurate genetic testing and counselling of the affected families are helpful for patient management and for reducing the disease burden in future generations.
BACKGROUND: Joubert syndrome (JBTS) is a heterogenous disorder characterized by intellectual disability, developmental delays, molar tooth sign in brain imaging, hypotonia, ocular motor apraxia and overlapping features of ciliopathies. There are 36 clinical subtypes of JBTS, with an equal number of genes known so far for this phenotype. METHODS: Whole exome sequencing (WES) and Sanger sequencing were performed for the molecular diagnosis of a Pakhtun family affected with Joubert syndrome type 9 (JBTS9). RESULTS: A novel homozygous missense variant (c.4417C>G; Pro1473Ala) in exon 34 was identified in coiled-coil and C2 domains-containing the protein 2A (CC2D2A; NM_001080522) gene. The variant co-segregated in autosomal recessive fashion within the family and was not found in 200 ethnically matched unaffected individuals. In silico analyses supported the pathogenic effect of the altered CC2D2A protein. CONCLUSIONS: To the best of our knowledge, this is the first report of CC2D2A alteration co-segragating with a JBTS9 phenotype in a Pakhtun family from Pakistan. Our findings broaden the pathogenic spectrum of JBTS9, adding a novel variant to CC2D2A variation pool. WES analysis is a successful molecular diagnostic tool for rare genetic disorders, especially in those populations where the marriage of cousins is more frequent. Efficient and accurate genetic testing and counselling of the affected families are helpful for patient management and for reducing the disease burden in future generations.