Bi-allelic Mutations in FAM149B1 Cause Abnormal Primary Cilium and a Range of Ciliopathy Phenotypes in Humans

Am J Hum Genet. 2019 Apr 4;104(4):731-737. doi: 10.1016/j.ajhg.2019.02.018.

Ranad Shaheen ¹, Nan Jiang ², Fatema Alzahrani ¹, Nour Ewida ¹, Tarfa Al-Sheddi ¹, Eman Alobeid ¹, Damir Musaev ², Valentina Stanley ², Mais Hashem ¹, Niema Ibrahim ¹, Firdous Abdulwahab ¹, Abduljabbar Alshenqiti ³, Fatma Mujgan Sonmez ⁴, Nadia Saqati ³, Hamad Alzaidan ³, Mohammad M Al-Qattan ⁵, Futwan Al-Mohanna ⁶, Joseph G Gleeson ², Fowzan S Alkuraya ⁷

Affiliations

1 Department of Genetics, King Faisal Specialist Hospital and Research Center, PO Box 3354, Riyadh 11211, Saudi Arabia.
2 Laboratory for Pediatric Brain Disease, Howard Hughes Medical Institute, Department of Neurosciences, University of California, San Diego, La Jolla, CA 92093, USA.
3 Department of Medical Genetics, King Faisal Specialist Hospital and Research Center, Riyadh 1211, Saudi Arabia.
4 Karadeniz Technical University, Faculty of Medicine, Department of Child Neurology, Retired Lecturer, Trabzon 61080, Turkey.
5 Department of Surgery, King Saudi University, Riyadh 11451, Saudi Arabia.
6 Department of Cell Biology, King Faisal Specialist Hospital and Research Center, PO Box 245, Riyadh 11211, Saudi Arabia.
7 Department of Genetics, King Faisal Specialist Hospital and Research Center, PO Box 3354, Riyadh 11211, Saudi Arabia; Saudi Human Genome Program, King Abdulaziz City for Science and Technology, Riyadh 12371, Saudi Arabia; Department of Anatomy and Cell Biology, College of Medicine, Alfaisal University, Riyadh 11533, Saudi Arabia. Electronic address: falkuraya@kfshrc.edu.sa.

PMID: 30905400 DOI: 10.1016/j.ajhg.2019.02.018

Abstract

Ciliopathies are clinical disorders of the primary cilium with widely recognized phenotypic and genetic heterogeneity. In two Arab consanguineous families, we mapped a ciliopathy phenotype that most closely matches Joubert syndrome (hypotonia, developmental delay, typical facies, oculomotor apraxia, polydactyly, and subtle posterior fossa abnormalities) to a single locus in which a founder homozygous truncating variant in FAM149B1 was identified by exome Sequencing. We subsequently identified a third Arab consanguineous multiplex family in which the phenotype of Joubert syndrome/oral-facial-digital syndrome (OFD VI) was found to co-segregate with the same founder variant in FAM149B1. Independently, autozygosity mapping and exome Sequencing in a consanguineous Turkish family with Joubert syndrome highlighted a different homozygous truncating variant in the same gene. FAM149B1 encodes a protein of unknown function. Mutant fibroblasts were found to have normal ciliogenesis potential. However, distinct cilia-related abnormalities were observed in these cells: abnormal accumulation IFT complex at the distal tips of the cilia, which assumed bulbous appearance, increased length of the primary cilium, and dysregulated SHH signaling. We conclude that FAM149B1 is required for normal ciliary biology and that its deficiency results in a range of ciliopathy phenotypes in humans along the spectrum of Joubert syndrome.

Keywords

Joubert syndrome; SHH; bulbous ciliary tip; ciliary length; oral-facial-digital syndrome.

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