Mutations in CKAP2L, the Human Homolog of the Mouse Radmis Gene, Cause Filippi Syndrome

Abstract

Filippi syndrome is a rare, presumably autosomal-recessive disorder characterized by microcephaly, pre- and postnatal growth failure, syndactyly, and distinctive facial features, including a broad nasal bridge and underdeveloped alae nasi. Some affected individuals have intellectual disability, seizures, undescended testicles in males, and teeth and hair abnormalities. We performed homozygosity mapping and whole-exome sequencing in a Sardinian family with two affected children and identified a homozygous frameshift mutation, c.571dupA (p.Ile191Asnfs(∗)6), in CKAP2L, encoding the protein cytoskeleton-associated protein 2-like (CKAP2L). The function of this protein was unknown until it was rediscovered in mice as Radmis (radial fiber and mitotic spindle) and shown to play a pivotal role in cell division of neural progenitors. Sanger sequencing of CKAP2L in a further eight unrelated individuals with clinical features consistent with Filippi syndrome revealed biallelic mutations in four subjects. In contrast to wild-type lymphoblastoid cell lines (LCLs), dividing LCLs established from the individuals homozygous for the c.571dupA mutation did not show CKAP2L at the spindle poles. Furthermore, in cells from the affected individuals, we observed an increase in the number of disorganized spindle microtubules owing to multipolar configurations and defects in chromosome segregation. The observed cellular phenotypes are in keeping with data from in vitro and in vivo knockdown studies performed in human cells and mice, respectively. Our findings show that loss-of-function mutations in CKAP2L are a major cause of Filippi syndrome.

Induced Pluripotent Stem Cell-Derived Mesenchymal Stromal Cells Are Functionally and Genetically Different From Bone Marrow-Derived Mesenchymal Stromal Cells

“…Mesengenesis of iPSCs by inhibiting TGF‐β/Activin/Nodal signaling with SB‐431542 resulted in a greater expression of VEGFR1 ( FLT1 ), a marker of vascular endothelial cells in iMSCs than in BM‐MSCs . Mesengenic induction using FGF2 and PDGF followed by cell sorting for a CD105 + CD24 − population also gave rise to a heterogeneous culture with greater expression of vascular endothelial markers ( CL‐P1 and FAM43A ) and neuroprogenitor markers ( EFNB3 , SLITRK5 , and CKAP2L ) in ESC‐MSCs than in BM‐MSCs . Moreover, irrespective of the derivation methods used, extremely low expression of MSC‐associated genes was often detected in these PSC‐MSCs, including IL6 , BST1 , SFRP4 , and VCAM1 .…”

Mosaic CREBBP mutation causes overlapping clinical features of Rubinstein–Taybi and Filippi syndromes

“…5 Variants in this gene were excluded in our patient. Sanger sequencing in three families with a clinical diagnosis of FLPIS that were tested negative for variants in CKAP2L yielded no variants in C9orf173.…”

“…characteristic features include bilateral syndactyly of fingers and toes, microcephaly, ID with weak speech, short stature, bilateral cryptorchidism, and a characteristic face with prominent nasal bridge and bulging forehead. 2,5 The syndrome has a variable phenotype, 2 including seizures, visual disturbances, and ectodermal abnormalities (Table 1). 2,5 Skeletal abnormalities have been reported on X-rays, including retarded bone age, brachymesophalangism (particularly of the fifth finger), hypoplasia of the radial heads with complete dislocation of the elbows, and bilateral synostosis of the carpal bones.…”

“…Recently, CKAP2L was identified as the FLPIS gene. 5 As no disease-causing variants in CREBBP, EP300, and CKAP2L were identified by Sanger sequencing on DNA isolated from blood, we performed a WES analysis. We identified an autosomal recessive deletion in C9orf173 that was absent from multiple large databases at the time of analysis.…”

“…Initial molecular diagnostic analysis, however, revealed no abnormalities in the RTS genes, CREBBP 3 and EB300, 4 nor in the FLPIS gene, CKAP2L. 5 With whole-exome sequencing (WES) analysis, we identified a novel autosomal recessive deletion in C9orf173 that was novel at the time of analysis, causing a frameshift. However, no other FLPIS cases harbored variants in this gene.…”