Alternative titles; symbols
HGNC Approved Gene Symbol: SDCCAG8
Cytogenetic location: 1q43-q44 Genomic coordinates (GRCh38): 1:243,256,041-243,500,091 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 1q43-q44 | Bardet-Biedl syndrome 16 | 615993 | Autosomal recessive | 3 |
| Senior-Loken syndrome 7 | 613615 | Autosomal recessive | 3 |
Kenedy et al. (2003) cloned an SDCCAG8 cDNA, which they called CCCAP (centrosomal colon cancer autoantigen protein), from a human placenta cDNA library. By sequence analysis they discovered that a fragment of CCCAP had been identified as colon cancer autoantigen NY-CO-8 by Scanlan et al. (1998). Kenedy et al. (2003) found at least 3 alternatively spliced CCCAP transcripts, including a full-length transcript encoding a deduced 713-amino acid protein with a molecular mass of 82.5 kD. Kenedy et al. (2003) cloned the mouse CCCAP cDNA from a spleen cDNA library. The human and mouse proteins share 71% identity and have the same predicted secondary structure consisting of a predicted N-terminal globular domain and a C-terminal coiled-coil domain. Human and mouse CCCAP transcripts were found to be ubiquitously expressed but at very low copy number (Kenedy et al., 2003). Endogenous mouse BALB/c 3T3 fibroblasts and ectopic human CCCAP in U2-osteosarcoma cells localized to centrosomes during interphase and mitosis.
Otto et al. (2010) determined that the SDCCAG8 gene comprises 18 exons.
Kenedy et al. (2003) stated that the CCCAP gene maps to chromosome 1q43-q44.
Based on the centrosomal localization of human and mouse CCCAP and the ability of mouse CCCAP to homo-oligomerize, Kenedy et al. (2003) suggested that CCCAP is a stable centrosomal component with a structural role in the centrosomal architecture or the microtubule organizing activities of the centrosome matrix.
In a mammalian renal epithelial cell line, Otto et al. (2010) found that Sdccag8 localizes to centrosomes, but at a distance from centrioles and from distal centrosomal appendages. There was colocalization with ninein (608684), a marker of centrosomal appendages, and with NPHP5 (609237) and OFD1 (300170). Sdccag8 also localized to cell-cell junctions. Further cellular studies led Otto et al. (2010) to conclude that SDCCAG8 is located at the distal ends of both centrioles and that it colocalizes to centrosomes throughout the cell cycle. Human SDCCAG8 was also found in human retinal pigment epithelial cells, where it localized in the vicinity of centrosomes. Yeast 2-hybrid screening studies showed that SDCCAG8 interacts directly with OFD1, and studies in mouse photoreceptor cells showed that Sdccag8 colocalized with Nphp5 in the transition zone.
Chaki et al. (2012) found that NPHP10 colocalized with the DNA damage response proteins TIP60 (KAT5; 601409), SC35 (SRSF2; 600813), CEP164 (614848), and ZNF423 (604557) at nuclear foci in immortalized human retinal pigment epithelial cells. This noncentrosomal localization of NPHP10 suggested a role for this protein in DNA damage repair. Chaki et al. (2012) suggested that defects in DNA repair may play a role in nephronophthisis-related ciliopathies, such as Senior-Loken syndrome (SLSN7; 613615).
Otto et al. (2010) screened patients with what they called 'nephronophthisis-related ciliopathies' (NPHP-RC), disorders that affect the kidney, retina, brain, and liver with prenatal-onset dysplasia or childhood-onset tissue degeneration, for mutations in candidate genes using homozygosity mapping combined with exome capture. They identified 12 different truncating mutations in SDCCAG8 in 10 families. All affected individuals from these 10 families had nephronophthisis and retinal degeneration. Otto et al. (2010) identified a homozygous truncating mutation in the SDCCAG8 gene (613524.0001) in 2 sibs with Senior-Loken syndrome-7 (SLSN7; 613615), who were born of consanguineous parents from Reunion Island. They found homozygous mutations in SDCCAG8 in 5 other families with a phenotype consistent with Senior-Loken syndrome. Recessive SDCCAG8 mutations accounted for 3.3% (6 of 182) cases from a worldwide SLSN cohort. Affected individuals from 4 of the 10 families had been diagnosed with Bardet-Biedl syndrome (see 209900). In 2 of these families, which were consanguineous, affected individuals carried homozygous mutations in SDCCAG8 (e.g., 613524.0004, 613524.0005); the other 2 families were nonconsanguineous, and compound heterozygous SDCCAG8 mutations were present in affected members (e.g., 613524.0006, 613524.0007). Otto et al. (2010) described the phenotypes of SDCCAG8 mutation carriers as 'SLSN with some additional BBS-related features'; no patient diagnosed with BBS had polydactyly.
In 2 sibs of East Indian descent with Bardet-Biedl syndrome (BBS16; 615993), Billingsley et al. (2012) identified compound heterozygous truncating mutations in the SDCCAG8 gene (613524.0006, 613524.0007). The patients had obesity, early-onset end-stage renal failure requiring transplant in late childhood, short stature, mild cognitive impairment, and evidence of retinal dystrophy with relatively preserved vision. Polydactyly was not present. Functional studies of the variants were not performed. These same compound heterozygous mutations had been found by Otto et al. (2010) in an Indian patient with features of BBS, including NPHP, end-stage kidney failure, retinal dystrophy, obesity, and mild mental retardation.
In a 15-year-old girl, born of nonconsanguineous parents, with SLSN7, Tay and Vincent (2020) identified compound heterozygous mutations in the SDCCAG8 gene, a splice site mutation (613524.0004) and a 1-bp duplication (613524.0008). The mutations, which were found by next-generation sequencing, segregated with the disorder in the family.
Otto et al. (2010) demonstrated that knockout of the Sdccag8 gene in zebrafish resulted in multiple developmental defects, including abnormal body axis curvature, shortened and broadened tails, kidney cysts at 72 hours post fertilization, and hydrocephalus. Knockdown of murine Sdccag8 in renal epithelial cells resulted in the formation of spheroids with architectural defects characterized by disturbed localization of beta-catenin (CTNNB1; 116806) at the basolateral membrane, fewer tight junctions, and an irregular lumen. These findings were consistent with a defect in cell polarity and lumen formation, which may reflect the renal tubular defects found in individuals with a congenital SDCCAG8 mutation. Increased intracellular cAMP caused a dose-dependent loss of Sdccag8 from cell-cell junctions compared to controls.
In 2 sibs with Senior-Loken syndrome-7 (SLSN7; 613615), born of consanguineous parents from Reunion Island, Otto et al. (2010) identified a homozygous 1-bp deletion (1420delG) in exon 12 of the SDCCAG8 gene, resulting in frameshift and premature termination (Glu474fsTer493). The mutation was found by homozygosity mapping followed by exon capture and massively parallel sequencing. One patient had onset of nephronophthisis at age 4 years and retinal degeneration at age 14 years, whereas the other was blind by age 7 years and had onset of renal disease at age 14 years. The mutation was not found in 270 control individuals.
In 2 affected members of a consanguineous Algerian family with Senior-Loken syndrome-7 (SLSN7; 613615), Otto et al. (2010) identified a homozygous 1-bp insertion (1339insG) in exon 11 of the SDCCAG8 gene, resulting in frameshift and premature termination (Glu447fsTer463). Onset of nephronophthisis occurred at ages 7 and 4 years, respectively, and flat electroretinograms were observed at ages 13 and 6 years, respectively. One of the patients had mild mental retardation. The mutation was not found in 270 control individuals.
By direct exon sequencing of 118 families with Senior-Loken syndrome, Otto et al. (2010) found a homozygous truncating mutation in the SDCCAG8 gene in 1 family, consistent with Senior-Loken syndrome-7 (SLSN7; 613615). The mutation was a 4-bp deletion (1946delGTGT) in exon 16, resulting in frameshift and premature termination (Cys649fsTer658). The patient had retinal degeneration, and nephronophthisis was confirmed by renal biopsy at age 22 years. The mutation was not found in 270 control individuals.
Bardet-Biedl Syndrome 16
In 4 affected members of a consanguineous Gypsy family with Bardet-Biedl syndrome (BBS16; 615993), Otto et al. (2010) identified a homozygous deep intronic mutation (c.740+356C-T) in intron 7 of the SDCCAG8 gene, predicted to cause loss of an exonic splice enhancer site, with the result of aberrant splicing introducing an in-frame stop codon. RT-PCR and immunoblotting studies showed almost complete absence of the full-length product. All patients had nephronophthisis (NPHP) and retinal degeneration as well as mild mental retardation and obesity, although none had polydactyly. One of the patients had relatively late onset of renal and retinal disease in the twenties, which may have been due to some residual protein function. The mutation was not found in 270 control individuals. Schaefer et al. (2010) noted that this family, with 5 affected members in 2 sibships, had been recruited initially because of the acute manifestation of chronic renal failure coupled to a variety of respiratory defects.
Senior-Loken Syndrome 7
In a 15-year-old girl with Senior-Loken syndrome-7 (SLSN7; 613615), Tay and Vincent (2020) identified compound heterozygous mutations in the SDCCAG8 gene: c.740+356C-T and a novel 1-bp duplication (c.1324dupC; 613524.0008) leading to a frameshift and premature termination (Gln442ProfsTer22). The mutations were found by next-generation sequencing. The parents were determined to be carriers.
In 2 affected members of a consanguineous family with Bardet-Biedl syndrome (BBS16; 615993), Otto et al. (2010) identified a homozygous 679A-T transversion in exon 7 of the SDCCAG8 gene, resulting in a lys227-to-ter (K227X) substitution. Both individuals had NPHP and retinal degeneration, as well as some mild mental retardation, obesity, and hypogenitalism, although neither had polydactyly. The mutation was not found in 270 control individuals. Schaefer et al. (2010) noted that this family was French.
In an Indian patient with features of Bardet-Biedl syndrome, including end-stage renal failure, retinal dystrophy, obesity, and mild mental retardation (BBS16; 615993), Otto et al. (2010) identified compound heterozygosity for mutations in the SDCCAG8 gene: a 1-bp deletion (c.1444delA) in exon 12, resulting in a frameshift and premature termination (Thr482fsTer493), and a 4-bp deletion (c.1627_1630delGATA; 613524.0007) in exon 14, resulting in a frameshift and premature termination (Asp543fsTer566). Otto et al. (2010) did not find either mutation in over 1,270 control chromosomes. Polydactyly was not present in this patient.
In 2 sibs of East Indian descent with BBS, Billingsley et al. (2012) identified the same compound heterozygous truncating mutations in the SDCCAG8 gene that had been identified by Otto et al. (2010). Billingsley et al. (2012) referred to the changes observed at the protein level as Thr482LysfsTer12 and Asp543AlsfsTer24. The mutations segregated with the disorder in the family and were not found in 69 matched control individuals. The patients had obesity, early-onset end-stage renal failure requiring transplant in late childhood, short stature, and mild cognitive impairment. One patient had nonalcoholic fatty liver disease. Visual acuity and central fields were preserved in the teenage years in both patients. The optical coherence tomography showed preservation of the retinal lamination at the fovea; fundus autofluorescence demonstrated a perifoveal ring of hyperfluorescence consistent with retinitis pigmentosa. Full-field ERG showed rod function to be more severely affected than cone function in both cases. Polydactyly was not present. Functional studies of the variants were not performed.
For discussion of the 4-bp deletion in the SDCCAG8 gene (c.1627_1630delGATA) that was found in compound heterozygous state in patients with Bardet-Biedl syndrome-16 (BBS16; 615993) by Otto et al. (2010) and Billingsley et al. (2012), see 613524.0006.
For discussion of the 1-bp duplication (c.1324dupC) in the SDCCAG8 gene, leading to a frameshift and premature termination (Gln442ProfsTer22), that was found in compound heterozygous state in a girl with Senior-Loken syndrome-7 (SLSN7; 613615) by Tay and Vincent (2020), see 613524.0004.
Billingsley, G., Vincent, A., Deveault, C., Heon, E. Mutational analysis of SDCCAG8 in Bardet-Biedl syndrome patients with renal involvement and absent polydactyly. Ophthalmic Genet. 33: 150-154, 2012. [PubMed: 22626039] [Full Text: https://doi.org/10.3109/13816810.2012.689411]
Chaki, M., Airik, R., Ghosh, A. K., Giles, R. H., Chen, R., Slaats, G. G., Wang, H., Hurd, T. W., Zhou, W., Cluckey, A., Gee, H. Y., Ramaswami, G., and 61 others. Exome capture reveals ZNF423 and CEP164 mutations, linking renal ciliopathies to DNA damage response signaling. Cell 150: 533-548, 2012. [PubMed: 22863007] [Full Text: https://doi.org/10.1016/j.cell.2012.06.028]
Kenedy, A. A., Cohen, K. J., Loveys, D. A., Kato, g. J., Dang, C. V. Identification and characterization of the novel centrosome-associated protein CCCAP. Gene 303: 35-46, 2003. [PubMed: 12559564] [Full Text: https://doi.org/10.1016/s0378-1119(02)01141-1]
Otto, E. A., Hurd, T. W., Airik, R., Chaki, M., Zhou, W., Stoetzel, C., Patil, S. B., Levy, S., Ghosh, A. K., Murga-Zamalloa, C. A., van Reeuwijk, J., Letteboer, S. J. F., and 43 others. Candidate exome capture identifies mutation of SDCCAG8 as the cause of a retinal-renal ciliopathy. Nature Genet. 42: 840-850, 2010. [PubMed: 20835237] [Full Text: https://doi.org/10.1038/ng.662]
Scanlan, M. J., Chen, Y.-T., Williamson, B., Gure, A. O., Stockert, E., Gordan, J. D., Tureci, O., Sahin, U., Pfreundschuh, M., Old, L. J. Characterization of human colon cancer antigens recognized by autologous antibodies. Int. J. Cancer 76: 652-658, 1998. [PubMed: 9610721] [Full Text: https://doi.org/10.1002/(sici)1097-0215(19980529)76:5<652::aid-ijc7>3.0.co;2-p]
Schaefer, E., Zaloszyc, A., Lauer, J., Durand, M., Stutzmann, F., Perdomo-Trujillo, Y., Redin, C., Greene, V. B., Toutain, A., Perrin, L., Gerard, M., Caillard, S., and 12 others. Mutations in SDCCAG8/NPHP10 cause Bardet-Biedl syndrome and are associated with penetrant renal disease and absent polydactyly. Molec. Syndromol. 1: 273-281, 2010. [PubMed: 22190896] [Full Text: https://doi.org/10.1159/000331268]
Tay, S. A., Vincent, A. L. Senior-Loken syndrome and intracranial hypertension. Ophthalmic Genet. 41: 354-357, 2020. [PubMed: 32432520] [Full Text: https://doi.org/10.1080/13816810.2020.1766086]