chr3-121799376-T-G

Variant names:

• chr3-121799376-T-G
• NM_001023570.4:c.588-2A>C

Variant summary

Our verdict is Uncertain significance. The variant received 4 ACMG points: 4P and 0B. PVS1_Moderate PM2

The NM_001023570.4(IQCB1):​c.588-2A>C variant causes a splice acceptor, intron change. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a pathogenic outcome for this variant. 3/3 splice prediction tools predicting alterations to normal splicing. No clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar.

• Frequency: Genomes: not found (cov: 32)
• Consequence: IQCB1 NM_001023570.4 splice_acceptor, intron
• Scores: Splicing: ADA: 1.000
• Clinical Significance: Not reported in ClinVar
• Conservation: PhyloP100: 4.63
• Publications: 0 publications found

Genes affected

IQCB1 (HGNC:28949): (IQ motif containing B1) This gene encodes a nephrocystin protein that interacts with calmodulin and the retinitis pigmentosa GTPase regulator protein. The encoded protein has a central coiled-coil region and two calmodulin-binding IQ domains. It is localized to the primary cilia of renal epithelial cells and connecting cilia of photoreceptor cells. The protein is thought to play a role in ciliary function. Defects in this gene result in Senior-Loken syndrome type 5. Alternative splicing results in multiple transcript variants. A pseudogene of this gene is found on chromosome 6. [provided by RefSeq, Jan 2016]

IQCB1 Gene-Disease associations (from GenCC):

• ciliopathy

  Inheritance: AR Classification: DEFINITIVE Submitted by: ClinGen
• Senior-Loken syndrome 5

  Inheritance: AR Classification: DEFINITIVE, STRONG Submitted by: Labcorp Genetics (formerly Invitae), Ambry Genetics
• Leber congenital amaurosis

  Inheritance: AD Classification: SUPPORTIVE Submitted by: Orphanet
• Senior-Loken syndrome

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet

ACMG classification

Our verdict: Uncertain_significance. The variant received 4 ACMG points.

• PVS1: Splicing +-2 bp (donor or acceptor) variant, product NOT destroyed by NMD, known LOF gene, truncates exone, which is 0.09961046 fraction of the gene. Cryptic splice site detected, with MaxEntScore 3.4, offset of 15, new splice context is: attcgtggtgatttactcAGaat. Cryptic site results in inframe change. If cryptic site found is not functional and variant results in exon loss, it results in frameshift change.
• PM2: Very rare variant in population databases, with high coverage

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_001023570.4. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Sel.	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	IQCB1	NM_001023570.4	MANE Select	c.588-2A>C		splice_acceptor intron	N/A	NP_001018864.2	Q15051-1
	IQCB1	NM_001319107.2		c.588-2A>C		splice_acceptor intron	N/A	NP_001306036.1	Q15051-1
	IQCB1	NM_001023571.4		c.587+7968A>C		intron	N/A	NP_001018865.2	Q15051-2

Ensembl Transcripts

Sel.	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	IQCB1	ENST00000310864.11	TSL:1 MANE Select	c.588-2A>C		splice_acceptor intron	N/A	ENSP00000311505.6	Q15051-1
	IQCB1	ENST00000349820.10	TSL:1	c.587+7968A>C		intron	N/A	ENSP00000323756.7	Q15051-2
	IQCB1	ENST00000923631.1		c.660-2A>C		splice_acceptor intron	N/A	ENSP00000593690.1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome Cov.: 24

GnomAD4 genome Cov.: 32

ClinVar

Not reported in ClinVar

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.62	D
BayesDel_noAF	Benign	-0.090
CADD	Pathogenic	34
DANN	Benign	0.96
Eigen	Pathogenic	0.85
Eigen_PC	Uncertain	0.64
FATHMM_MKL	Uncertain	0.87	D
PhyloP100		4.6
Mutation Taster		=13/87	disease causing

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	1.0
dbscSNV1_RF	Pathogenic	0.74
SpliceAI score (max)		0.68		Details are displayed if max score is > 0.2
DS_AG_spliceai		0.66		Position offset: -17
DS_AL_spliceai		0.68		Position offset: -2

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

MaxEntScan Visualizer can be used to analyze the impact of this mutation on the neighboring sequence.

Other links and lift over

hg19: chr3-121518223;