chr15-72686229-T-C

Position:

• chr15-72686229-T-C

Variant summary

Our verdict is Pathogenic. Variant got 20 ACMG points: 20P and 0B. PVS1 PS1_Moderate PM2 PP5_Very_Strong

The NM_033028.5(BBS4):​c.2T>C​(p.Met1?) variant causes a start lost change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000566 in 1,412,618 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Likely pathogenic (★★).

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000057 (0 hom.)
• Consequence: BBS4 NM_033028.5 start_lost
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:2
• Conservation: PhyloP100: 2.70

Genes affected

BBS4 (HGNC:969): (Bardet-Biedl syndrome 4) This gene is a member of the Bardet-Biedl syndrome (BBS) gene family. Bardet-Biedl syndrome is an autosomal recessive disorder characterized by severe pigmentary retinopathy, obesity, polydactyly, renal malformation and cognitive disability. The proteins encoded by BBS gene family members are structurally diverse. The similar phenotypes exhibited by mutations in BBS gene family members are likely due to the protein's shared roles in cilia formation and function. Many BBS proteins localize to the basal bodies, ciliary axonemes, and pericentriolar regions of cells. BBS proteins may also be involved in intracellular trafficking via microtubule-related transport. The protein encoded by this gene has sequence similarity to O-linked N-acetylglucosamine (O-GlcNAc) transferases in plants and archaebacteria and in human forms a multi-protein "BBSome" complex with seven other BBS proteins. Alternate splicing results in multiple transcript variants. [provided by RefSeq, Mar 2016]

HIGD2B (HGNC:26984): (HIG1 hypoxia inducible domain family member 2B) Predicted to be involved in mitochondrial respirasome assembly. Predicted to be integral component of membrane. Predicted to be active in mitochondrion. [provided by Alliance of Genome Resources, Apr 2022]

ACMG classification

Verdict is Pathogenic. Variant got 20 ACMG points.

• PVS1: Start lost variant, no new inframe start found.
• PS1: Another start lost variant in NM_033028.5 (BBS4) was described as [Likely_pathogenic] in ClinVar as 886465
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 15-72686229-T-C is Pathogenic according to our data. Variant chr15-72686229-T-C is described in ClinVar as [Likely_pathogenic]. Clinvar id is 445809.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
BBS4	NM_033028.5	c.2T>C	p.Met1?	start_lost	1/16	ENST00000268057.9
HIGD2B	NM_001350932.3			upstream_gene_variant		ENST00000311755.6

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
BBS4	ENST00000268057.9	c.2T>C	p.Met1?	start_lost	1/16	1	NM_033028.5	P1
HIGD2B	ENST00000311755.6			upstream_gene_variant		1	NM_001350932.3	P1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD3 exomes AF: 0.00000565 AC: 1 AN: 177122 Hom.: 0 AF XY: 0.00 AC XY: 0 AN XY: 94232

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.0000370

Gnomad ASJ exome AF: 0.00

Gnomad EAS exome AF: 0.00

Gnomad SAS exome AF: 0.00

Gnomad FIN exome AF: 0.00

Gnomad NFE exome AF: 0.00

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.00000566 AC: 8 AN: 1412618 Hom.: 0 Cov.: 31 AF XY: 0.00000573 AC XY: 4 AN XY: 698122

Gnomad4 AFR exome AF: 0.0000309

Gnomad4 AMR exome AF: 0.0000264

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.0000125

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.00000368

Gnomad4 OTH exome AF: 0.0000171

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:2

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Center for Pediatric Genomic Medicine, Children's Mercy Hospital and Clinics

Aug 31, 2017

- -

Bardet-Biedl syndrome Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

Invitae

Aug 17, 2023

For these reasons, this variant has been classified as Pathogenic. This variant disrupts a region of the BBS4 protein in which other variant(s) (Deletion (Exons 3-4)) have been determined to be pathogenic (PMID: 11381270). This suggests that this is a clinically significant region of the protein, and that variants that disrupt it are likely to be disease-causing. ClinVar contains an entry for this variant (Variation ID: 445809). This variant has not been reported in the literature in individuals affected with BBS4-related conditions. The frequency data for this variant in the population databases is considered unreliable, as metrics indicate poor data quality at this position in the gnomAD database. This sequence change affects the initiator methionine of the BBS4 mRNA. The next in-frame methionine is located at codon 173. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.27	D
BayesDel_noAF	Pathogenic	0.14
CADD	Benign	20
DANN	Benign	0.97
DEOGEN2	Benign	0.23	T
Eigen	Benign	-0.21
Eigen_PC	Benign	-0.15
FATHMM_MKL	Benign	0.60	D
LIST_S2	Uncertain	0.90	D
M_CAP	Pathogenic	0.92	D
MetaRNN	Pathogenic	0.99	D
MetaSVM	Benign	-0.67	T
MutationTaster	Benign	1.0	D;D;D
PROVEAN	Benign	-0.84	N
REVEL	Uncertain	0.35
Sift	Uncertain	0.011	D
Sift4G	Uncertain	0.013	D
Polyphen		0.067	B
Vest4		0.78
MutPred		0.99		Gain of helix (P = 0.0199);
MVP		0.81
ClinPred		0.98	D
GERP RS		3.7
Varity_R		0.79
gMVP		0.40

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.0		Details are displayed if max score is > 0.2

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

Publications

LitVar

Other links and lift over

dbSNP: rs1302879683; hg19: chr15-72978570;