chr15-72686228-A-G

Position:

• chr15-72686228-A-G

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.1A>G​(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 0.00000212 in 1,412,324 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: 0.0000021 (0 hom.)
• Consequence: BBS4 NM_033028.5 start_lost
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:3
• Conservation: PhyloP100: 3.15

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 445809
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 15-72686228-A-G is Pathogenic according to our data. Variant chr15-72686228-A-G is described in ClinVar as [Likely_pathogenic]. Clinvar id is 886465.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.1A>G	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.1A>G	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: 0.0000113 AC: 2 AN: 176590 Hom.: 0 AF XY: 0.0000106 AC XY: 1 AN XY: 93936

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.0000371

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: 0.000210

GnomAD4 exome AF: 0.00000212 AC: 3 AN: 1412324 Hom.: 0 Cov.: 31 AF XY: 0.00000287 AC XY: 2 AN XY: 697916

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.0000265

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 9.20e-7

Gnomad4 OTH exome AF: 0.0000171

GnomAD4 genome Cov.: 32

Bravo AF: 0.00000756

ExAC AF: 0.00000851 AC: 1

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:3

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Bardet-Biedl syndrome Pathogenic:2

Pathogenic, criteria provided, single submitter	clinical testing	Labcorp Genetics (formerly Invitae), Labcorp	Dec 22, 2023	This sequence change affects the initiator methionine of the BBS4 mRNA. The next in-frame methionine is located at codon 173. 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 variant has not been reported in the literature in individuals affected with BBS4-related conditions. ClinVar contains an entry for this variant (Variation ID: 886465). 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. For these reasons, this variant has been classified as Pathogenic. -
Likely pathogenic, criteria provided, single submitter	clinical testing	Women's Health and Genetics/Laboratory Corporation of America, LabCorp	Feb 15, 2023	Variant summary: BBS4 c.1A>G (p.Met1Val) alters the initiation codon and is predicted to result either in absence of the protein or truncation of the encoded protein due to translation initiation at a downstream codon. An alternative downstream in-frame start codon (p.Met173) is located in exon 8 of the encoded protein. Two of two in-silico tools predict a benign effect of the variant on protein function. The variant allele was found at a frequency of 1.1e-05 in 176590 control chromosomes (gnomAD). The available data on variant occurrences in the general population are insufficient to allow any conclusion about variant significance. c.1A>G has been reported in the literature in an individual reportedly affected with Bardet-Biedl Syndrome with a non-informative genotype (example: Hou_ 2020). These report(s) do not provide unequivocal conclusions about association of the variant with Bardet-Biedl Syndrome. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. Deletion of exon 4 (internally classified pathogenic) and deletion of exons 3-4 have been classified pathogenic in ClinVar (CV ID: 657391). Two clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar after 2014 and classified the variant as VUS and pathogenic. Based on the evidence outlined above, the variant was classified as likely pathogenic. -

BBS4-related disorder Pathogenic:1

Likely pathogenic, no assertion criteria provided

clinical testing

PreventionGenetics, part of Exact Sciences

Sep 13, 2024

The BBS4 c.1A>G variant is predicted to disrupt the translation initiation site (Start Loss). This variant was reported in a large cohort study integrating whole genome sequencing with deep phenotyping in adult participants (Table S1 in Hou et al 2020. PubMed ID: 31980526). This variant is reported in 0.0037% of alleles in individuals of Latino descent in gnomAD. This variant is interpreted as likely pathogenic. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.27	D
BayesDel_noAF	Pathogenic	0.15
CADD	Benign	19
DANN	Benign	0.95
DEOGEN2	Benign	0.21	T
Eigen	Benign	-0.36
Eigen_PC	Benign	-0.31
FATHMM_MKL	Benign	0.62	D
LIST_S2	Uncertain	0.90	D
M_CAP	Pathogenic	0.70	D
MetaRNN	Pathogenic	0.98	D
MetaSVM	Benign	-0.80	T
MutationTaster	Benign	1.0	D;D;D
PROVEAN	Benign	-0.87	N
REVEL	Uncertain	0.35
Sift	Benign	0.12	T
Sift4G	Uncertain	0.058	T
Polyphen		0.0070	B
Vest4		0.81
MutPred		0.99		Loss of MoRF binding (P = 0.1006);
MVP		0.69
ClinPred		0.97	D
GERP RS		2.5
Varity_R		0.43
gMVP		0.36

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: rs773109542; hg19: chr15-72978569;