rs747274959

Positions:

• chr15-48494257-G-A
• chr15-48494257-G-C

Variant summary

Our verdict is Benign. Variant got -7 ACMG points: 0P and 7B. BP4_Moderate BP6 BS2

The NM_000138.5(FBN1):​c.2678-3C>T variant causes a splice region, splice polypyrimidine tract, intron change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.0000171 in 1,459,672 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a benign outcome for this variant. 3/3 splice prediction tools predict no significant impact on normal splicing. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars).

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 0.000017 (0 hom.)
• Consequence: FBN1 NM_000138.5 splice_region, splice_polypyrimidine_tract, intron
• Scores: Splicing: ADA: 0.001115
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications U:2 B:3
• Conservation: PhyloP100: 1.35

Genes affected

FBN1 (HGNC:3603): (fibrillin 1) This gene encodes a member of the fibrillin family of proteins. The encoded preproprotein is proteolytically processed to generate two proteins including the extracellular matrix component fibrillin-1 and the protein hormone asprosin. Fibrillin-1 is an extracellular matrix glycoprotein that serves as a structural component of calcium-binding microfibrils. These microfibrils provide force-bearing structural support in elastic and nonelastic connective tissue throughout the body. Asprosin, secreted by white adipose tissue, has been shown to regulate glucose homeostasis. Mutations in this gene are associated with Marfan syndrome and the related MASS phenotype, as well as ectopia lentis syndrome, Weill-Marchesani syndrome, Shprintzen-Goldberg syndrome and neonatal progeroid syndrome. [provided by RefSeq, Apr 2016]

ACMG classification

Verdict is Benign. Variant got -7 ACMG points.

• BP4: Computational evidence support a benign effect (BayesDel_noAF=-0.44).
• BP6: Variant 15-48494257-G-A is Benign according to our data. Variant chr15-48494257-G-A is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 380618.We mark this variant Likely_benign, oryginal submissions are: {Uncertain_significance=2, Likely_benign=3}.
• BS2: High AC in GnomAdExome4 at 25 AD gene.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
FBN1	NM_000138.5	c.2678-3C>T		splice_region_variant, splice_polypyrimidine_tract_variant, intron_variant		ENST00000316623.10
FBN1	NM_001406716.1	c.2678-3C>T		splice_region_variant, splice_polypyrimidine_tract_variant, intron_variant

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
FBN1	ENST00000316623.10	c.2678-3C>T		splice_region_variant, splice_polypyrimidine_tract_variant, intron_variant		1	NM_000138.5	P1

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD3 exomes AF: 0.0000718 AC: 18 AN: 250742 Hom.: 0 AF XY: 0.0000664 AC XY: 9 AN XY: 135604

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.000492

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: 0.000163

GnomAD4 exome AF: 0.0000171 AC: 25 AN: 1459672 Hom.: 0 Cov.: 29 AF XY: 0.0000193 AC XY: 14 AN XY: 726332

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.000380

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: 0.00000720

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 33

Alfa AF: 0.0000712 Hom.: 0

Bravo AF: 0.0000189

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Uncertain:2 Benign:3

Revision: criteria provided, conflicting classifications

Submissions by phenotype

not specified Benign:2

Likely benign, criteria provided, single submitter	clinical testing	GeneDx	Sep 13, 2015	This variant is considered likely benign or benign based on one or more of the following criteria: it is a conservative change, it occurs at a poorly conserved position in the protein, it is predicted to be benign by multiple in silico algorithms, and/or has population frequency not consistent with disease. -
Likely benign, criteria provided, single submitter	clinical testing	Women's Health and Genetics/Laboratory Corporation of America, LabCorp	Nov 15, 2023	Variant summary: FBN1 c.2678-3C>T alters a non-conserved nucleotide located close to a canonical splice site and therefore could affect mRNA splicing, leading to a significantly altered protein sequence. Consensus agreement among computation tools predict no significant impact on normal splicing. However, these predictions have yet to be confirmed by functional studies. The variant allele was found at a frequency of 7.2e-05 in 250742 control chromosomes, predominantly at a frequency of 0.00049 within the Latino subpopulation in the gnomAD database. The observed variant frequency within Latino control individuals in the gnomAD database is approximately 4.36 fold of the estimated maximal expected allele frequency for a pathogenic variant in FBN1 causing Marfan Syndrome phenotype (0.00011), strongly suggesting that the variant is a benign polymorphism found primarily in populations of Latino origin. To our knowledge, no occurrence of c.2678-3C>T in individuals affected with Marfan Syndrome and no experimental evidence demonstrating its impact on protein function have been reported. Three submitters have cited clinical-significance assessments for this variant to ClinVar after 2014: one submitter classified the variant as likely benign while two classified as VUS. Based on the evidence outlined above, the variant was classified as likely benign. -

Marfan syndrome Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Center for Human Genetics, Inc, Center for Human Genetics, Inc

Nov 01, 2016

- -

Marfan syndrome;C4707243:Familial thoracic aortic aneurysm and aortic dissection Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Invitae

Dec 01, 2023

This sequence change falls in intron 22 of the FBN1 gene. It does not directly change the encoded amino acid sequence of the FBN1 protein. It affects a nucleotide within the consensus splice site. This variant is present in population databases (rs747274959, gnomAD 0.04%), and has an allele count higher than expected for a pathogenic variant. This variant has not been reported in the literature in individuals affected with FBN1-related conditions. ClinVar contains an entry for this variant (Variation ID: 380618). Variants that disrupt the consensus splice site are a relatively common cause of aberrant splicing (PMID: 17576681, 9536098). Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant is not likely to affect RNA splicing. In summary, the available evidence is currently insufficient to determine the role of this variant in disease. Therefore, it has been classified as a Variant of Uncertain Significance. -

Familial thoracic aortic aneurysm and aortic dissection Benign:1

Likely benign, criteria provided, single submitter

clinical testing

CHEO Genetics Diagnostic Laboratory, Children's Hospital of Eastern Ontario

Mar 10, 2023

- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_noAF	Benign	-0.44
CADD	Benign	13
DANN	Benign	0.64

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Benign	0.0011
dbscSNV1_RF	Benign	0.094
SpliceAI score (max)		0.010		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: rs747274959; hg19: chr15-48786454;