ClinVar Genomic variation as it relates to human health

The NM_00138 c.3509G>A, is a missense variant in FBN1 predicted to cause a substitution of an arginine acid by histidine at amino acid 1170 (p.Arg1170His). This variant has been previously reported in several apparently unrelated individuals with Marfan syndrome (PMID 26787436, internal data), incomplete Marfan syndrome, including with skeletal features and/or mitral valve prolapse (PMID 7870075, 9837823, 17418587, 17627385, 17657824), in individuals with isolated thoracic aortic aneurysm and/or dissection (internal data) and in other phenotypes like arterial dissection and venous bleeding (internal data). This variant was found to segregate with disease in seven affected individuals with incomplete Marfan syndrome from three families (PMID 7870075, 9837823, internal data). This variant has been found to co-occur with different pathogenic variants in FBN1 (BP2), TGFBR1, and TGFRB2 (BP5) (internal data). This variant has been identified in 286 individuals of European non-Finnish origin (MAF: 0.2%) (BA1; https://gnomad.broadinstitute.org/, version 2.1.1). The variant in FBN1 has been reported 21 times in ClinVar: 16 times as likely benign and 5 times as uncertain significance (Variation ID: 16451). Computational prediction tools and conservation analysis are unclear on the predicted impact on the protein (REVEL: 0.502). Functional studies, including in-vitro splicing analysis, found that this variant had no impact on splicing (PMID 21895641, 32123317). The constraint z-score for missense variants affecting FBN1 is 5.06, however due to the presence of benign arguments, PP2 cannot be used. In summary, this variant meets criteria to be classified as benign for Marfan syndrome based on the ACMG/AMP criteria applied, as specified by the ClinGen FBN1 VCEP: BA1, BP2, BP5.

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.

p.Arg1170His in exon 28 of FBN1: This variant is not expected to have clinical s ignificance because it has been identified in 0.2% (124/66684) of European chrom osomes by the Exome Aggregation Consortium (ExAC, http://exac.broadinstitute.org ; dbSNP rs137854475). Arginine (Arg) at position 1170 is not conserved in evolut ionarily distant species and at least 10 birds, reptiles, and fish carry a histi dine (His) at this position, supporting that this change may be tolerated. This variant has been identified by our laboratory in 6 individuals with features of Marfan syndrome; however, two of these individuals were compound heterozygotes f or a pathogenic variant sufficient to explain their disease. Although this varia nt has been reported in individuals with features of Marfan syndrome in the lite rature, this variant is likely benign based on its frequency in the general popu lation, lack of conservation, and the presence of other variants to explain dise ase in multiple individuals.

This variant was observed as part of a predisposition screen in an ostensibly healthy population. A literature search was performed for the gene, cDNA change, and amino acid change (where applicable). No publications were found based on this search. Allele frequency data from public databases allowed determination this variant is unlikely to cause disease. Therefore, this variant is classified as likely benign.

This variant was observed as part of a predisposition screen in an ostensibly healthy population. A literature search was performed for the gene, cDNA change, and amino acid change (where applicable). No publications were found based on this search. Allele frequency data from public databases allowed determination this variant is unlikely to cause disease. Therefore, this variant is classified as likely benign.

This variant was observed as part of a predisposition screen in an ostensibly healthy population. A literature search was performed for the gene, cDNA change, and amino acid change (where applicable). No publications were found based on this search. Allele frequency data from public databases allowed determination this variant is unlikely to cause disease. Therefore, this variant is classified as likely benign.

This variant was observed as part of a predisposition screen in an ostensibly healthy population. A literature search was performed for the gene, cDNA change, and amino acid change (where applicable). No publications were found based on this search. Allele frequency data from public databases allowed determination this variant is unlikely to cause disease. Therefore, this variant is classified as likely benign.

This variant was observed as part of a predisposition screen in an ostensibly healthy population. A literature search was performed for the gene, cDNA change, and amino acid change (where applicable). No publications were found based on this search. Allele frequency data from public databases allowed determination this variant is unlikely to cause disease. Therefore, this variant is classified as likely benign.

This variant was observed as part of a predisposition screen in an ostensibly healthy population. A literature search was performed for the gene, cDNA change, and amino acid change (where applicable). No publications were found based on this search. Allele frequency data from public databases allowed determination this variant is unlikely to cause disease. Therefore, this variant is classified as likely benign.

This variant was observed as part of a predisposition screen in an ostensibly healthy population. A literature search was performed for the gene, cDNA change, and amino acid change (where applicable). No publications were found based on this search. Allele frequency data from public databases allowed determination this variant is unlikely to cause disease. Therefore, this variant is classified as likely benign.

Variant summary: FBN1 c.3509G>A (p.Arg1170His) results in a non-conservative amino acid change located in one of the EGF-like calcium-binding domains (IPR001881) of the encoded protein sequence. Three of five in-silico tools predict a benign effect of the variant on protein function. The variant allele was found at a frequency of 0.0014 in 396164 control chromosomes in the gnomAD database (version 2.1 and 3.1 datasets), including 1 homozygote. The observed variant frequency is approximately 12-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 benign. c.3509G>A has been reported in the literature in cohorts of individuals affected with Marfan Syndrome or Marfan-like syndrome (e.g. Hayward_1994, Montgomery_1998, Comeglio_2007, Robinson_2011, Howarth_2007, Waldmuller_2007, Volk_2014, Franken_2016), however, in some of these studies an incomplete Marfan phenotype was noted, or no exact phenotype information was provided. In a recent case-control study the variant was found in 11 cases of imaging supported nonsyndromic aortopathy and/or mitral valve disease, and in 14 carriers without cardiovascular disease, whereas only 12/101 (12%) of controls without pathogenic FBN1 variants (with sufficient imaging), had evidence of mitral valve or aortic disease in this study (Damrauer_2019). Co-occurrences with other pathogenic variants have been reported (FBN1 c.4913delA, p.Tyr1638fsX2 and FBN1 c.1633C>T, p.Arg545Cys, in internal LCA samples), providing supporting evidence for a benign role. Two publications reported that the variant had no effect on splicing examining blood RNA samples (Robinson_2011, Wai_2020), however these data do not allow any conclusion for the protein level effect of the variant. 15 other submitters have provided clinical-significance assessments for this variant in ClinVar after 2014 mostly without evidence for independent evaluation, and classified the variant as VUS (n=5), or likely benign (n=10). Based on the evidence outlined above, though the variant could be associated with an increased risk for nonsyndromic aortopathy and/or mitral valve disease, it was classified for the Marfan Syndrome phenotype as likely benign.

FBN1 NM_000138.4 exon 29 p.Arg1170His (c.3509G>A): This variant has been reported in at least four individuals with incomplete/suspected Marfan syndrome, segregating with suspected features in at least two different families (Hayward 1994 PMID:7870075, Montgomery 1998 PMID:9837823, Comeglio 2007 PMID:17657824, Stavropoulos 2016 PMID:28567303). Of note, these reported probands presented with primarily skeletal abnormalities; none fully met Ghent criteria for Marfan syndrome. Additionally, this variant did not segregate with disease in one family with suspected Marfan syndrome that was tested in our lab. This variant is present in 0.2% (286/129170) of European alleles in the Genome Aggregation Database (http://gnomad.broadinstitute.org/variant/15-48779352-C-T) and is present in ClinVar, with several labs classifying this variant as likely benign (Variation ID:16451). This variant amino acid Histidine (His) is present in several bird species and is not well conserved among evolutionarily distant species; this suggests that this variant may not impact the protein. Additional computational prediction tools do not suggest an impact. In summary, data on this variant is insufficient for disease classification. Therefore, the clinical significance of this variant is uncertain.

This alteration is classified as likely benign based on a combination of the following: seen in unaffected individuals, population frequency, intact protein function, lack of segregation with disease, co-occurrence, RNA analysis, in silico models, amino acid conservation, lack of disease association in case-control studies, and/or the mechanism of disease or impacted region is inconsistent with a known cause of pathogenicity.

FBN1: BS1

This variant is classified as likely benign based on ACMG/AMP sequence variant interpretation guidelines (Richards et al. 2015 PMID: 25741868, with internal and published modifications).

Variant interpretted as Likely benign and reported on 07/24/2018 by GTR ID 26957. GenomeConnect assertions are reported exactly as they appear on the patient-provided report from the testing laboratory. GenomeConnect staff make no attempt to reinterpret the clinical significance of the variant.