ClinVar Genomic variation as it relates to human health

The allele frequency of the c.377+6_377+9del variant in MECP2 (NM_004992.3) is 0.014% in the East Asian sub population in gnomAD, which is high enough to meet the BS1 criteria based on thresholds defined by the ClinGen Rett/Angelman-like Expert Panel for Rett/AS-like conditions (BS1). The c.377+6_377+9del variant is found in a patient with an alternate molecular basis of disease (internal database - GeneDx) (BP5). In summary, the c.377+6_377+9del variant in MECP2 is classified as Likely Benign based on the ACMG/AMP criteria (BS1, BP5).

The MECP2 c.377+6_377+9delTAAG variant (rs267608459), also known as IVS2+2delTAAG, has not been reported in individuals with Rett syndrome but has been observed in an individual with infantile autism (Lam 2000). This variant is also reported in ClinVar (Variation ID: 156059). This variant is found in the East Asian population with an allele frequency of 0.01% (2/13,856 alleles) in the Genome Aggregation Database. This is an intronic variant, and computational analyses (Alamut v.2.11) predict that this variant may impact splicing by weaking the nearby canonical donor splice site. However, given the lack of clinical and functional data, the significance of the c.377+6_377+9delTAAG variant is uncertain at this time. References: Lam CW et al. Spectrum of mutations in the MECP2 gene in patients with infantile autism and Rett syndrome. J Med Genet. 2000 Dec;37(12):E41. PMID: 11106359.

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.

This sequence change falls in intron 3 of the MECP2 gene. It does not directly change the encoded amino acid sequence of the MECP2 protein. It affects a nucleotide within the consensus splice site. This variant is present in population databases (rs267608459, gnomAD 0.02%), including at least one homozygous and/or hemizygous individual. This variant has been observed in individual(s) with autism (PMID: 11106359). This variant is also known as IVS+2delTAAG. ClinVar contains an entry for this variant (Variation ID: 156059). 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 may create or strengthen a splice site. 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.

This variant has been collected from RettBASE and curated to current modified ACMG/AMP criteria. Based on the classification scheme defined by the ClinGen Rett/Angelman-like Expert Panel for Rett/AS-like Disorders Specifications to the ACMG/AMP Variant Interpretation Guidelines VCEP 3.0, this variant is classified as likely benign. At least the following criteria are met: The allele frequency of this variant in at least one population in gnomAD is between 0.008% and 0.03% (BS1).

Variant summary: MECP2 c.377+6_377+9delTAAG alters a nucleotide located close to a canonical splice site and therefore could affect mRNA splicing, leading to a significantly altered protein sequence. Several computational tools predict a significant impact on normal splicing: Four predict the variant abolishes a canonical 5' splicing donor site. Two predict the variant creates a cryptic 5' donor site. However, these predictions have yet to be confirmed by functional studies. The variant allele was found at a frequency of 5.9e-06 in 1195715 control chromosomes. The available data on variant occurrences in the general population are insufficient to allow any conclusion about variant significance. c.377+6_377+9delTAAG has been reported in the literature in at-least one individual affected with infantile autism (example: Lam_2000). These report(s) do not provide unequivocal conclusions about association of the variant with Rett Syndrome. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. The following publication has been ascertained in the context of this evaluation (PMID: 11106359). ClinVar contains an entry for this variant (Variation ID: 156059). Based on the evidence outlined above, the variant was classified as uncertain significance.