ClinVar Genomic variation as it relates to human health

This variant was determined to be of uncertain significance according to ACMG Guidelines, 2015 [PMID:25741868].

Variant identified in a patient with autism; however, it is unclear whether a second variant in this gene was identified (Saskin et al., 2017); In silico analysis supports that this missense variant does not alter protein structure/function; This variant is associated with the following publications: (PMID: 24813812, 29300326, 34168679, 31130284, 28250423)

Variant summary: DHCR7 c.376G>A (p.Val126Ile) results in a conservative amino acid change in the encoded protein sequence. Three of five in-silico tools predict a damaging effect of the variant on protein function. The variant allele was found at a frequency of 0.00012 in 250706 control chromosomes (gnomAD). This frequency is not significantly higher than estimated for a pathogenic variant in DHCR7 causing Smith-Lemli-Opitz Syndrome (0.00012 vs 0.0043), allowing no conclusion about variant significance. c.376G>A has been reported in the literature in a homozygous 12 months old dysmorphic male with microcephaly, and strabismus (example: Monies_2019). These data indicate that the variant may be associated with disease. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. The following publications have been ascertained in the context of this evaluation (PMID: 34168679, 24813812, 31130284, 28250423). Nine submitters have cited clinical-significance assessments for this variant to ClinVar after 2014. All submitters classified the variant as uncertain significance. Based on the evidence outlined above, the variant was classified as VUS-possibly pathogenic.

The c.376G>A (p.V126I) alteration is located in exon 5 (coding exon 3) of the DHCR7 gene. This alteration results from a G to A substitution at nucleotide position 376, causing the valine (V) at amino acid position 126 to be replaced by an isoleucine (I). Based on insufficient or conflicting evidence, the clinical significance of this alteration remains unclear.

This variant was observed in the ICSL laboratory as part of a predisposition screen in an ostensibly healthy population. It had not been previously curated by ICSL or reported in the Human Gene Mutation Database (HGMD: prior to June 1st, 2018), and was therefore a candidate for classification through an automated scoring system. Utilizing variant allele frequency, disease prevalence and penetrance estimates, and inheritance mode, an automated score was calculated to assess if this variant is too frequent to cause the disease. Based on the score, this variant could not be ruled out of causing disease and therefore its association with disease required further investigation. A literature search was performed for the gene, cDNA change, and amino acid change (if applicable). No publications were found based on this search. This variant was therefore classified as a variant of unknown significance for this disease.

ACMG classification criteria: PM2 moderate

This sequence change replaces valine, which is neutral and non-polar, with isoleucine, which is neutral and non-polar, at codon 126 of the DHCR7 protein (p.Val126Ile). This variant is present in population databases (rs143587828, gnomAD 0.1%). This missense change has been observed in individual(s) with clinical features of Smith-Lemli-Opitz syndrome (PMID: 24813812, 28250423). ClinVar contains an entry for this variant (Variation ID: 197725). Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) performed at Invitae indicates that this missense variant is expected to disrupt DHCR7 protein function. 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.

The DHCR7 c.376G>A variant is predicted to result in the amino acid substitution p.Val126Ile. This variant was reported in individuals with Smith-Lemli-Opitz syndrome (Cross et al. 2015. PubMed ID: 24813812; Saskin et al. 2017. PubMed ID: 28250423; Monies et al. 2019. PubMed ID: 31130284; Alharazy et al. 2021. PubMed ID: 34168679). This variant is reported in 0.12% of alleles in individuals of African descent in gnomAD. Although we suspect that this variant may be benign, at this time, the clinical significance of this variant is uncertain due to the absence of conclusive functional and genetic evidence.