DHCR7 rs28941772: Smith-Lemli-Opitz Syndrome Carrier Status
The genetic variant rs28941772, historically described as c.964-1G>C or IVS8-1G>C, is a well-characterized pathogenic splice site mutation in the DHCR7 gene. Carrying a single copy of this variant confers carrier status for Smith-Lemli-Opitz syndrome (SLOS), a rare autosomal recessive metabolic disorder. Carriers typically show no symptoms, but inheriting two altered copies can impair endogenous cholesterol biosynthesis and lead to multisystem developmental features.
What each genotype means
Typical risk
You carry two reference copies of this DHCR7 locus and do not carry the c.964-1G>C pathogenic splice variant. This result indicates you are not a carrier for this specific cause of Smith-Lemli-Opitz syndrome. Because carrier screening evaluates specific variants, it does not completely eliminate the possibility of rare, unassayed variants elsewhere in the DHCR7 gene.
Carried by over 98% to 99% of people across most global populations.
SLOS carrier status
You carry one copy of the pathogenic c.964-1G>C (IVS8-1G>C) variant, making you an asymptomatic carrier of autosomal recessive Smith-Lemli-Opitz syndrome. Carriers do not experience classic symptoms of the disorder, as one functional copy of the DHCR7 gene typically maintains sufficient enzyme activity. Reproductive risk is primarily relevant if your partner is also a carrier for a pathogenic DHCR7 variant, which can be evaluated through reproductive genetic counseling.
Carried by approximately 1% to 2% of individuals of European ancestry and around 0.7% of African Americans; it is much less common in East Asian populations.
High risk for SLOS
This genotype indicates two copies of the c.964-1G>C null splice variant in DHCR7, a pattern strongly associated with Smith-Lemli-Opitz syndrome. In medical literature, homozygosity for this severe variant disrupts cholesterol biosynthesis and is associated with severe multi-system congenital features or high early mortality. Clinical confirmation and consultation with a medical geneticist are essential to contextualize these genetic findings.
Extremely rare across all populations, occurring in fewer than 1 in 100,000 individuals globally.
Variant Architecture and Molecular Impact
The variant rs28941772 represents a single-nucleotide change from guanine (G) to cytosine (C) located at the canonical splice acceptor site of intron 8 in the DHCR7 gene, formally designated as c.964-1G>C. Canonical splice acceptor sites contain highly conserved sequences essential for directing the cellular splicing machinery to join coding exons correctly. Molecular and functional studies indicate that altering this critical nucleotide disrupts standard RNA processing, triggering an alternative splice site 134 base pairs downstream. This shift inserts abnormal sequence, causes a frameshift, and introduces a premature termination codon. Consequently, transcripts generated from this altered allele either undergo nonsense-mediated mRNA decay or produce a truncated, non-functional protein. This severe loss-of-function effect classifies the variant as a null allele in cholesterol biosynthesis.
Biological Role of the DHCR7 Gene
The DHCR7 gene provides instructions for producing 7-dehydrocholesterol reductase, an enzyme that catalyzes the final step in the biochemical pathway of cholesterol biosynthesis. This enzyme reduces the double bond at carbon-7 of 7-dehydrocholesterol (7-DHC) to produce cholesterol, which is an essential structural constituent of mammalian cellular membranes. Beyond maintaining membrane fluidity and specialized lipid rafts, cholesterol acts as a precursor for bile acids, steroid hormones, and oxysterols. It also plays an indispensable role in embryonic development by covalently modifying Hedgehog family proteins, including Sonic Hedgehog, which dictate pattern formation in organogenesis, limb patterning, and neural tube development. When DHCR7 function is severely deficient, cells accumulate toxic 7-DHC precursors and produce insufficient cholesterol, resulting in the complex congenital abnormalities characteristic of Smith-Lemli-Opitz syndrome.
Carrier Status and Smith-Lemli-Opitz Syndrome
Smith-Lemli-Opitz syndrome is inherited in an autosomal recessive pattern. Clinical and molecular genetic databases, such as ClinVar and GeneReviews, consistently document rs28941772 as the most common pathogenic variant involved in SLOS, accounting for approximately 30% of all disease alleles in affected populations. Individuals who possess one copy of the variant (heterozygotes) are designated carriers. Decades of biochemical evaluation demonstrate that carriers usually maintain sufficient functional enzyme from their single functional DHCR7 allele to produce adequate cholesterol and remain entirely asymptomatic. However, if both parents are carriers, each pregnancy faces a 25% statistical probability of inheriting two altered copies. Individuals who are homozygous or compound heterozygous for null variants like c.964-1G>C typically exhibit severe forms of SLOS or experience early developmental arrest.
Population Distribution and Ancestry Patterns
The c.964-1G>C variant exhibits significant variation across different world ancestries, reflecting a notable founder effect in specific geographic groups. In the Genome Aggregation Database (gnomAD), the overall allele frequency across unselected reference populations is approximately 0.0039 to 0.0074. The variant is observed at its highest frequencies among populations of European ancestry, particularly those of Central and Eastern European origin, as well as in individuals of Ashkenazi Jewish descent, where allele frequencies can reach approximately 0.012. Across these higher-prevalence groups, the carrier frequency is estimated at roughly 1 in 43 to 1 in 100 individuals (1% to 2.3%). In contrast, the variant is exceptionally rare or absent in reference cohorts of East Asian, African, and South Asian ancestry.
Navigating Carrier Status and Reproductive Planning
Identifying an altered allele at rs28941772 is informative for reproductive carrier screening rather than personal diagnostic medicine. Heterozygous carriers do not require medical intervention, dietary cholesterol adjustments, or surveillance for metabolic illness, as they are not affected by SLOS. Instead, the utility of this information lies in family planning. Because autosomal recessive inheritance requires mutations on both parental alleles to cause disease, an individual's reproductive risk depends directly on the genetic status of their partner. Anyone learning they carry rs28941772 may wish to discuss the finding with a board-certified genetic counselor or medical geneticist. These professionals can explain expanded carrier screening, evaluate familial risks, and outline available reproductive options, including pre-implantation genetic testing or prenatal diagnostics.
How common is this variant?
The rs28941772 alternate allele has an overall gnomAD frequency of approximately 0.39% to 0.74%, reaching roughly 0.6% in general European ancestries and up to 1.2% in Ashkenazi Jewish populations, corresponding to a carrier frequency of 1% to 2.3%. It is exceedingly rare in individuals of African and East Asian descent.
Frequently asked questions
What does being a carrier for rs28941772 mean for my health?
Being a carrier means you have one non-working copy of the DHCR7 gene and one normal copy. Because your working copy produces enough functional enzyme to synthesize cholesterol normally, carriers generally experience no related medical symptoms or developmental issues.
Does carrying the rs28941772 variant cause high or low cholesterol?
No, carrying a single altered copy does not typically cause clinically abnormal cholesterol levels. Standard blood lipid panels in carriers remain within standard reference ranges because the remaining healthy allele compensates adequately.
What is the likelihood that my child will have Smith-Lemli-Opitz syndrome?
A child can only develop Smith-Lemli-Opitz syndrome if both biological parents carry a pathogenic variant in the DHCR7 gene. When both parents are confirmed carriers, each pregnancy has a 25% chance of inheriting both variants and being affected, a 50% chance of being a healthy carrier, and a 25% chance of inheriting two normal copies.
Is this variant known by any other scientific names?
Yes, in clinical genetics literature this variant is frequently referenced as c.964-1G>C, referring to its position on the coding transcript NM_001360, or by its legacy name IVS8-1G>C, denoting its location in intron 8.
Sources & further reading
Educational information only, last refreshed 9/9/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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