According to several medical resources, Smith-Lemli-Opitz Syndrome (SLOS) is congenital and caused by mutation, e.g.

  • Smith-Lemli-Opitz syndrome is caused by mutations in the DHCR7 gene, the gene that codes for the enzyme DHCR7 that normally converts 7DHC to cholesterol in the final step of the cholesterol synthetic pathway. - Reference

  • This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition. - Reference

A friend of mine, who is 4-month pregnant, recently took a medical test giving her a high probability (1 in 8 as the test paper says) of SLO Syndrome. She has mistakenly (not knowing she was pregnant) taken Diane-35 under her doctor's prescription for 21 days in her early pregnancy. Now my question is, given that no mention has been made of drug intervention relationship with the syndrome in the medical resources, at least in those I checked, and that she already has a successful pregnancy background, can SLOS be caused due to drugs? In case of abortion, how can she make sure whether she or her husband is carrier of the syndrome for future pregnancies?

2 Answers 2


Smith-Lemli-Opitz syndrome is a genetic condition that only occurs if both parents are carriers of the mutation. For each chromosome that isn't a sex chromosome, we get one copy from each parent, so we have two copies of every gene. The "autosomal recessive pattern" means that the condition is not linked to the sex chromosomes (autosomal) and only occurs in people who have two copies (recessive), one from each parent.

The parents, as carriers, themselves don't have any symptoms because they have a "healthy" copy of the gene in addition to the mutated gene. In a combination such as that, the risk of a subsequent child showing the syndrome is 25 percent, inheriting the mutation from both parents. 25 percent of children will get two "healthy" copies, and 50 percent will get one healthy and one mutated copies, and thus be carriers themselves.

I have included a link explaining this kind of inheritance at the end.

As for Diane-35, it is an oral contraceptive. Oral contraceptives do not cause genetic mutations, either in the mother or the fetus.


Smith-Lemli-Opitz syndrome (already linked in the question, included here for completeness)

Autosomal recessive inheritance pattern

Genetics 101 with some more detailed explanation of the genetics

  • Do you mean that it will never be inherited if only one parent is carrier? Dec 5, 2015 at 14:42
  • 2
    @JasonStack yes. In strictly "recessive autosomal" inheritance, both parents need to be carriers
    – YviDe
    Dec 5, 2015 at 14:43

The following is of course, in case the diagnosis is confirmed.

SLO is an autosomal recessive pathology, which means both parents are carrier of one mutated allele of the DHCR7. They do not express the pathology because the other allele isn't mutated and this allows for a normal function of the DHCR7 gene.

This also means there is nothing that can be done about it. A birth-control pill doesn't have any impact on mutations or the genes in general, so no, it can't be due to drugs.

enter image description here

Each time this couple has a child, there is a 25% risk the child will have SLO syndrome. Because this is a high probability, they can be offered early prenatal diagnosis (so that if there's an abortion, it can be done early in the pregnancy) or pre-implantation genetic diagnosis (by selecting healthy embryos in vitro).

Edit: @YviDe answered first, but since I wrote this I'm keeping it for the "what to do for future pregnancies" part.

Image credit: Wikipedia User CBurnett (own work in Inkscape) - CC BY-SA 3.0

  • Thank you. What are R and r short for and how early into pregnancy can prenatal diagnosis take place? Dec 5, 2015 at 14:50
  • 1
    r and R are not really short for something, R represents the healthy dominant allele, and r the mutated recessive allele. You need two r and no R to express the pathology. The diagnosis can be made by sterol analysis on a chorionic villus sample, which is generally done around 10-13 weeks. Results usually come within 1-2 weeks in my experience.
    – Denn
    Dec 5, 2015 at 14:57
  • So, the test you talked about is different from that mentioned in the question? That is because it has been taken in 18th week, done by taking blood sample, but I am not sure what the test name is. Dec 5, 2015 at 15:14
  • I think they're different tests, yeah. I'm a bit confused as to what kind of SLO test can be done on maternal blood, though. Maybe something like this study, but as far as I know it's not the routine test? Or maybe the mother's had abnormalities in her hormonal blood tests, but it's not something doctors will normally search for, especially at the 18th week. Are you sure there was no amniocentesis?
    – Denn
    Dec 5, 2015 at 15:23
  • yes, amniocentesis has not been done, though the doctor recommended it, but it seems to be lengthy as Wikipedia says, "Amniocentesis and chorionic villus sampling leave very little time to make this decision (abortions become more difficult as the pregnancy advances), and can also pose severe risks to the mother and baby." Will amniocentesis, in your opinion, ensure the diagnosis? Dec 5, 2015 at 15:33

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