What is Smith-Lemli-Opitz Syndrome (SLOS)?

Smith-Lemli-Opitz Syndrome (SLOS) or 7-Dehydrocholesterol reductase deficiency

is a developmental, metabolic, and a congenital (by birth) multiple anomaly condition which is the result of an abnormality in the synthesis of cholesterol or cholesterol metabolism. The abnormality is the deficiency of the enzyme 7-dehydrocholesterol reductase (DHCR7), the final enzyme in the cholesterol synthesis pathway that helps in the conversion of 7-dehydrocholesterol (7DHC) to cholesterol. In other words, people with this syndrome do not have the ability to produce enough cholesterol required for the normal development and growth of body.

The syndrome was named after David Smith, Luc Lemli, and John Opitz, the three geneticists who first described it in the year 1964.

According to an estimate, 1 in 20,000 to 50,000 newborns may be affected by this condition. Boys are more prone to it than girls. The condition is common in whites or Caucasians with European ancestry, especially from the countries of Czech Republic and Slovakia.

Significance of Cholesterol:

Cholesterol, a waxy, fat-like substance obtained from some of the foods consumed and produced in the body is a necessary factor for normal embryonic development and growth after birth as the child ages. It has a key role in the production of digestive acids and some of the important hormones. Moreover, it is a vital structural component of cell membranes (outer lining of a cell) and myelin sheath (the protective sheath or layer that encloses the nerve cells).

Characteristic Features of Smith-Lemli-Opitz Syndrome:

People with this syndrome are characterized by:

  • Cholesterol is one of the major parts of the tissues and cell membranes in the brain. Therefore, if a person is not able to produce required amounts of it, the person may become

    mentally retarded.

  • Prenatal and postnatal retardation in growth.

  • Small head or microcephaly.

  • Children with this syndrome may have

    cleft palate, behavioral problems, difficulty in learning (autism), dysmorphic facial features, small head, squint eyes, ptosis or drooping eyelids.

  • Some other features specific to this syndrome are

    finger abnormalities such as extra toes and/or fingers, a condition known as polydactyly and syndactyly or fusion of 2nd and 3rd toes.

  • Infants may

    experience feeding difficulties

    and usually

    have a weak muscle tone also known as hypotonia.

  • Both in males and females external genetalia (gential or sex organs) may be underdeveloped.

  • Vital organs of the human body such as

    heart, kidneys, lungs etc may also be affected.

Causes & Genes Associated with Smith-Lemli-Opitz Syndrome:

This syndrome may run in families. It is inherited by the child in an autosomal recessive mode of inheritance. This means both the gene copies in each cell have mutations. Although the parents of the affected child carry one copy each of the mutated genes, they do not show any of the above mentioned signs and symptoms. They are known as carriers, people with 1 mutated gene copy and 1 good gene copy.

Mutations (permanent changes in the DNA) in the DHCR gene result in this syndrome. The enzyme responsible for cholesterol production, 7-dehydrocholesterol reductase (DHCR7), gets affected as a result of the mutations. This in turn does not allow the cells to generate required amounts of cholesterol for the body. Eventually, the toxic by-products of cholesterol synthesis pile up in various body parts such as nervous system, blood stream etc. These piled up toxins in combination with low cholesterol levels hamper the normal growth and development of the body parts.

Treating Smith-Lemli-Opitz Syndrome:

  • Cholesterol Supplementation a��

    Because the syndrome is associated with lower than normal cholesterol levels, supplying cholesterol in the form of crystalline cholesterol or egg yolk either in a water suspension or an oil based suspension is usually suggested by the doctors.

  • Children with problems in feeding may require


    , a feeding tube that is inserted into the stomach wall to supply food.

  • Surgical intervention may be required to correct some abnormalities like polydactyly or syndactyly, cleft palate, genital defects etc.

If family history indicates the presence of this disease, pregnant women can get a fetal ultrasound done which detects malformations of the brain, limbs, kidneys, heart, improper genitals, slow growth, cleft palate etc.

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