Smith-Lemli-Opitz syndrome (SLOS)

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

Smith-Lemli-Opitz syndrome is a variable genetic disorder characterized by slow growth both before and after birth. It is thought to occur in anywhere from 1 in 20-60,000 live births.

This rare disease is also known as multiple congenital anomaly disorder, presenting with intellectual disability.

The syndrome is most common in Caucasians of Central European descent. But extremely rare amongst African and Asian populations.

What gene changes cause Smith-Lemli-Opitz syndrome (SLOS)?

Mutations in the DHCR7 gene lead to a deficiency of enzyme 7 dehydrocholesterol reductase. This leads to low cholesterol levels and the resulting Smith-Lemli-Opitz syndrome. The syndrome is inherited in an autosomal recessive pattern.

Autosomal recessive inheritance means an affected individual receives one copy of a mutated gene from each of their parents, giving them two copies of a mutated gene. Parents, who carry only one copy of the gene mutation will not generally show any symptoms, but have a 25% chance of passing the copies of the gene mutations onto each of their children.

What are the main symptoms of Smith-Lemli-Opitz syndrome (SLOS)?

Symptoms may vary from mild to moderate, but the main symptoms of Smith-Lemli-Opitz syndrome are behavioral and learning problems. Most individuals with the syndrome receive a separate diagnosis of autism or display autistic tendencies. Self-injurious and aggressive behaviors are also often present in individuals with the syndrome.

Typical facial characteristics of the syndrome include a broad nasal bridge, small chin, low set ears, high arched palate, long upper lip, small jaw, large ears, and drooping eyelids. Some individuals are born with extra fingers and or toes, and a fusing of the 2nd and 3rd toes is a common feature of the syndrome.

Other symptoms include chronic sleep problems, photosensitivity, other sensory issues, genital abnormalities, and multiple birth defects (congenital disabilities), including those relating to the heart, gastrointestinal tract, lungs, and kidneys.

How does someone get tested for Smith-Lemli-Opitz syndrome (SLOS)?

The initial testing for Smith-Lemli-Opitz syndrome can begin with facial analysis screening, through the FDNA Telehealth telegenetics platform, which can identify the key markers of the syndrome and outline the need for further testing. A consultation with a genetic counselor and then a geneticist will follow. 

Based on this clinical consultation with a geneticist, the different options for genetic testing will be shared and consent will be sought for further testing.   

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