For example, reduced levels of neurosteroids may be seen in SLOS. These are lipids which take part in signaling within the brain, and must be produced within the brain itself. They are responsible for interacting with nuclear steroid receptors, and bind to neurotransmitter-gated ion channels. Specifically, they modulate the effects of GABA and NMDA receptors, resulting in calming effects, improved memory, and more. Thus, given that some characteristics of SLOS are the opposite of these effects (hyperactivity, anxiety), a reduction in neurosteroids could influence both neurological development and behaviour. Furthermore, as outlined above, cholesterol is an important aspect in Hedgehog signaling. With lower levels of cholesterol, hedgehog proteins would not undergo the necessary covalent modification and subsequent activation. This would result in impaired embryonic development, and may contribute to the observed physical birth defects in SLOS. One particular hedgehog signaling protein, sonic hedgehog (SHH), is important in the pattern of the central nervous system, facial features, and limbs. Other hedgehog proteins may be involved in the development of the genital tract and the skeleton.The altered sterol levels in SLOS are particularly relevant to cell membranes, which are made primarily of lipids. SLOS patients may show cell membranes with abnormal properties or composition, and reduced cholesterol levels greatly affect the stability and proteins of lipid rafts. Despite their structural similarity, 7DHC is unable to replace cholesterol in lipid rafts. In addition, a lack of cholesterol contributes to the increased fluidity of the cell membrane, and may cause abnormal granule secretions.
Many patients show aggressiveness and self-injurious behaviours, and sleep disturbances are common. Specific behaviours resembling those of people with autism are often present as well as hyperactivity, which provides genetic and biological insights into autism spectrum disorders. The autistic behaviours most characteristic of SLOS patients are opisthokinesis (an upper body movement), stretching of the upper body, and hand flicking. Autism is typically diagnosed separately from SLOS using the DSM-V, and approximately 50–75% of SLOS patients meet the criteria for autism.Other behaviours associated with SLOS can be linked directly to physical abnormalities. For example, infants often show feeding problems or feeding intolerance, and patients may require increased caloric intake due to accelerated metabolism. Recurrent infections, including ear infections and pneumonia, are also common. Biochemical phenotype
Given that SLOS is caused by a mutation in an enzyme involved in cholesterol synthesis, the resulting biochemical characteristics may be predictable. Most patients have lowered plasma cholesterol levels (hypocholesterolemia). However, approximately 10% may show normal cholesterol levels,  and decreased concentrations of cholesterol are not solely indicative of SLOS. Increased levels of cholesterol precursors are also common in SLOS. In particular, elevated levels of 7-dehydrocholesterol are fairly specific to SLOS. Genetics
DHCR7
The gene encoding DHCR7 (labeled as DHCR7) was cloned in 1998, and has been mapped to chromosome 11q12-13. It is 14100 base pairs of DNA in length, and contains nine exons, the corresponding mRNA is 2786 base pairs in length (the remaining DNA sequence is intronic).