What else is it called?
- Sterol C5-desaturase deficiency
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What causes it?
This disorder is caused by a fault in the SC5D gene which provides instructions for an enzyme called 3-beta-hydroxysteroid-delta-5-desaturase. This enzyme is needed for a chemical reaction in your body which converts a molecule called lathosterol into a sterol called 7-dehydrocholesterol. The reaction is involved in the formation of cholesterol. A faulty gene means that you do not produce enough of the enzyme and this reaction cannot take place. This prevents the proper formation of cholesterol, which is an essential lipid needed by your body for several roles and functions including the development of certain steroid hormones and bile acids.
How common is it?
This is an extremely rare disorder, less than five cases have been reported in the literature so far.
What are the signs and symptoms?
Symptoms are present at birth, and may include:
- A weak muscle tone – babies may appear to be ‘floppy’ (hypotonia)
- Failure to grow or gain weight at the expected rate
- A small head (microcephaly)
- Narrowing of the temples
- Drooping of the eyelids (ptosis)
- Broad nasal tip
- Puffy cheeks
- Small teeth
- Extra fingers or toes (polydactyly)
- Fusion of toes
- Club feet
During childhood, you are likely to notice delays in reaching developmental milestones such as crawling, talking, or walking as well as some degree of learning disability. These are common symptoms in this condition.
Other symptoms may include:
- Clouding of the cornea
- Hearing loss
- Underdeveloped gums
- Kidney malformations
- Neurological conditions such as muscle spasms
- Varying degrees of liver disease
- Genital development problems
How is it diagnosed?
Diagnosis is based on a range of specialised tests including blood and urine tests and tests on skin cells. Genetic testing can confirm diagnosis. Prenatal diagnosis may be possible if the disorder is known within the family.
This disorder is similar to another inherited metabolic disorder called Smith-Lemli-Opitz syndrome.
Can it be treated?
There is no cure for Lathosterolosis. Treatment includes cholesterol supplements and a reduction of 7-hydrocholesterol. Your specialist and a dietitian will advise you on how this can be achieved. Surgery may be needed to correct fused toes. Regular follow ups, examinations, and monitoring are important in the management of this condition.
Prognosis is generally poor. However, treatment may increase life expectancy and prevent neurological damage.
Do my family need to be tested?
This disorder can only be passed on to a child if both parents have a copy of the faulty gene. This is called autosomal recessive inheritance. A person who has a copy of the faulty gene is known as a carrier.
If both parents are carriers, their child has a one in four (25%) chance of inheriting the disorder, and a one in two chance (50%) of being a carrier. This is the same for each child the parents have.
If the child only inherits one copy of the faulty gene, they will be a carrier but will not have the disorder. In some rare cases, carriers have had mild symptoms of the disorder for which they carry the faulty gene.
Once you receive a diagnosis, you can speak to a genetic counsellor. They can provide further information about inheritance and can also tell you about genetic testing for the rest of your family.