Smith-Lemli-Opitz-Syndrom

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Smith-Lemli-Opitz syndrome (SLOS) also known as 7-dehydrocholesterol reductase deficiency is an inborn error of cholesterol synthesis.

Epidemiology

The estimated incidence is at 1:20000-40000 live births. Prevalence may be greater in Nordic countries.

Clinical presentation

There are many which include:

CNS
- intellectual disability
- hyperexcitability
- microcephaly
- hypotonia
- holoprosencephaly
craniofacial
- blepharophimosis
- epicanthus
- micrognathia
- low set ears
limb
- postaxial polydactyly
- syndactyly: usually 2 and 3 toes
congenital cardiac anomalies
congenital urogenital anomalies
- hypospadias
- cryptorchidism
intra-uterine growth restriction (IUGR)

Pathology

The condition often results from a mutation in the DHCR7 gene on chromosome 11q12-13 which reduces the activity of 7-dehydrocholesterol reductase. Rarely there may be a mutation in chromosome 7q32.1. There is then a lack of cholesterol production as well as a build-up of potentially toxic by-products of cholesterol production which accumulate in the blood and other tissues. It was traditionally classified into 2 types although they are not considered to represent the spectrum differing severity.

Genetics

It carries an autosomal recessive inheritance .

Associations

Hirschsprung disease

Markers

low maternal low estriol : although nonspecific

Radiographic features

Antenatal ultrasound

There may be increased nuchal translucency in 1trimester as an early feature . Antenatal ultrasound may also be able to detect some of the above clinical features.