The presentation of individuals with SLOS is broad ranging from a less severe disorder with behavioural and learning difficulties to a lethal syndrome with miscarriage, stillbirth or death in the first weeks of life. Individuals often have typical facial features, including microcephaly, a small upturned nose, droopy upper eyelids and micrognathia (undersized jaw). Other abnormalities may include:
- cleft palate (see entry Cleft Lip and/or Palate)
- abnormalities of the fingers and toes, including polydactyly (an additional digit) and syndactyly of the second and third toes. (where two or more digits are fused together)
- abnormalities in development of the heart, kidneys, liver and lungs
- underdevelopment of external genitalia occurs in males.
In surviving infants, slow growth and poor weight gain is usual and feeding via a gastrostomy (a tube into the stomach) may be required. As the infant gets older, severe learning difficulties (see entry Learning Disability) usually become evident. In addition, individuals with SLOS tend to display hyperactivity, sleep disturbance, autistic-type behaviour (see entry Autism Spectrum disorders, including Asperger syndrome) and have a tendency to self-injure. Individuals are very rarely able to live independently.