Children with CdLS usually have slow or very slow development and significant learning disability. Many have psychological and behavioural problems, including autistic spectrum disorders (see entry Autism Spectrum disorders, including Asperger syndrome), poor sleep, social anxiety, compulsive behaviour and self-injurious behaviour.
Many children have limb abnormalities, ranging from having small hands and particularly short thumbs in mild cases, to almost complete absence of the forearms in severe cases. Affected children will often have an unusual marbled appearance to the skin on their arms and legs, particularly when they are cold.
Almost all the children have similar facial features, including hirsutism (excessive hair), thin and arched eyebrows that often meet in the middle, long eyelashes, low-set ears, widely spaced teeth, a short upturned nose and down-turned lips.
Medical complications are very common in CdLS, including feeding and bowel problems, particularly gastro-oesophageal reflux (GERD). Heart defects are also common, affecting at least ten per cent of those with CdLS. Most children have hearing problems and seizures (see entry Epilepsy) are another common feature.