Phelan-McDermid syndrome due to SHANK3 mutation in an intellectually disabled adult male: successful treatment with lithium.

For 30 years, Phelan and co-workers described a syndrome characterised by neonatal hypotonia, global developmental delay, strongly impaired speech, sleep disturbances and hyperreactivity to sensory stimuli. This Phelan-McDermid syndrome (PMS), also presenting with symptoms from the autism spectrum and a higher risk of developing seizure disorders, may be caused by a deletion of chromosome 22q13 or by a mutation in the SHANK3 gene. Its core psychopathological phenotype comprises symptoms from the bipolar spectrum for which generally treatment with a mood-stabilising anticonvulsant in combination with an atypical antipsychotic seems to be most effective. In addition to two elsewhere published adolescent patients, we here describe in detail the history of an adult male patient with PMS caused by a SHANK3 mutation in whom successive treatment regimens with antipsychotics and mood-stabilising anticonvulsants were all ineffective. Ultimately, addition of lithium to existing olanzapine therapy led to enduring stabilisation of mood and behaviour.