In this study we present an 11 year old boy in which we detected a de novo nonsense mutation in β-catenin (CTNNB1). Mutations of CTNNB1 were recently reported to be associated with a rare ID syndrome with consistent clinical features including significant motor delay with hypotonia of the trunk, progressive distal hypertonia/spasticity of the legs, speech impairment, behavioral anomalies, frequently microcephaly and overlapping dysmorphic facial features [1–4]. Here, CTNNB1 is linked to microcephaly.