Objective To describe the clinical and genetic findings in a family affected by neurodevelopmental delay and cerebellar ataxia.

Methods The affected mother and her two children underwent clinical assessments followed by radiological, neurophysiological and cytogenetic investigations.

Results All three affected members exhibited varying degrees of delay in attaining motor and cognitive milestones, along with learning difficulties and cerebellar ataxia. All three harboured a new 670 kb deletion of chromosome 12q21. Two genes, KCNC2 and ATXN7L3B, lie within the deleted region.

Conclusions This family's complex phenotype is associated with a new chromosomal deletion, which suggests potential roles for the two genes, KCNC2 and ATXN7L3B, in human neurological disease.