Ischaemic cerebral small vessel disease caused by adenosine deaminase 2 deficiency syndrome

Background and purpose: Only a small proportion of cerebral small vessel disease (cSVD), a frequent cause of stroke and cognitive or motor disability in adults, is attributable to monogenic conditions. The hereditary nature of a patient's cSVD may be masked by a mild or non-informative phenotype, as single-gene disorders have a variable mode of presentation, penetrance and disease severity. Case description: An adult patient is here described with recurrent acute ischaemic strokes due to cSVD with no other phenotypic manifestation, in whom the pathogenic c.139G>A (p.G47R) missense variant in ADA2 (NM_001282225.2), consistent with the diagnosis of adenosine deaminase 2 deficiency syndrome, was detected by targeted next-generation sequencing. Conclusions: Clinical suspicion of adenosine deaminase 2 deficiency syndrome may be overlooked in stroke patients in whom other specific disease features are lacking. This case enlarges the mode of presentation of the syndrome and highlights the diagnostic potential of next-generation sequencing of known cSVD genes in young adults with recurrent small subcortical infarcts presenting with a lacunar syndrome.