[Clinical features and COL4A1 genotype of a toddler with hereditary angiopathy with nephropathy, aneurysms and muscle cramps syndrome]. 
Hereditary angiopathy with nephropathy, aneurysms and muscle cramps (HANAC) syndrome is an autosomal dominant genetic disease caused by COL4A1 gene mutation, with major clinical manifestations of white matter lesion, aneurysm, retinal artery tortuosity, polycystic kidney, microscopic hematuria and muscle cramps.  This article reports the clinical features and genotype of one toddler with HANAC syndrome caused by COL4A1 gene mutation.  The boy, aged 1 year and 8 months, had an insidious onset, with the clinical manifestations of pyrexia and convulsion, white matter lesions in the periventricular region and the centrum semiovale on both sides, softening lesions beside the left basal ganglia, retinal arteriosclerosis, microscopic hematuria and muscle cramps.  Whole exome sequencing revealed a pathogenic de novo heterozygous mutation in the COL4A1 gene, (NM_001845) c.4150+1(IVS46)G>T, and therefore, the boy was diagnosed with HANAC syndrome.  COL4A1 gene mutation detection should be performed for children with unexplained white matter lesion, stroke, hematuria, polycystic kidney, cataract and retinal artery tortuosity or families with related history.