Sialidase (α‐N‐acetyl neuraminidase) deficiency: the enzyme defect in an adult with macular cherry‐red spots and myoclonus without dementia

A 31‐year‐old male is described who has macular cherry‐red spots, increased deep tendon reflexes and myoclonus without dementia. An older brother died at age 33 of a disease with similar symptomatology. Homogenates of cultured fibroblasts from the patient exhibited 2.6, 8.1 and 12.4 % of normal mean sialidase (neuraminidase, N‐acetyl‐neuraminosyl glycohydrolase, EC 3.21.18) activity, respectively, against 2‐(3'methoxyphenyl)‐N‐acetyl‐α‐neuraminic acid, N‐acetyl‐neuramin‐lactose and fetuin. Activities of 14 other lysosomal enzymes were within the range of normal control fibroblasts. The sialidase activities in fibroblasts from the patient's parents and children were 30 to 67 % of normal. It is concluded that this is the first proven case of a new autosomal recessive disorder resulting in cherry‐red spots, myoclonus and a sialidase deficiency.