家族性痴呆症(FAD)是常染色体显性遗传性疾病。有早期发病型(发病年龄65岁以下)和晚期发病型(发病年龄65岁以上)的二种病型。本文认为早期发病与淀粉前驱蛋自(APP)基因有关,APP基因位于21号染色体长臂21q11.2-21q21。晚期发病型与19号染色体长臂有关。APP基因是有18个外显子的巨大基因,发现密码子717上第2 149号碱基G→A,缬氨酸(Val)→异亮氨酸(Ile)的变化;密码子717上第2146号碱基对G→T,缬氨酸(Val)→苯丙氨酸(Phe),密码子717上第2150号 Familial dementia (FAD) is an autosomal dominant disorder. There are two types of early onset (age of onset below 65 years) and late onset (age of onset of over 65 years). This paper argues that the early onset is related to the (APP) gene and the APP gene is located on chromosome 21 long arm 21q11.2-21q21. Late onset type and chromosome 19 long arm related. The APP gene is a huge gene with 18 exons and found a change of nucleotide G → A, Val → isoleucine (Ile) at codon # 2 of codon # 717; a change of codon # 717 2146 base pairs G → T, Val → Phe, codon 717 on 2150