一个除双侧小眼球、小角膜外,全身无任何异常体征的五个月婴儿的全部核型中,均有一个额外的小染色体。其姐姐双侧眼球、角膜大小与其一样,夭折于产后两个月。整个家系调查发现:患者母亲、外祖母的全部核型中,均携带有一个额外小染色体。G、C式显带、银染法证实,祖孙三代所携带的额外小染色体完全一样。先证者的异常体征推测是额外小染色体携带的致畸基因被激活后的表型效应。 An extra minichromosome is present in all karyotypes of five-month-old infants except for the small ocular and the cornea with no abnormalities in the body. Its sister both eyes, the corneal size the same, died in postpartum two months. The entire pedigree survey found: Patient mother, grandmother all karyotype, carry an extra small chromosome. G, C-banding, silver staining confirmed that the extra small chromosomes carried by the three generations of grandparents and grandchildren exactly the same. Abnormal signs of probands are presumed to be phenotypic effects after the activation of the teratogenic genes carried by extra small chromosomes.