2. 18 trisomy syndrome caused severe deformity and died shortly after birth. The incidence rate is about 1: 3500-8000 newborns. However, in some areas or seasons, it increased significantly, reaching 1: 450-800. The ratio of female to male is 4: 1.
3. Details:
(1) Clinical manifestations: The baby was born with a low weight, with an average of only 2,243 g, and developed like a premature baby, with poor sucking, weak response, severe deformity of head, face, hands and feet, long head with prominent occipital part, round face, wide eye distance, small eyeball, cloudy cornea, slender nose, small mouth, low ear position and auricle. The deformity of the hand is very typical: clenched fist, thumb crossing other fingers, other fingers overlapping each other, nail hypoplasia, too many finger arches, about13 patients with palm penetration. The most prominent of the lower limbs is the "rocking chair foot", with a short thumb that bends to the back. The common deformities of external genitalia are cryptorchidism or labia majora and clitoris hypoplasia. 95% cases have congenital heart disease, such as ventricular septal defect and patent ductus arteriosus, which is an important cause of death. Renal malformation and hydronephrosis are also common. Children have obvious mental defects, but most of them are difficult to measure because of their short survival time.
(2) Cytogenetics: The karyotype of 80% patients is 47, XY (or XX),+18; The remaining 10% patients were chimeras, namely 46, XY (or XX)/47, XY (or XX),+18; The rest are all kinds of translocations, mainly chromosome 18 and group D. Parents are carriers of balanced translocations, which leads to the three marks of 18.
(3) prognosis; Most of the children died within 2-3 months, with an average survival of 7 1 day, and only a few patients exceeded childhood. Chimeric type has a long survival time.
4. Other trisomy syndromes are trisomy 8 and 22. All of them are accompanied by obvious developmental deformity and mental retardation. There are also a series of trisomy syndrome caused by translocation, and its clinical symptoms depend on the nature and size of extra chromosome fragments. Chromosome trisomy can be divided into two categories: one is trisomy (duplication) of a chromosome fragment, accompanied by other chromosomal abnormalities (such as deletion and translocation), and the phenotype of this trisomy is complex, often accompanied by some symptoms of duplication and deletion; The other is a simple duplication or trisomy of a chromosome fragment, which is extremely rare in humans.