Pediatric Medical Genetics - S.I. Smiyan 2003

Chromosomal diseases
Autosomal anomalies

Autosomal anomalies can be of various types, including trisomies, monosomies, structural aberrations of individual Chromosomes (such as translocations, deletions, fragmentations, and ring chromosomes), and mosaicism. Disturbances in large and medium-sized chromosomes resulting from non-disjunction during Meiosis and The formation of trisomy lead to fetal damage incompatible with life, and are a major cause of spontaneous abortions and stillbirths. This accounts for 6–8% of spontaneous abortions. According to Carr and Stonova, the frequency of abnormal karyotypes among spontaneously aborted embryos ranges from 21–22%. The average gestational age prior to Spontaneous Abortion in cases of abnormal karyotypes is 86 days. Chromosomal aberrations are particularly frequent in spontaneous miscarriages During the first three months of Pregnancy. Among quantitative Chromosomal Disorders, trisomies are the most common. In the postnatal period, full trisomies for only a few chromosomes are compatible with survival, even for a short duration—specifically chromosomes 8, 9, 13, 18, 21, and 22. Furthermore, cases of mosaicism are frequent for autosomes 8 and 9, which undoubtedly mitigates the lethal effect of genetic material imbalance.

Complete monosomy in newborns is an exceptionally rare phenomenon, not conclusively proven even for the smallest chromosome 21. Complete monosomies are apparently non-viable as early as the gamete and zygote stages for all autosomes, given that reports of such findings in spontaneous abortion material are isolated and known only for a relatively small number of autosomes.

Structural rearrangements are characteristic of all autosomes without exception. For the majority of autosomes, it has been possible to identify a relative clinical Specificity in the phenotypic deviations caused by chromosomal structural abnormalities. However, observation and accumulation of experience are still ongoing, as nature is inexhaustible in generating novel pathological cases, while the resolution of Cytogenetic Methods is continuously improving.