THE RAPID GROWTH of human cytogenetics imposes, as a corollary, the progressive restriction of the scope of a talk on this subject. Two years ago, a quarter of an hour was sufficient for a general survey; today, a whole hour is filled with one topic only. Without being a prophet, it can be seriously foreseen that some day, a Blackfan Lecture restricted to "the genic content of the short arm of chromosome 22" will be considered a very brief summary of the current knowledge.

I would like to discuss the general implications of the available data on autosomal disorders. Chromosomes are divided into sex chromosomes and non-sex chromosomes, which are generally called autosomes. My subject can be considered under three points of view: the recognition of autosomal disorders, the mechanism of their production and, finally, the practical or heuristic use of this knowledge, as it enables more to be learned.


The Numerical Abnormalities

The numerical abnormalities are no longer limited to classic mongolism, with its 47 chromosomes and its trisomy for No. 21.1-3

The trisomy for chromosome 17, in which there occurs a typical deformity of the head, a small mandible, low set ears, other nonspecific malformations of heart, hands and feet, and severe mental retardation, is also quite classic. Possibly more than 25 different patients suffering from this disease are now known.

The 13-15 trisomy with eyeball defects, polydactyly, cardiopathy, and mental defect, together with deformities of lips, palate, skin, and ears is also well established.

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