For geneticists the fascinating fact about the Old Order Amish, one of the sects of the Pennsylvania Dutch country's "Plain People," is that they all are descended from about 200 immigrants of 200 years ago. A few Amish leave the ancestral acres and simple (no motors, no worldly entertainments) way of life, but virtually no new blood has been introduced to create genetic confusion. For such a group, to survive is to inbreed, and the Amish have more than survived; they now number 44,000. In 1963, to take advantage of this unique opportunity into the land of the black buggy, the beard and the modest bonnet went Johns Hopkins' Dr. Victor A. McKusick, an epidemiologist as well as a geneticist. And last week at Bar Harbor out came a detailed report on two forms of dwarfism, one recognized only a generation ago, the other brand-new to medical science.
Samuel's Seed. The first form is confined, so far as the U.S. is concerned, to the region of Pennsylvania's Lancaster County around a town called Intercourse. Named the "Ellis-van Creveld Syndrome" after the Scottish and Dutch pediatricians who first reported it in 1940, it has no common name and is so uncommon elsewhere in the world that only about 50 cases had been reported until McKusick's Hopkins team moved into Pennsylvania. There they found proof of at least 49 cases since 1860, with 24 still living. Most exciting, genetically at least: the Amish keep such exact genealogical records that McKusick was able to trace all 60 parents to whom the 49 were born. And all were descended from a single immigrant and his wife.
It was in 1744 that Samuel King arrived in the U.S. He or his wife (it is impossible now to tell which) had one chromosome marred by a defective gene. Since the gene is a recessive, none of their children showed any sign of its curse, nor did their children's children. If they had married normally into the U.S. population at large, probably the gene would have stayed quiescent, with only an infinitesimal chance of sad results. But within a couple of generations, King's descendants began to marry second or third cousins. Eventually, it had to happen: a man who carried the gene married a cousin, of some degree or remove, who also carried it. Their unfortunate offspring inherited a double dose of the bad gene.