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 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 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.
