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We have been able to trace 40 cases of classical Friedreich's disease from 14 previously unrelated French Canadian kindreds to one common ancestral couple arriving in New France in 1634: Jean Guyon and Mathurine Robin. One member of this couple presumably introduced one gene for Friedreich's disease into the French Canadian population. This gene has now been traced over 12 generations to both parents of the present cases. We plan to use this knowledge to study the spectrum of clinical manifestations of this gene and to carry out gene chromosomal localization studies, using the techniques of linkage and of molecular biology. Such studies in rare autosomal recessive disorders have previously been judged to be almost impossible.

The physician exposed to a large number of patients with a recessive form of ataxia, will occasionally observe slower progression forms which lack many of the severe features or cardinal symptoms of Friedreich's disease. We have studied 31 such cases in Acadians of the Maritime Provinces of Canada, and in their separated "cousins" from Louisiana, now called "Cajuns". These patients are compared to a consecutive series of 22 Friedreich's disease cases in French Canada. It is shown that the age of onset is slightly later, but the progression much slower and the age at death older in the Acadian patients. These cases develop signs of pyramidal and posterior column involvement gradually and later than the classical Friedreich. As a result, pes cavus and scoliosis are less marked, as well as muscle weakness and cardiomyopathy. On the other hand, the rate of progression of areflexic ataxia, the "core disease", is identical in both groups. The main difference in progression rates of the disorders occurs after 10-12 years of evolution, thus after the period of hormono-ponderal growth. These differences, coupled to the diverging genetic and genealogical backgrounds, are sufficiently large for the presumption of distinct disorders. Whether they are due to allelic mutations, linked but different genes, genes affecting the same metabolic pathway, but elsewhere or to completely distinct entities, will have to be left to further studies, but their existence in completely different populations and milieux is worthy of report.

We present a working and flexible classification of inherited ataxic syndromes based on the use of simple tools available to every clinician: a good history (particularly pinpointing the age of onset, the rate of progression and the mode of inheritance) and a neurological examination (identifying the presence of ataxia, deep tendon reflexes in the knee, optic nerve, retinal and/or 8th nerve signs). This classification is easily coded for computer translation on any personal computer. The place occupied by a given disorder may, by contiguity, give a clue to its pathophysiology.