According to the obtained data, 16 affected patients were identified in four consecutive generations in Family 1 (Fig. 1a). Acceptable data on the course of the disease were obtained from nine patients, three of whom were examined by the authors, while in six cases the course was reconstructed pursuant to medical records and information obtained from their relatives and physicians.

In Family 2 (Fig. 1b), nine affected members in four consecutive generations were identified. Acceptable data on the course of the disease were obtained from seven patients, four of whom were examined by the authors, while in three the course was reconstructed pursuant to medical records and information obtained from their relatives and physicians.

Age at onset of the affected members of Family 1 was 31.8 ± 10.7 years (range 27-60 years; median 30 years), while in Family 2 it was 45.0 ± 8.4 years (range 35-55 years; median 42 years; p<0.01), without differ­ence in the initial expression of the SCA1 symptoms. In as many as eight out of nine of the investigated patients in Family 1, the disease started between the ages of 27 and 30, and in only one case the onset was substantially delayed (60 years). Variability of age at onset was significantly higher in Family 2, where out of seven studied patients the earli­est case of SCA1 started at the age of 35, or 36 in one patient, 42 in two, 50 in one and 55 in two patients. For six deceased patients from Family 1, age at the time of death was 45.4 ± 16.6 years (range 33-74 years), while in three patients from Family 2, this age was 56 years (51, 58 and 59 years, respectively) The duration of SCA1 for the patients who died was 10.8 ± 4.1 years (range 5-15 years) for Family 1, while SCA1 lasted 9 years (3, 11 and 13 years, respectively) in Family 2. The ages of the unaffected carriers in Family 1 were 25, 30 and 41 years, and in Family 2 they were 17, 32 and 49 years.

The mean number of CAG repeats in the mutated SCA1 gene in two affected members and three unaffected carriers from Family 1 was 47.8 ± 4.8 (range 42-54; median 47). However, in the proband whose symp­toms started at the age of 27, the number of CAG repeats was 64. In Family 2, we have tested four affected members and found two unaffected carriers of the mutated gene, whose CAG repeat number was similar (47.7 ± 2.6; range 45-51; median 48). The mean number of CAG repeats in the normal SCA1 alleles in tested members in Family 1 was 28.2 ± 1.9 (range 26-31; median 28), and in Family 2 it was 28.4 ± 2.6 (range 26-33; median 28).

Haplotype analysis revealed that expanded SCA1 alleles in Family 1 were associated with 6 dinucleotide repeats in the D6S337 locus, while in Family 2, expanded SCA1 alleles co-segregated with five repeats at the same locus.