The DYT1 phenotype and guidelines for diagnostic testing

Objective: To develop diagnostic testing guidelines for the DYT1 GAG deleti on in the Ashkenazi Jewish (AJ) and non-Jewish (NJ) primary torsion dystoni a (PTD) populations and to determine the range of dystonic features in affe cted DYT1 deletion carriers. Methods: The authors screened 267 individuals with PTD; 170 were clinically ascertained for diagnosis and treatment, 87 w ere affected family members ascertained for genetic studies, and 10 were cl inically and genetically ascertained and included in both groups, We used p ublished primers and PCR amplification across the critical DYT1 region to d etermine GAG deletion status. Features of dystonia in clinically ascertaine d (affected) DYT1 GAG deletion carriers and noncarriers were compared to de termine a classification scheme that optimized prediction of carriers. The authors assessed the range of clinical features in the genetically ascertai ned (affected) DYT1 deletion carriers and tested for differences between Al and NJ patients. Results: The optimal algorithm for classification of clin ically ascertained carriers was disease onset before age 24 years in a limb (misclassification, 16.5%; sensitivity, 95%; specificity, 80%). Although a pplication of this classification scheme provided good separation in the AJ group (sensitivity, 96%; specificity, 88%), as well as in the group overal l, it was less specific in discriminating NJ carriers from noncarriers (sen sitivity, 94%; specificity, 69%). Using age 26 years as the cut-off and any site at onset gave a sensitivity of 100%, but specificity decreased to 54% (63% in AJ and 43% in NJ). Among genetically ascertained carriers, onset u p to age 44 years occurred, although the great majority displayed early lim b onset. There were no significant differences between AJ and NJ geneticall y ascertained carriers, except that a higher proportion of NJ carriers had onset in a leg, rather than an arm, and widespread disease. Conclusions: Di agnostic DYT1 testing in conjunction with genetic counseling is recommended for patients with PTD with onset before age 26 years, as this single crite rion detected 100% of clinically ascertained carriers, with specificities o f 43% to 63%. Testing patients with onset after age 26 years also may be wa rranted in those having an affected relative with early onset, as the only carriers we observed with onset at age 26 or later were genetically ascerta ined relatives of individuals whose symptoms started before age 26 years.