Biaoyang Lin

A Worldwide Study of the Huntington's Disease Mutation: The Sensitivity and Specificity of Measuring CAG Repeats

BACKGROUND Huntingtons disease is associated with an expanded sequence of CAG repeats in a gene on chromosome 4p16.3. However, neither the sensitivity of expanded CAG repeats in affected persons of different ethnic origins nor the specificity of such repeats for Huntingtons disease as compared with other neuropsychiatric disorders has been determined. METHODS We studied 1007 patients with diagnosed Huntingtons disease from 565 families and 43 national and ethnic groups. In addition, the length of the CAG repeat was determined in 113 control subjects with a family history of Alzheimers disease (44 patients), schizophrenia (39), major depression (16), senile chorea (5), benign hereditary chorea (5), neuroacanthocytosis (2), and dentatorubropallidoluysian atrophy (2). The number of CAG repeats was also assessed in 1595 control chromosomes, with the size of adjacent polymorphic CCG trinucleotide repeats taken into account. RESULTS Of 1007 patients with signs and symptoms compatible with a diagnosis of Huntingtons disease, 995 had an expanded CAG repeat that included from 36 to 121 repeats (median, 44) (sensitivity, 98.8 percent; 95 percent confidence interval, 97.7 to 99.4 percent). There were no significant differences among national and ethnic groups in the number of repeats. No CAG expansion was found in the 110 control subjects with other neuropsychiatric disorders (specificity, 100 percent; 95 percent confidence interval, 95.2 to 100 percent). In 1581 of the 1595 control chromosomes (99.1 percent), the number of CAG repeats ranged from 10 to 29 (median, 18). In 12 control chromosomes (0.75 percent), intermediate-sized CAG sequences with 30 to 35 repeats were found, and 2 normal chromosomes unexpectedly had expanded CAG sequences, of 39 and 37 repeats. CONCLUSIONS CAG trinucleotide expansion is the molecular basis of Huntingtons disease worldwide and is a highly sensitive and specific marker for inheritance of the disease mutation.

Genomic organization of the human α-adducin gene and its alternately spliced isoforms

Abstract The cDNA for the human α-adducin gene has been cloned, and different alternately spliced forms have been identified. We report the complete genomic organization of the human α-adducin gene and these alternately spliced forms. The human α-adducin gene, spanning approximately 85 kb, consists of 16 exons ranging in size from 34 to 1892 bp. One of the spliced forms of the human α-adducin gene results from alternate use of the 5′ splice donor site for exon 10, while another results in a truncated protein following insertion of 34 bp comprising exon 15, followed by a premature stop codon. This alternate spliced form of α-adducin is predicted to result in an altered carboxyl terminus that would eliminate a protein kinase and calmodulin binding site. Seven nucleotide substitutions and 4 insertion/deletions were also identified. The 5′ region of the human α-adducin gene contains one Sp1 site, two AP2 sites, and two CAAT boxes. No TATA box was apparent, consistent with features of a housekeeping gene. We have mapped another cDNA within the first intron of the human α-adducin gene, suggesting overlapping genes in this 4p16.3 genomic region.