Germline mutations in Peruvian patients with hemophilia B: pattern of mutation in AmerIndians is similar to the putative endogenous germline pattern.

Exogenous (e.g., environmental) mutagens produce characteristic patterns of mutation. In contrast, endogenous mutation processes likely are associated with an invariant pattern of mutation. Analysis of factor IX gene mutations among large samples of hemophilia B patients from multiple, widely divergent geographic and ethnic populations reveals a remarkably constant mutational pattern, suggesting that the primary germline mutational process results from endogenous processes rather than environmental mutagens. To test this hypothesis further, we have initiated a study of hemophilia B patients from Peru because relatively large populations of AmerIndians can be found with low admixtures of other races. To determine if the factor IX (FIX) germline mutational pattern in AmerIndians differs from the common and putative endogenous pattern, FIX gene mutations were characterized in an initial sample of 10 AmerIndian Peruvian patients with hemophilia B. A minimum of 2.2 kb of the FIX gene was examined by PCR and direct sequencing of all eight exons, the splice junctions, and the promoter region. The pattern of germline mutation in AmerIndians was similar to the pattern of FIX germline mutations from larger U. S. Caucasian or Mexican Hispanic samples (P=0.55 and 0.63, respectively). The similar pattern in this initial sample of the Peru AmerIndian population provides additional support for the inference that the FIX germline mutational pattern results from predominantly endogenous processes rather than exogenous mutagens.

Screening the monoamine oxidase B gene in 100 male patients with schizophrenia: a cluster of polymorphisms in African-Americans but lack of functionally significant sequence changes.

The monoamine oxidase B (MAO-B) gene was examined in 100 alleles derived from 80 Caucasian, 10 African-American, 5 Asian, and 5 Native American male patients with schizophrenia to identify sequence changes that might be associated with the disease. Approximately 235 kb of genomic sequence, primarily in coding regions, were screened by dideoxy fingerprinting, a modification of single-strand conformational polymorphism (SSCP) analysis that detects virtually 100% of sequence changes [Sarkar et al. (1992): Genomics 13:441-443; Liu and Sommer (1994): PCR Methods Appl 4:97-108]. No sequence changes of likely functional significance were identified, suggesting that mutations affecting the structure of the MAO-B protein are uncommon in the general population and are unlikely to contribute significantly to the genetic predisposition to schizophrenia. Eight polymorphisms were identified in African-Americans and Native Americans, but none were identified among Caucasians. Of the eight observed polymorphisms, a set of five transitions and one microdeletion was identified within approximately 17 kb of genomic sequence in the same 3 African-American individuals, while the remaining 7 African-Americans had a sequence identical to that in Caucasians. The presence of two such haplotypes, without intermediates, is compatible with the hypothesis that germline mutations can occur in clusters, as also suggested by other recent findings.

The D5 dopamine receptor gene in schizophrenia: identification of a nonsense change and multiple missense changes but lack of association with disease.

To determine whether mutations in the D5 dopamine receptor gene (DRD5) are associated with schizophrenia, the gene was examined in 78 unrelated schizophrenic individuals (156 DRD5 alleles). After amplification by the polymerase chain reaction, products were examined by dideoxy fingerprinting (ddF), a screening method related to single strand conformational polymorphism analysis that detects essentially 100% of mutations. All samples with abnormal ddF patterns were sequenced. Nine different sequence changes were identified. Five of these were sequence changes that would result in protein alterations; of these, one was a nonsense change (C335X), one was a missense change in an amino acid conserved in all dopamine receptors (N351D), two were missense changes in amino acids that are identical in only some dopamine receptors and in only some species (A269V; S453C), and one was a missense change in a non-conserved amino acid (P330Q). To investigate whether the nonsense change (C335X), predicted to prematurely truncate the receptor protein and result in a 50% diminution of functional protein, was associated with schizophrenia, other neuropsychiatric diseases, or specific neuropsychological, psychophysiological, or personality traits, both case-control and family analyses were performed. No statistically-significant associations were detected with schizophrenia or other neuropsychiatric disease. There also were no significant associations between any one measure of neuropsychological function. However, a post-hoc analysis of combined measures of frontal lobe function hinted that heterozygotes for C335X may have a vulnerability to mild impairment, but these findings must be interpreted with caution.(ABSTRACT TRUNCATED AT 250 WORDS)

The rates and patterns of deletions in the human factor IX gene.

Deletions are commonly observed in genes with either segments of highly homologous sequences or excessive gene length. However, in the factor IX gene and in most genes, deletions (of > or = 21 bp) are uncommon. We have analyzed DNA from 290 families with hemophilia B (203 independent mutations) and have found 12 deletions > 20 bp. Eleven of these are > 2 kb (range > 3-163 kb), and one is 1.1 kb. The junctions of the four deletions that are completely contained within the factor IX gene have been determined. A novel mutation occurred in patient HB128: the data suggest that a 26.8-kb deletion occurred between two segments of alternating purines and pyrimidines and that a 2.3-kb sense strand segment derived from the deleted region was inserted. For our sample of 203 independent mutations, we estimate the "baseline" rates of deletional mutation per base pair per generation as a function of size. The rate for large (> 2 kb) deletions is exceedingly low. For every mutational event in which a given base is at the junction of a large deletion, there are an estimated 58 microdeletions (< 20 bp) and 985 single-base substitutions at that base. Analysis of the nine reported deletion junctions in the factor IX gene literature reveals that (i) five are associated with inversions, orphan sequences, or sense strand insertions; (ii) four are simple deletions that display an excess of short direct repeats at their junctions; (iii) there is no dramatic clustering of junctions within the gene; and (iv) with the exception of alternating purines and pyrimidines, deletion junctions are not preferentially associated with repetitive DNA.

Dopamine D4 receptor variants in unrelated schizophrenic cases and controls.

The D4 dopamine receptor (D4DR) exists in multiple allelic forms (Van Tol et al.: Nature 358:149-152, 1992) which involve different numbers of a 48 basepair repeat sequence in the putative third cytoplasmic loop. Different binding properties have been reported for at least three of the alleles in cDNA binding assays with clozapine, an atypical neuroleptic, and spiperone (Van Tol et al., 1992). We have examined 115 unrelated schizophrenic cases defined by DSM-III-R criteria and 115 controls of similar ethnicity to determine the frequency of seven different D4 alleles in these groups. No statistically significant difference in the distribution of the alleles existed between cases and controls, although a trend towards a greater prevalence of homozygotes for the 4-repeat allele was observed in schizophrenics.