PubMed Health⌕ Search

Biomedical subjects

H C Chi

Publications and source records attributed to H C Chi.

12 recordsLinked to original sources
PubMed2005

Dopamine receptor D4 (DRD4) gene in Han Chinese children with attention-deficit/hyperactivity disorder (ADHD): increased prevalence of the 2-repeat allele.

There is an increased prevalence of the 7-repeat (7R) allele of the dopamine receptor D4 (DRD4) gene in attention-deficit/hyperactivity disorder (ADHD). However, the population prevalence of the 7R allele varies considerably across ethnicity and is very low in Asians. To test whether this 7R allele/ADHD association still held in a Chinese clinical sample, 32 Han Chinese children with a confirmed ADHD diagnosis and normal IQ who were methylphenidate-responders were genotyped. None of them had a DRD4 7R allele. Instead, we observed a significantly increased prevalence of the 2-repeat (2R) allele in this clinical sample (33%) compared to ethnically-matched controls (20%) (chi(2)(1d.f.) = 5.90, P = 0.015). This approximately 1.65-fold increase of the 2R allele in our probands is close to the observed increase of the 7R allele in European-ancestry ADHD children. Recent genetic studies have indicated that the 2R allele in Asians is likely derived from the 7R allele. Further, available biochemical data indicate that both the 2R and 7R protein have blunted responses to dopamine compared to the 4R protein. Based on these results, we propose that the observed increased prevalence of the 2R allele in our Han Chinese ADHD probands is still consistent with the 7R allele hypothesis of ADHD in European-ancestry children. Recent studies have suggested that any variant from the conserved ancestral 4R allele might potentially alter biochemistry/phenotype. We hypothesize that an increased frequency of any non-4R allele may define the association of the DRD4 gene with ADHD that holds across ethnicity. The present findings, however, obtained with a small ADHD sample size, should be replicated.

Adolescent↗
PubMed2001

A sequence-ready map of the human chromosome 1q telomere.

A 260-kb half-YAC clone derived from human chromosome 1q was mapped at high resolution using cosmid subclone fingerprint analysis and was integrated with overlapping clones from the telomeric end of a separately derived 1q44 BAC contig to create a sequence-ready map extending to the molecular telomere of 1q. Analysis of 100 kb of sample sequences from across the 260-kb region encompassed by the half-YAC revealed the presence of EST sequence matches corresponding to 12 separate Unigene clusters and to 12 separate unclustered EST sequences. Low-copy subtelomeric repeats typical of many human telomere regions are present within the distal-most 30 kb of 1q. The previously isolated and radiation hybrid-mapped markers Bda84F03, 1QTEL019, and WI11861 localized at distances approximately 32, 88, and 99 kb, respectively, from the 1q terminus. This sequence-ready map permits high-resolution integration of genetic maps with the DNA sequences directly adjacent to the tip of human chromosome 1q and will enable telomeric closure of the human chromosome 1q DNA reference sequence by connecting the molecular 1q telomere to an internal BAC contig.

Chromosomes, Artificial, Bacterial↗
PubMed2001

Integration of telomere sequences with the draft human genome sequence.

Telomeres are the ends of linear eukaryotic chromosomes. To ensure that no large stretches of uncharacterized DNA remain between the ends of the human working draft sequence and the ends of each chromosome, we would need to connect the sequences of the telomeres to the working draft sequence. But telomeres have an unusual DNA sequence composition and organization that makes them particularly difficult to isolate and analyse. Here we use specialized linear yeast artificial chromosome clones, each carrying a large telomere-terminal fragment of human DNA, to integrate most human telomeres with the working draft sequence. Subtelomeric sequence structure appears to vary widely, mainly as a result of large differences in subtelomeric repeat sequence abundance and organization at individual telomeres. Many subtelomeric regions appear to be gene-rich, matching both known and unknown expressed genes. This indicates that human subtelomeric regions are not simply buffers of nonfunctional 'junk DNA' next to the molecular telomere, but are instead functional parts of the expressed genome.

Chromosomes, Artificial, Bacterial↗
PubMed2000

Population structure and history in East Asia.

Archaeological, anatomical, linguistic, and genetic data have suggested that there is an old and significant boundary between the populations of north and south China. We use three human genetic marker systems and one human-carried virus to examine the north/south distinction. We find no support for a major north/south division in these markers; rather, the marker patterns suggest simple isolation by distance.

China↗
PubMed2000

Attention deficit/hyperactivity disorder children with a 7-repeat allele of the dopamine receptor D4 gene have extreme behavior but normal performance on critical neuropsychological tests of attention.

An association of the dopamine receptor D4 (DRD4) gene located on chromosome 11p15.5 and attention deficit/hyperactivity disorder (ADHD) has been demonstrated and replicated by multiple investigators. A specific allele [the 7-repeat of a 48-bp variable number of tandem repeats (VNTR) in exon 3] has been proposed as an etiological factor in attentional deficits manifested in some children diagnosed with this disorder. In the current study, we evaluated ADHD subgroups defined by the presence or absence of the 7-repeat allele of the DRD4 gene, using neuropsychological tests with reaction time measures designed to probe attentional networks with neuroanatomical foci in D4-rich brain regions. Despite the same severity of symptoms on parent and teacher ratings for the ADHD subgroups, the average reaction times of the 7-present subgroup showed normal speed and variability of response whereas the average reaction times of the 7-absent subgroup showed the expected abnormalities (slow and variable responses). This was opposite the primary prediction of the study. The 7-present subgroup seemed to be free of some of the neuropsychological abnormalities thought to characterize ADHD.

Alleles↗
PubMed1999

Genetic analysis of West Nile New York 1999 encephalitis virus.

Analysis of the genome of the flavivirus responsible for the 1999 New York City encephalitis epidemic cloned from human brain by reverse-transcription polymerase chain reaction Indicates its identity as a lineage I West Nile virus (WNV; WNV-NY1999) closely related to WNVs previously isolated In the Middle East.

Amino Acid Sequence↗
PubMed1995

An integrated physical map of human chromosome 16.

We describe an integrated physical, genetic and cytogenetic map of human chromosome 16 comprising both a low-resolution megaYAC map and a high-resolution cosmid contig/miniYAC map, which provides nearly complete coverage of the euchromatic arms of the chromosome. The physical map is anchored to a high-resolution cytogenetic breakpoint map and is integrated with genetic and gene transcript maps of the chromosome by sequence-tagged sites and clone hybridizations.

Animals↗
PubMed1989

Primary structure of the Drosophila laminin B2 chain and comparison with human, mouse, and Drosophila laminin B1 and B2 chains.

Laminin, a major component of basement membranes, is a large glycoprotein consisting of three disulfide-bonded subunits, A, B1, and B2. We have isolated and sequenced a Drosophila laminin B2 chain cDNA clone that spans 5737 nucleotides. The deduced amino acid sequence predicts that the mature and nonglycosylated polypeptide has a chain length of 1606 residues (Mr = 178,665). This B2 chain contains 100 half-cystine residues, most of which are located in two cysteine-rich domains, and 11 N-X-S or N-X-T sequences which are potential sites of N-linked glycosylation. The predicted secondary structure reveals the presence of six structurally distinct domains, of which two are mainly alpha-helical, two are cysteine-rich with homologous repeats, and two are globular regions. The Drosophila B2 chain is 40.3 and 41.1% identical to the human and mouse B2 chains, respectively, and 29.6, 30.0, and 29.4% identical to the Drosophila, human, and mouse B1 chains, respectively.

Amino Acid Sequence↗
PubMedDate not supplied

Structure of the Drosophila gene for the laminin B2 chain.

We isolated and sequenced a Drosophila genomic DNA sequence that encodes the entire coding region of the laminin B2 chain. The 11,464-bp genomic sequence contains a 2.1-kb of 5'-flanking DNA, ten exons, nine introns, and the 3'-flanking region. The first exon encodes a 5' untranslated region; the ATG translational start codon is in exon 2. The entire translated region is within a 8.3-kb Eco RI fragment. The Drosophila laminin B2 gene differs substantially in size and exon pattern from those of the human B1 and B2 genes. However, as in the case of the human B1 gene, the overall exon pattern of the Drosophila B2 gene does not correlate well with the highly conserved structural domains and internal repeats of the B2 polypeptide chain. Unlike the human and mouse B1 and B2 genes, the 2.1-kb 5'-flanking region of the Drosophila B2 gene contains a TATA box and two CAAT boxes. Other potential transcriptional regulatory sequences include two reverse complementary cAMP response element sequences; two sequences that are homologous to the retinoic acid response element motifs of the mouse B1 gene; and sequences homologous to the binding sites for transcription factors dFRA and dJRA, zeste, and possibly GAGA. When transfected into Drosophila SL-2 cells, pCAT plasmid containing 2,090 bp of 5'-flanking region shows a 3.0- to 3.5-fold increase in chloramphenicol acetyltransferase activity after induction with retinoic acid and/or 8-bromo-cAMP. These results suggest that this 5'-flanking promoter region may contain DNA sequences that can regulate the expression of the laminin B2 gene.

Amino Acid Sequence↗