Beginning with three partial cDNA clones of the RNA genome of human hepatitis delta virus (HDV), we assembled the complete 1,679-base sequence on a single molecule and then inserted a trimer of this into plasmid pSVL, a simian virus 40-based eucaryotic expression vector. This construct was used to transfect both monkey kidney (COS7) and human hepatocellular carcinoma (HuH7) cell lines. In this way we obtained replication of the HDV RNA genome and the appearance, in the nucleoli, of the delta antigen, the only known virus-coded protein. This proved both that the HDV genome could replicate in nonliver as well as liver cells and that there was no requirement for the presence of hepatitis B virus sequences or proteins. When the pSVL construct was made with a dimer of an HDV sequence with a 2-base-pair deletion in the open reading frame, genome replication was reduced at least 40-fold. However, when we cotransfected with a plasmid that expressed the correct delta antigen, the mutated dimer achieved a level of genome replication comparable to that of the nonmutated sequence. We thus conclude that the delta antigen can act in trans and is essential for replication of the HDV genome.

Previous studies on the incidence of the various types of mucopolysaccharidoses (MPS) in different populations have shown considerable variation. However, information regarding the incidence of MPS in the Asian population is lacking. An epidemiological study of the MPS disorders in Taiwan using multiple ascertainment sources was undertaken, and incidences of different types of MPS during the period of 1984-2004 were estimated. We compared our data with previous reports in different populations. The combined birth incidence for all MPS cases was 2.04 per 100,000 live births. MPS II (Hunter syndrome) had the highest calculated birth incidence of 1.07 per 100,000 live births (2.05 per 100,000 male live births), comprising 52% of all MPS cases diagnosed. The birth incidences of MPS I (Hurler syndrome), III (Sanfilippo syndrome), IV (Morquio syndrome), and VI (Maroteaux-Lamy syndrome) were 0.11, 0.39, 0.33, and 0.14 per 100,000 live births, respectively, which accounted for 6%, 19%, 16%, and 7% of all MPS, respectively. No cases of MPS III D (Sanfilippo syndrome type D), MPS IV B (Morquio syndrome type B), MPS VII (Sly syndrome) or MPS IX were ascertained during the study period. Overall incidence of MPS in Taiwan was consistent with that reported in Western populations. However, in contrast to the higher incidence of MPS I in most Western populations, this study showed a higher incidence of MPS II in Taiwan. It remains to be investigated whether this discrepancy is attributed to the under-diagnosis of MPS I in Taiwan or to ethnic differences.

The replication of the RNA genome of hepatitis delta virus is greatly facilitated by the presence of the only known virus-coded protein, the delta antigen. Most, if not all, infections are characterized by the presence of two electrophoretic forms of the delta antigen. These forms correspond to polypeptide lengths of 195 and 214 amino acids which are encoded by genomes with different nucleotide sequences. We used cDNA transfections to investigate the functions of these two forms of the delta antigen. We found that only the small form of delta antigen supported hepatitis delta virus genome replication and that the large form acted as a dominant negative repressor of such replication. This inhibition was potent. For example, the amount of genome replication was reduced eightfold when as little as 10% of the delta antigen was present as the large form. One interpretation of our results is that the delta antigen normally functions as part of a multimeric structure. In addition, our data suggest that synthesis of the large form, either during genome replication in cultured cells or even during infection in animals, may suppress delta replication, possibly leading to a self-limiting infection.

Three independent lines of evidence showed that when an infectious clone of hepatitis delta virus of known sequence was used to initiate genome replication, up to 41% of the genomes were specifically mutated in the amber termination codon (UAG to UGG) for the open reading frame of the delta antigen, thereby increasing the length of the predicted protein from 195 to 214 amino acids. This change was detected only on molecules that participated in RNA-directed RNA synthesis.

Hepatitis delta antigen (HIAg) is an RNA-binding protein with binding specificity for hepatitis delta virus (HDV) RNA (J.