Naoki Hamajima

A novel gene family defined by human dihydropyrimidinase and three related proteins with differential tissue distribution

We have isolated cDNA clones encoding dihydropyrimidinase (DHPase) from human liver and its three homologues from human fetal brain. The deduced amino acid (aa) sequence of human DHPase showed 90% identity with that of rat DHPase, and the three homologues showed 57-59% aa identity with human DHPase, and 74-77% aa identity with each other. We tentatively termed these homologues human DHPase related protein (DRP)-1, DRP-2 and DRP-3. Human DRP-2 showed 98% aa identity with chicken CRMP-62 (collapsin response mediator protein of relative molecular mass of 62 kDa) which is involved in neuronal growth cone collapse. Human DRP-3 showed 94-100% aa identity with two partial peptide sequences of rat TOAD-64 (turned on after division, 64 kDa) which is specifically expressed in postmitotic neurons. Human DHPase and DRPs showed a lower degree of aa sequence identity with Bacillus stearothermophilus hydantoinase (39-42%) and Caenorhabditis elegans unc-33 (32-34%). Thus we describe a novel gene family which displays differential tissue distribution: i.e., human DHPase, in liver and kidney; human DRP-1, in brain; human DRP-2, ubiquitously expressed except for liver; human DRP-3, mainly in heart and skeletal muscle.

Population and family studies of dihydropyrimidinuria: Prevalence, inheritance mode, and risk of fluorouracil toxicity

To evaluate the prevalence of dihydropyrimidinuria (DHPuria), we analyzed urine samples from 21,200 healthy Japanese infants, and found two cases of DHPuria without clinical symptoms. Based on this result, we estimated the prevalence to be approximately 1/10,000 births in Japan. In addition, we analyzed pyrimidine catabolism on a previously reported family with an adult DHPuria case. We newly identified the sister of the propositus as the second case of DHPuria in this family, because she excreted large amounts of dihydrouracil and dihydrothymine. The parents and the child of the propositus showed slight increases of dihydrouracil and dihydrothymine. This is the first family with 2 cases of DHPuria, indicating that DHPuria is an inherited condition. To determine the inheritance of DHPuria in this family and to examine the risk of 5-fluorouracil (5-FU) toxicity, a uracil loading test was performed on the parents. Urinary dihydrouracil concentrations in the parents after the loading were several times higher than those in normal control persons, the finding being consistent with DHPuria heterozygotes. This, along with data on the propositus, his sister, and his child, indicates that DHPuria is an autosomal recessive condition. In addition, DHPuria homozygotes may have a high risk of 5-FU toxicity, while the risk is relatively low in heterozygotes.

Dihydropyrimidinase deficiency : structural organization, chromosomal localization, and mutation analysis of the human dihydropyrimidinase gene

Dihydropyrimidinase (DHP) deficiency (MIM 222748) is characterized by dihydropyrimidinuria and is associated with a variable clinical phenotype. This disease might be associated with a risk of 5-fluorouracil toxicity, although no cases have been reported. We present here both the molecular characterization of the human DHP gene and, for the first time, the mutations causing DHP deficiency. The human DHP gene spans >80 kb and consists of 10 exons. It has been assigned to 8q22, by FISH. We performed mutation analysis of genomic DNA in one symptomatic and five asymptomatic individuals presenting with dihydropyrimidinuria. We identified one frameshift mutation and five missense mutations. Two related Japanese adult subjects were homozygous for the Q334R substitution, whereas two other, unrelated Japanese infant subjects were heterozygous for the same mutation, but this mutation is not common in the Japanese population. A Caucasian pediatric patient exhibiting epileptic attacks, dysmorphic features, and severe developmental delay was homozygous for W360R. Using a eukaryotic expression system, we showed that all mutations reduced enzyme activity significantly, indicating that these are crucial DHP deficiency-causing mutations. There was no significant difference, in residual activity, between mutations observed in the symptomatic and those observed in the asymptomatic individuals.

Post-meiotic expression of the mouse dihydropyrimidinase-related protein 3 (DRP-3) gene during spermiogenesis

The dihydropyrimidinase‐related protein (DRP) family, originally identified in humans by their homology to dihydropyrimidinase, contains at least four members. Genes of this family, and their counterparts in other mammals and chickens, are expressed mainly in fetal and neonatal brain, suggesting that the encoded proteins have a physiological role in the development of the central nervous system. In addition, the DRP‐3 gene is expressed in testis as a shorter mRNA than the brain form. As a first step in understanding the extra‐neuronal function of DRP‐3, the structure and expression of testis DRP‐3 were examined. Testis DRP‐3 cDNA showed the same sequence as brain DRP‐3 cDNA, except for the 5′‐terminal end, which encodes a 5′‐untranslated region and the 11 N‐terminal amino acid residues, indicating that the two forms of DRP‐3 mRNA were transcribed from a single copy gene. Northern blotting analysis detected DRP‐3 mRNA in 30‐, 40‐ and 70‐day‐old, but not in 10‐ and 20‐day‐old testes. In situ hybridization analysis indicated that the expression of DRP‐3 in testis is restricted to post‐meiotic round spermatids. This is the first report of the expression of DRP genes in extra‐neuronal cells. Mol. Reprod. Dev. 51:105–111, 1998.

Molecular cloning and sequencing of a cDNA encoding dihydropyrimidinase from the rat liver

A cDNA encoding dihydropyrimidinase has been isolated from a rat cDNA library. The N-terminal and an internal amino acid sequences were determined, and PCR primers were designed based on these sequences. Using a cDNA fragment amplified by RT-PCR with these primers, three cDNA clones were isolated from a rat liver library. The clone with the longest insert of 2129 bp contained a 1557 bp open reading frame encoding a polypeptide of 519 residues with a molecular mass of 56,832 Da.

Increased protein stability of CDKN1C causes a gain-of-function phenotype in patients with IMAGe syndrome.

Mutations in the proliferating cell nuclear antigen (PCNA)-binding domain of the CDKN1C gene were recently identified in patients with IMAGe syndrome. However, loss of PCNA binding and suppression of CDKN1C monoubiquitination by IMAGe-associated mutations hardly explain the reduced-growth phenotype characteristic of IMAGe syndrome. We demonstrate here that IMAGe-associated mutations in the CDKN1C gene dramatically increased the protein stability. We identified a novel heterozygous mutation, c.815T>G (p.Ile272Ser), in the CDKN1C gene in three siblings manifesting clinical symptoms associated with IMAGe syndrome and their mother (unaffected carrier). PCNA binding to CDKN1C was disrupted in the case of p.Ile272Ser, and for two other IMAGe-associated mutations, p.Asp274Asn and p.Phe276Val. Intriguingly, the IMAGe-associated mutant CDKN1C proteins were fairly stable even in the presence of cycloheximide, whereas the wild-type protein was almost completely degraded via the proteasome pathway, as shown by the lack of degradation with addition of a proteasome inhibitor, MG132. These results thus suggested that the reduced-growth phenotype of IMAGe syndrome derives from CDKN1C gain-of-function due to IMAGe-associated mutations driving increased protein stability.

Differential expression of dihydropyrimidinase-related protein genes in developing and adult enteric nervous system

Abstract Dihydropyrimidinase-related proteins (DRPs) are involved in axonal outgrowth and pathfinding. However, little is known about their significance in the enteric nervous system (ENS), the largest and most complex division of the peripheral nervous system. Using in situ hybridization (ISH) and northern blotting, we examined mRNA expression of DRP-1–4 transcripts in the developing and adult mouse digestive tract and in the adult human colon. ISH detected the mouse DRP-3 transcript in the developing ENS on embryonic day (E)12 and at the later stages as well as in the adult intestine. Mouse DRP-1 and -2 transcripts appeared at E14. DRP-2 transcript was also detected in the adult intestine although DRP-1 expression was lower in the adult. DRP-4 gene was not expressed in the ENS during development or adulthood whereas the signal was apparent in the developing and adult central nervous system (CNS). The DRP expression pattern in the human colon was similar to that of the mouse large intestine. Northern blot analysis showed that DRPs were differentially expressed in the mouse and human intestines, supporting the results of ISH. These data suggest that DRPs play a role not only in the CNS but also in the ENS.

Cloning and characterization of the Caenorhabditis elegans CeCRMP/DHP-1 and -2; common ancestors of CRMP and dihydropyrimidinase?

The vertebrate CRMP (collapsin-response-mediator protein) gene family comprises at least four members. These CRMPs exhibit about 60% amino acid identity with vertebrate dihydropyrimidinase (DHP), an amidohydrolase involved in the pyrimidine degradation pathway. CRMP is also referred to as DRP (DHP-related protein), TOAD-64 (turned on after division, 64 kDa) and Ulip (Unc-33-like phosphoprotein). These vertebrate CRMPs are expressed mainly in early neuronal differentiation, which suggests that they play a role in neuronal development. In this study we isolated two cDNA clones from nematode C. elegans based on their sequence homology to vertebrate CRMPs and DHP. These two molecules, termed CeCRMP/DHP-1 and -2, turned out to be Ulip-B and -A, respectively, which were previously identified in the C. elegans genomic database by Byk et al. (1998). These newly isolated molecules were believed to represent a common ancestral state before the gene duplication between CRMPs and DHP. CeCRMP/DHP-1 and -2 protein retained all putative zinc-binding residues thought to be essential for the amidohydrolase activity of DHP and exhibited a weak amidohydrolase activity when 5-bromo-dihydrouracil was used as a substrate. Whole-mount in situ hybridization and expression analysis using GFP fusions revealed that CeCRMP/DHP-1 was transiently expressed in the hypodermis of C. elegans during the early larva stage. CeCRMP/DHP-1 was also expressed in a single nerve cell between the pharynx and ring neuropil. On the other hand, expression of CeCRMP/DHP-2 was observed in the body wall muscle throughout the lifespan of C. elegans. These results indicate that a major site of CeCRMP/DHP-1 and -2 expression is non-neuronal. Targeted gene disruption of CeCRMP/DHP-2 caused no particular difference in appearance or movement phenotype.

A case of Guillain–Barré syndrome with meningeal irritation

Here, we report a 5-year-old girl with Guillain-Barré syndrome who presented with a chief complaint of pain in the extremities, which was followed by neck stiffness. Bladder dysfunction was found, which required catheterization. Magnetic resonance imaging revealed marked enhancement of the nerve roots in the cauda equina on T1-weighted imaging after gadolinium injection, and nerve conduction studies led to a diagnosis of Guillain-Barré syndrome. Her symptoms improved after intravenous immunoglobulin therapy, but her neck stiffness remained 16 days after admission. Four weeks after admission, she could walk without support. As patients with signs of meningeal irritation may be diagnosed with other diseases, such as meningitis, it is important to recognize atypical cases of pediatric Guillain-Barré syndrome to achieve early diagnosis and treatment.

Reply to the letter: A case of Guillain–Barré syndrome with meningeal irritation

We thank Dr. Rebai and colleagues for their interest in our case report ‘‘A case of Guillain–Barré syndrome with meningeal irritation” [1]. They presented a 2-yearold girl diagnosed with Guillain–Barré syndrome (GBS) and presenting with an extremely painful stiff neck with retrocollis, tetraparesis, and generalized areflexia on neurological examination. In their case, enhancement of the medullary cone and cauda equine was revealed by gadolinium images, and the cerebrospinal fluid was high in protein and had a normal cell count, which were compatible with GBS. Although atypical signs of GBS, such as meningeal irritation, have been reported [2,3], a case of GBS with meningeal irritation might be suspected to be bacterial meningitis at first, such as in our case. Neck stiffness is uncommon in GBS in the pediatric population, despite previous reports of it being present in 16 of 46 cases [4], as well as in 38% of children aged <6 years old [5] who were diagnosed with GBS with accompanying neck stiffness. For early diagnosis and treatment, case reports of GBS with neck stiffness, such as that by Dr. Rebai and our report, might be important.