Nobumasa Inoue

PIG-B, a membrane protein of the endoplasmic reticulum with a large lumenal domain, is involved in transferring the third mannose of the GPI anchor.

Many eukaryotic cell surface proteins are bound to the membrane via the glycosylphosphatidylinositol (GPI) anchor that is covalently linked to their carboxy‐terminus. The GPI anchor precursor is synthesized in the endoplasmic reticulum (ER) and post‐translationally linked to protein. We cloned a human gene termed PIG‐B (phosphatidylinositol glycan of complementation class B) that is involved in transferring the third mannose. PIG‐B encodes a 554 amino acid, ER transmembrane protein with an amino‐terminal portion of approximately 60 amino acids on the cytoplasmic side and a large carboxy‐terminal portion of 470 amino acids within the ER lumen. A mutant PIG‐B lacking the cytoplasmic portion remains active, indicating that the functional site of PIG‐B resides on the lumenal side of the ER membrane. The PIG‐B gene was localized to chromosome 15 at q21‐q22. This autosomal location would explain why PIG‐B is not involved in the defective GPI anchor synthesis in paroxysmal nocturnal hemoglobinuria, which is always caused by a somatic mutation of the X‐linked PIG‐A gene.

Pregnancy-induced thrombocytopenia and TTP, and the risk of fetal death, in Upshaw-Schulman syndrome: a series of 15 pregnancies in 9 genotyped patients

Upshaw–Schulman syndrome (USS) is a congenital thrombotic thrombocytopenic purpura (TTP) due to mutations in the gene that encodes for ADAMTS13 (ADAMTS13), but its clinical signs may be mild or absent during childhood. We have identified 37 patients with USS (24 females, 13 males) belonging to 32 families. The nine women from six families who were diagnosed during their first pregnancy are the focus of this report. Six of the nine women had episodes of thrombocytopenia during childhood misdiagnosed as idiopathic thrombocytopenic purpura. Thrombocytopenia occurred during the second–third trimesters in each of their 15 pregnancies, with 16 babies (one twin pregnancy), often followed by TTP. Of 15 pregnancies, eight babies were stillborn or died soon after birth, and the remaining seven were all premature except one, who was born naturally following plasma infusions to the mother that had started at 8 weeks’ gestation. All nine USS women had severely deficient ADAMTS13 activity. ADAMTS13 analyses demonstrated that eight women were compound heterozygotes of Y304C/G525D (2 siblings), R125VfsX6/Q1302X (2 siblings), R193W/R349C (2 siblings), I178T/Q929X, and R193W/A606P; one woman was homozygous for R193W. Only the R193W mutation has been previously reported. These observations emphasize the importance of measuring ADAMTS13 activity in the evaluation of thrombocytopenia during childhood and pregnancy.

Human and mouse GPAA1 (Glycosylphosphatidylinositol anchor attachment 1) genes: genomic structures, chromosome loci and the presence of a minor class intron

Many eukaryotic cell surface proteins are anchored to the membrane with glycosylphosphatidylinositol (GPI) that is covalently linked to the carboxyl-terminus. A Saccharomyces cerevisiae gaa1 mutant is defective in posttranslational attachment of GPI to proteins. A recent report demonstrated that the GPAA1 gene encodes a component of a transamidase that mediates GPI-anchor attachment. Here, we report structures and chromosome loci of human and mouse GPAA1 genes. Both genes consist of twelve exons that span about 4 kb. Human and mouse GPAA1s are located at 8q24.3 and 15E, respectively. There is a human pseudo GPAA1 gene (GPAA1P1) that is located at 2q12→q14. Introns 8 of human and mouse GPAA1s were minor class introns bearing AT at the 5′ splice sites and AC and AT at the 3′ splice sites, respectively. The 3′ splice sites of corresponding introns of African green monkey, Chinese hamster, dog and rat were AC, AT, AT and AA, respectively. The mouse GPAA1 gene (Gpaa1) bearing AG at the 3′ splice site prepared by site-directed mutagenesis was functional, indicating that any nucleotide is allowed at the 3′ end of a minor class intron.

Assignment1 of Microrchidia (Morc) to mouse chromosome 16 by interspecific backcross linkage analysis and human chromosome 3q13 using somatic cell hybrids and in situ hybridization

Morc is a novel gene discovered by positional cloning efforts whose functional abrogation results in arrest of mouse germ cell development (Watson et al., 1998). However, the mechanism by which germ cell growth is arrested is unknown at present. Mouse MORC, a 950-residue protein, defines a new family of proteins that share extensive homology and are conserved at least to C. elegans (Inoue et al., 1999). Human MORC encodes a protein of 984 amino acids that is 66% identical to mouse MORC. Mutations in human MORC could cause male infertility, and abnormal MORC expression might be germane to testicular germ cell tumors. Interestingly, all members of this family contain a conserved domain that may confer ATPase activity. We have mapped mouse Morc to both identify possible cosegregation with previously defined mouse mutants and to define Morc’s relationship with human homology groups, and in parallel we have mapped human MORC in order to gain insight into its possible roles in human clinical disorders. Mouse Morc maps to mouse chromosome 16 between Gap43 and Aprt2. Human MORC maps to human chromosome 3q13. These results are consistent with other human/mouse homology relationships (DeBry and Seldin, 1996). Materials and methods

Unsuppressed serum albumin levels may jeopardize the clinical relevance of the international staging system to patients with light chain myeloma

The international staging system (ISS) is the most commonly used risk‐stratification system for patients with multiple myeloma (MM) and is determined by serum albumin and β2‐microglobulin levels. In the two determinants, β2‐microglobulin levels are frequently observed to be elevated in patients with myeloma, particularly in those with renal impairment. In comparison with patients with intact immunoglobulin myeloma, patients with LC myeloma do not necessarily show decreased levels of serum albumin. The clinical impact of ISS in patients with LCMM, in particular the distinction between ISS I and II, may be complicated due to non‐decreased levels of serum albumin in both stages. Accordingly, we have attempted to assess clinical relevance of the ISS in patients with LC myeloma. The clinical data of 1899 patients with MM diagnosed between January 2001 and December 2012 were collected from 38 affiliated hospitals of the Japanese Society of Myeloma. Significant difference was not found between stage I (n = 72) and stage II (n = 92) in LC myeloma patients (n = 307). The mean serum albumin concentration of patients with LC myeloma was within the reference range but higher than that of patients with IgG + IgA myeloma (n = 1501), which complicates the distinction between ISS stage I and II myeloma. Patients with LC myeloma had low frequencies of t(4; 14) and high frequency of elevated lactate dehydrogenase, and despite a relevant amount of missing data in our registry (R‐ISS stage I; n = 11, stage II; n = 32, and stage III: n = 18), the information included in the R‐ISS scoring system seems to be more accurate than ISS to obtain a reliable risk stratification approach in non‐ISS stage III LC myeloma patients.

Phase II study of intensified rituximab induction and maintenance for low grade B cell lymphoma

Abstract Rituximab has markedly improved the outcomes of B cell lymphoma, and its maintenance has been shown to be beneficial in low grade B cell lymphoma (LGBCL). We conducted a multicenter, phase II trial of intensive rituximab induction and maintenance therapy for LGBCL to optimize the rituximab monotherapy. Patients with newly diagnosed or rituximab naïve relapsed LGBCL received 8 weekly rituximab as induction, then continued maintenance therapy with rituximab for 4 weeks at 6-month intervals. The primary endpoint was the overall response rate (ORR). Forty-five patients were enrolled from 2005 to 2009 and 36 were eligible. The ORR was 83.3% (30/36) with a complete response rate of 72.2% (26/36). The 3-year progression-free survival (PFS) was 76.7% with a median follow-up of 43.0 months. Five grade three toxicities were observed (no grade 4). Our findings suggest that this regimen demonstrates high activity with durable PFS and minimal toxicity in LGBCL patients.