Nobuaki Wakamatsu

Mutations in SIP1 , encoding Smad interacting protein-1, cause a form of Hirschsprung disease

Hirschsprung disease (HSCR) is sometimes associated with a set of characteristics including mental retardation, microcephaly, and distinct facial features, but the gene mutated in this condition has not yet been identified. Here we report that mutations in SIP1, encoding Smad interacting protein-1, cause disease in a series of cases. SIP1 is located in the deleted segment at 2q22 from a patient with a de novo t(2;13)(q22;q22) translocation. SIP1 seems to have crucial roles in normal embryonic neural and neural crest development.

Missense and Nonsense Mutations in the Lysosomal α-Mannosidase Gene (MANB) in Severe and Mild Forms of α-Mannosidosis

Summary α-Mannosidosis is an autosomal recessive lysosomal-storage disorder caused by a deficiency of lysosomal α-mannosidase activity. This disease shows a wide range of clinical phenotypes, from a severe, infantile form (type I), which is fatal at

Late infantile Hirschsprung disease–mental retardation syndrome with a 3-bp deletion in ZFHX1B

A 48-year-old woman with late infantile onset mental retardation developed megacolon. Although the patient had no typical clinical features of Hirschsprung disease–mental retardation syndrome, a new 3–base pair deletion, eliminating an Asn, was identified in the responsible gene ZFHX1B. This suggests that screening for ZFHX1B mutations is warranted even in the absence of typical clinical features of the syndrome.

Two mutations remote from an exon/intron junction in the β-hexosaminidase β-subunit gene affect 3’-splice site selection and cause Sandhoff disease

Four unrelated Japanese patients with infantile Sandhoff disease (β-hexosaminidase β-subunit deficiency) have been studied for the molecular basis of their severe phenotype. Two patients had complex base substitutions; one patient was homoallelic for a triple mutation (P417L, K121R, and S255R) and the other was a compound heterozygote of a double (P417L and K121R) mutation and the triple mutation. K121R is known to be a functional polymorphism, while P417L (exon 11, +8 C→T) generates predominantly an abnormally spliced mRNA at base +112 of exon 11 and has been described in two patients with a juvenile form of the disease. The mild phenotype is attributed to the presence of a small amount of normally spliced mRNA. S255R is a novel mutation without prior description in the literature. An expression study of the normally spliced cDNA with the double and the triple mutations gave about 70% and 30% of normal activity, respectively. This finding suggests that S255R further reduces the catalytic activity of the already below-threshold amount of normally spliced mRNA and accounts for the more severe phenotype in our patients. In the other two patients, a novel disease-causing base transition was found within intron 10, away from the intron/exon junction (–17 a→g). This mutation caused abnormal 3’ splicing at position –37 of intron 10, and no normally spliced product was detectable upon RT-PCR analysis. We noted an unusually low splice site score (61.8) for the exon 10/intron 11 junction and suspected that this might be partially responsible for the aberrant splicing in these mutations. To test this hypothesis, we constructed four chimeric cDNAs all with an additional intron 10 inserted and evaluated their splicing efficiency. They, respectively, had the normal sequence, P417L (exon 11, +8 C→T), the intronic mutation (–17 a→g), and the intronic mutation with an artificially engineered intron 10/exon 11 junction of a higher splice site score (85.1). Of the total transcripts, 67% and 32% were correctly spliced in the normal chimeric construct and P417L, respectively, while no normally spliced product was generated either in the chimeric construct with –17 a→g or in that with a high splice site score. The sequence around the adenosine –17 residue upstream of the normal acceptor splice site in this report, UGCAAU (–21 to –16), matches the consensus branchpoint sequence YNYRAY (Y, pyrimidine; R, purine; N, any base) reported in the literature. The mutation in this study is most likely to abolish lariat formation because the artificial site of the high splice site score did not improve splicing efficiency.

Mutations producing premature termination of translation and an amino acid substitution in the sterol 27-hydroxylase gene cause cerebrotendinous xanthomatosis associated with parkinsonism.

OBJECTIVES Mutational analysis of the sterol 27-hydroxylase (CYP27) gene was performed on three patients from two Japanese families who had cerebrotendinous xanthomatosis (CTX) associated with parkinsonism. METHODS Clinical evaluations, brain MRI studies, and laboratory analyses were completed on the three patients. The CYP27 gene was analysed for mutations by PCR amplification of gene segments followed by direct sequencing. RESULTS Two different, homozygous mutations were identified in these families. One is a novel transition, substituting T for G at Glu162 (GAG) resulting in a stop codon (TAG). The other is also a transition, substituting T for C at Arg441 (CGG) resulting in Trp (TGG). The second is located in two amino acids ahead of the heme ligand binding site (Cys443) of the protein likely rendering it non-functional. It is the most common CTX mutation in Japanese patients. CONCLUSIONS CTX with parkinsonism is caused by mutations with a severe impact on enzyme function. The two mutations described here are likely to cause loss of function because they are chain terminating or affect an essential site in the protein.

Endogenous thiol protease inhibitor from rat liver

Abstract A thiol protease inhibitor was purified from rat liver by a rapid procedure involving heat treatment of the post-lysosomal fraction, affinity chromatography on papain-Sepharose 4B and Sephadex G-75. The purified inhibitor appeared homogeneous on sodium dodecyl sulfate electrophoresis. The inhibitor had a molecular weight of about 11,500 and consisted of three forms (pI 4.9, 5.2 and 5.6). The preparation inhibited thiol proteases, such as papain, cathepsin H, cathepsin B and cathepsin L, but not serine proteases (trypsin, chymotrypsin, mast cell protease and cathepsin A) or cathepsin D.

Characterization of the human MANB gene encoding lysosomal α -d-mannosidase

Abstract Genomic clones of human MANB gene encoding the lysosomal enzyme, α-mannosidase, have been isolated, sequenced and analyzed. The human MANB gene spans approximately 22xa0kb and consists of 24 exons. The 5′ flanking region of the gene shows a high G+C content and has two Sp1 and three AP-2 sites. Promoter analysis using deletion constructs of the 5′ flanking region fused to the bacterial CAT gene showed that 150xa0bp of 5′ sequence could drive the expression of MANB in COS 7 cells. Determination of the sequence of the 5′ end of the α-mannosidase mRNA by 5′ RACE protocol showed that transcription is initiated from a cluster of sites centered −28 and −20xa0bp from the first in-frame ATG. These data demonstrate that, like other lysosomal enzyme genes such as those for β-glucuronidase or β-hexosaminidase, the human MANB gene is controlled by a short 5′ flanking sequence located near the initiation codon.

NOVEL GENETIC MUTATIONS RESPONSIBLE FOR THE HPRT DEFICIENCY AND THE CLINICAL PHENOTYPES IN JAPANESE

We have identified six novel mutations in Japanese families of HPRT deficiency manifesting different clinical phenotypes. A missense mutation (Y195C) was identified in a patient with hyperuricemia and gout (Case 1). In Cases 2 and 3 with mild neurological symptoms, missense mutations L147P and K159E were detected, respectively. A point mutation 532+2T>C causing splicing error was found in a severe form of partial HPRT deficiency (Case 4). Two mutations causing splicing error, 609+1delGT (Case 5) and 610-−1G>A (Case 6), resulted in the classic Lesch-Nyhan syndrome.

Modification of rat liver fructose biphosphate aldolase by lysosomal proteinases

In vivo proteolytic modification of liver aldolase on administration of leupeptin, a thiol proteinase inhibitor of microbial origin, is reported. When leupeptin was injected into rats, the activity of aldolase in the liver decreased to 40% of that in control rats. Molecular properties of aldolase isolated from the livers of control rats and leupeptin-treated rats indicated that a decrease of aldolase activity is attributable to hydrolysis of a peptide linkage(s) near the carboxyterminal of the enzyme. Injection of leupeptin also caused marked increase in the activities of free lysosomal proteinases, such as cathepsin A and cathepsin D and moderate increase of cathepsin B and cathepsin L. Increase in free activity of cathepsin A returned to the level of control rats by 12 hr after injection of leupeptin, whereas 36 hr was required for recovery of decreased aldolase activity. When insulin was coinjected with leupeptin, increase in the activity of free cathepsin A and decrease of activity of aldolase produced by the injection of leupeptin was prevented. These findings indicate that modification of aldolase may be due to action of a lysosomal protease(s). Incubation of the purified aldolase with the lysosomal fraction produced the same changes in properties of aldolase as those observed in vivo on injection of leupeptin. The aldolase inactivating proteinase in the lysosomal fraction was inhibited by PMSF and leupeptin and not by pepstatin. Purified cathepsin A (a serine proteinase), cathepsin B and cathepsin L (thiol proteinase) are potent inactivators of aldolase but cathepsin H and cathepsin D are not. Cathepsin A, B and L are involved in inactivation of aldolase in lysosomes. Endogenous thiol proteinase inhibitor which inhibits lysosomal thiol proteinases (cathepsin B, L and H) is found in the cytosol fraction of liver. The level of thiol proteinase inhibitor actually decreased to 60% of that in control rats in leupeptin-treated rats, suggesting that non-thiol proteinase cathepsin A is a major factor in inactivation of aldolase in lysosomes. Not only leupeptin but also other proteinase inhibitors (antipain, E-64-D, chloroquine) caused increase of labilization of the lysosomes and decrease in aldolase activity. Physiological stimuli which are known to induce the labilization of the lysosomal membrane, such as starvation and glucagon, caused slight or no significant increase of activities of free cathepsin A and D and resulted in no apparent change in aldolase activity.

A Rare Case of Complete Human Erythrocyte AMP Deaminase Deficiency Due to Two Novel Missense Mutations in AMPD3

Human erythrocyte AMP deaminase (AMPD3) deficiency is a clinically asymptomatic condition characterized by a 50% increase in steady‐state levels of ATP in affected cells. The deficiency in Japanese is associated 75% of the time with the same mutation of R573C, and 25% of the time with other heterogeneous mutations of the AMPD3 gene. The heterozygote frequency was estimated at about 1/30. We previously reported five Japanese individuals who had a complete deficiency of AMPD3. Four were homozygotes for the major mutation of R573C; however, one female did not have the R573C allele. To clarify the mutations in her AMPD3 gene, we analyzed the AMPD3 gene and detected a minor mutation, W450R, derived from the mother and a novel mutation,Q712P, derived from the father. The expression study using AMPD3 cDNA containing both mutations showed that each mutation completely reduced the enzyme activity of AMPD3. As the frequency of carriers heterozygous for these mutations seems to be very low, identifying them may lead to a better understanding of the genetic background of populations in Japan.