Spectrum of mutations in the OCRL1 gene in the Lowe oculocerebrorenal syndrome

The oculocerebrorenal syndrome of Lowe (OCRL) is a multisystem disorder characterized by congenital cataracts, mental retardation, and renal Fanconi syndrome. The OCRL1 gene, which, when mutated, is responsible for OCRL, encodes a 105-kD Golgi protein with phosphatidylinositol (4,5)bisphosphate (PtdIn[4,5]P2) 5-phosphatase activity. We have examined the OCRL1 gene in 12 independent patients with OCRL and have found 11 different mutations. Six were nonsense mutations, and one a deletion of one or two nucleotides that leads to frameshift and premature termination. In one, a 1.2-kb genomic deletion of exon 14 was identified. In four others, missense mutations or the deletion of a single codon were found to involve amino acid residues known to be highly conserved among proteins with PtdIns(4,5)P2 5-phosphatase activity. All patients had markedly reduced PtdIns(4,5)P2 5-phosphatase activity in their fibroblasts, whereas the ocrl1 protein was detectable by immunoblotting in some patients with either missense mutations or a codon deletion but was not detectable in those with premature termination mutations. These results confirm and extend our previous observation that the OCRL phenotype results from loss of function of the ocrl1 protein and that mutations are generally heterogeneous. Missense mutations that abolish enzyme activity but not expression of the protein will be useful for studying structure-function relationships in PtdIns(4,5)P2 5-phosphatases.     

MR findings in oculocerebrorenal syndrome

Oculocerebrorenal syndrome is an X-linked recessive disorder characterized by congenital ocular abnormalities, mental retardation, renal disease, and metabolic bone disease. We report a case of oculocerebrorenal syndrome and, using T1-, proton density-, and T2-weighted imaging sequences, are able to characterize two distinct white matter abnormalities: one lesion is punctate and has signal characteristics that parallel that of cerebrospinal fluid; a second lesion, found in association with the first, consists of patchy white matter abnormalities that are hypointense on T1-weighted images but hyperintense on proton density- and T2-weighted images.     

Splicing defects in the COL3A1 gene: marked preference for 5' (donor) spice-site mutations in patients with exon-skipping mutations and Ehlers-Danlos syndrome type IV

Ehlers-Danlos syndrome (EDS) type IV results from mutations in the COL3A1 gene, which encodes the constituent chains of type III procollagen. We have identified, in 33 unrelated individuals or families with EDS type IV, mutations that affect splicing, of which 30 are point mutations at splice junctions and 3 are small deletions that remove splice-junction sequences and partial exon sequences. Except for one point mutation at a donor site, which leads to partial intron inclusion, and a single base-pair substitution at an acceptor site, which gives rise to inclusion of the complete upstream intron into the mature mRNA, all mutations result in deletion of a single exon as the only splice alteration. Of the exon-skipping mutations that are due to single base substitutions, which we have identified in 28 separate individuals, only two affect the splice-acceptor site. The underrepresentation of splice acceptor-site mutations suggests that the favored consequence of 3' mutations is the use of an alternative acceptor site that creates a null allele with a premature-termination codon. The phenotypes of those mutations may differ, with respect to either their severity or their symptomatic range, from the usual presentation of EDS type IV and thus have been excluded from analysis.     

Characterization of nine novel mutations in the CD40 ligand gene in patients with X-linked hyper IgM syndrome of various ancestry

X-linked immunodeficiency with hyper-IgM (HIGMX-1) is a rare disorder caused by defective expression of the CD40 ligand (CD40L) by activated T lymphocytes, resulting in inefficient T-B cell cooperation and failure of B cells to undergo immunoglobulin isotype switch. In the present work, we describe nine patients of various ancestry who bear different mutations in the X chromosome-specific CD40L gene. Two of the mutations were nonsense mutations, one each resulting in premature stop codons at amino acid residues 39 and 140. Three patients had single point missense mutations, one each at codons 126, 140, and 144. Another patient had a 4-bp genomic deletion in exon 2, resulting in a frameshift and premature termination. Three patients showed insertions, one each of 1, 2, and 4 nt, probably because of polymerase slippage, resulting in frameshift mutation and premature termination. Overall, these observations confirm the heterogeneity of mutations in HIGMX-1. However, the identification of two patients whose mutation involves codon 140 (previously shown to be altered in two other unrelated subjects) suggests that this may be a hotspot of mutation in HIGMX-1. In two additional patients with clinical and immunological features indistinguishable from canonical HIGMX-1, no mutation was detected in the coding sequence, in the 5' flanking region, or in the 3' UTR.     

Low frequency of somatic mutations in the LKB1/Peutz-Jeghers syndrome gene in sporadic breast cancer

Germ-line mutations in the LKB1 gene on chromosome 19p are responsible for most cases of the Peutz-Jeghers syndrome, in which intestinal hamartomas are associated with elevated risks of several cancer types, including breast cancer. We have evaluated the role of somatic mutations in LKB1 in breast cancer. Of 40 informative primary breast cancers, 3 showed loss of heterozygosity on chromosome 19p in the vicinity of LKB1, and no somatic mutations of LKB1 were observed in 62 primary breast cancers and 17 established breast cancer cell lines. The results indicate that mutations in LKB1 do not play an important role in the development of sporadic breast cancer.     

Alteration of the LIS1 gene in Japanese patients with isolated lissencephaly sequence or Miller-Dieker syndrome

Maffucci's syndrome is a rare, congenital disease due to neuro-ectodermal dysplasia and is characterized by enchondromatosis and multiple soft tissue haemangiomata. A case of Maffucci's syndrome with haemangiomata along the upper airways requiring laser surgery is described. The literature on Maffucci's syndrome is reviewed.     

Identification of 12 novel mutations in the alpha-N-acetylglucosaminidase gene in 14 patients with Sanfilippo syndrome type B (mucopolysaccharidosis type IIIB)

Sanfilippo syndrome type B or mucopolysaccharidosis type IIIB (MPS IIIB) is one of a group of lysosomal storage disorders that are characterised by the inability to breakdown heparan sulphate. In MPS IIIB, there is a deficiency in the enzyme alpha-N-acetylglucosaminidase (NAGLU) and early clinical symptoms include aggressive behaviour and hyperactivity followed by progressive mental retardation. The disease is autosomal recessive and the gene for NAGLU, which is situated on chromosome 17q21, is approximately 8.5 kb in length and contains six exons. Primers were designed to amplify the entire coding region and intron/exon boundaries of the NAGLU gene in 10 fragments. The PCR products were analysed for sequence changes using SSCP analysis and fluorescent DNA sequencing technology. Sixteen different putative mutations were detected in DNA from 14 MPS IIIB patients, 12 of which have not been found previously. The mutations include four deletions (219-237del19, 334-358del25, 1335delC, 2099delA), two insertions (1447-1448insT, 1932-1933insGCTAC), two nonsense mutations (R297X, R626X), and eight missense mutations (F48C, Y140C, R234C, W268R, P521L, R565W, L591P, E705K). In this study, the Y140C, R297X, and R626X mutations were all found in more than one patient and together accounted for 25% of mutant alleles.     

Resistance-related mutations in the HIV-1 protease gene of patients treated for 1 year with the protease inhibitor ritonavir (ABT-538)

OBJECTIVE: To define genotypic and phenotypic resistance patterns following prolonged therapy with the protease inhibitor ritonavir (ABT-538). DESIGN: Seven HIV-1-infected patients, all but one previously treated with dideoxynucleoside analogues (zidovudine, didanosine, zalcitabine), were treated for 1 year with ritonavir. METHODS: Direct solid-phase sequencing of the protease gene starting from plasma derived viral RNA followed by comparison to phenotypic drug resistance data. RESULTS: The most frequent amino-acid substitutions occurring upon administration of the protease inhibitor were V82A/F (substrate binding site), I54V (flap region), A71V and L10I. Additional mutations found in more than one patient were I15V, M36I, I84V and I93L. Mutation L63P was found both in pre- and post-ritonavir samples. Phenotypic drug resistance assays confirmed resistance to ritonavir in post-treatment samples (approximately 170-fold) and showed cross-resistance to indinavir (approximately 30-fold) and partially to saquinavir (approximately fivefold). At 1 year of treatment, one patient without known resistance-associated mutations in the protease gene still showed a substantial rise in CD4 cell count accompanied by a more than 2.4 log decrease in RNA viral load. However, at week 78, mutations R8Q, E34K, R57K, L63P and I84V were detected and the treatment benefit was partially lost. CONCLUSIONS: Long-term treatment with ritonavir is associated with the emergence of multiple mutations in the HIV-1 protease gene. The mutations L10I, I54V, L63P, A71V, V82A/F and I84V correspond to known drug-resistance mutations for ritonavir and other protease inhibitors. Phenotypic resistance to ritonavir was detected in a majority of ritonavir-treated patients at 1 year of treatment. In addition, long-term ritonavir treatment selects for cross-resistance to the protease inhibitors indinavir and saquinavir. This argues against sequential therapy with several protease inhibitors. Delayed resistance in one patient was accompanied with a prolonged increase in CD4 cell count and decrease in viral load suggesting a temporary benefit of treatment.     

Mutation analysis of LMX1B gene in nail-patella syndrome patients

Nail-patella syndrome (NPS), a pleiotropic disorder exhibiting autosomal dominant inheritance, has been studied for >100 years. Recent evidence shows that NPS is the result of mutations in the LIM-homeodomain gene LMX1B. To determine whether specific LMX1B mutations are associated with different aspects of the NPS phenotype, we screened a cohort of 41 NPS families for LMX1B mutations. A total of 25 mutations were identified in 37 families. The nature of the mutations supports the hypothesis that NPS is the result of haploinsufficiency for LMX1B. There was no evidence of correlation between aspects of the NPS phenotype and specific mutations.     

Hemizygous deletion of the HPC-1/syntaxin 1A gene (STX1A) in patients with Williams syndrome

HPC-1/syntaxin 1A is a membrane protein that plays an important role in exocytosis of neurotransmitters from neuronal cells. We previously mapped the human HPC-1/syntaxin 1A gene (STX1A) to chromosome 7q11.2, which is within the Williams syndrome (WS) region. Here, we performed FISH analysis on 46 patients with WS to examine the relationship between STX1A and WS. Our results showed a hemizygous deletion of the HPC-1/syntaxin 1A gene in each patient, suggesting that the neurological symptoms of WS may be related to the hemizygous deletion of STX1A.     

Molecular analysis of HLA-H gene mutations in New Zealand patients with haemochromatosis

AIM: To determine the frequency of HLA-H gene mutations in New Zealand patients with haemochromatosis. METHODS: The Cys282Tyr and His63Asp mutations in the HLA-H gene were analyzed by polymerase chain reaction, restriction enzyme digestion and electrophoresis in two separate patient groups. The first was a group of 20 Christchurch patients with a definite clinical diagnosis of haemochromatosis. The second group consisted of 33 patients, with a provisional diagnosis of haemochromatosis, attending Dunedin Hospital for therapeutic venesection. RESULTS: All 20 Christchurch patients and 25 of the 33 (76%) Dunedin patients were homozygous for the Cys282Tyr mutation. After review of the clinical data, histology and response to venesection a diagnosis of haemochromatosis could be confidently excluded in six of the remaining eight patients. Despite atypical features, a diagnosis of haemochromatosis could not be excluded in the final two patients, one of whom was a compound heterozygote for the two mutations. CONCLUSIONS: Homozygosity for the Cys282Tyr mutation is closely associated with haemochromatosis in New Zealand patients. Molecular analysis of the HLA-H gene is indicated in the assessment of patients with iron overload including those currently being treated by venesection.     

First report of prenatal biochemical diagnosis of Lowe syndrome

The oculocerebrorenal syndrome of Lowe (OCRL) is a rare X-linked disorder with a severe phenotype characterized by congenital cataracts, renal tubular dysfunction and neurological deficits. The gene has been characterized and mutations have been identified in patients. Owing to the allelic heterogeneity exhibited by this gene, prenatal diagnosis by molecular analysis is limited to families in which the mutation is already known or in which linkage is informative. A more generally applicable diagnostic test would be valuable for families at risk for Lowe syndrome. Since ocrl1 is now known to encode a phosphatidylinositol 4,5-bisphosphate 5-phosphatase (Ptdlns(4,5)P2 phosphatase), we assessed whether biochemical testing could be used for prenatal diagnosis. We report here the first case of prenatal diagnosis for Lowe syndrome by measuring phosphatidylinositol 4,5-bisphosphate 5-phosphatase activity in cultured amniocytes.     

Systematic screening for mutations in the human serotonin 1F receptor gene in patients with bipolar affective disorder and schizophrenia

We determined the relative minimal inhibitory and minimal amoebicidal concentrations of chlorhexidine digluconate and polyhexamethylene biguanide for four species of Acanthamoeba. The amoebae were grown in peptone-glucose-yeast extract broth for 72 h in tissue culture flasks. Either washed trophozoites (approximately 10(5)) or cysts (approximately 10(5)) were incubated in the enrichment broth in 96 well microtiter trays. Antimicrobial concentrations of the biguanides were determined from microscopic examinations of methylene blue uptake and from subcultures. In general, killing was time dependent. Minimal amoebicidal concentrations at 24 h ranged from 50 to 100 mg/ml and to as low as 25 mg/ml by 72 h. Trophozoites were killed more rapidly than cysts. Both biguanides had similar levels of activity. A synergistic combination of chlorhexidine and polyhexamethylene biguanide (total concentration 25 mg/ml) was most evident for A. castellanii and A. polyphaga. Cysts of A. culbertsoni and A. hatchetti stained more rapidly after exposure to the combination of biguanides than to the single biguanides, but there were no statistically significant differences in the final numbers of dead or stained cysts after exposure to the combination or to the single biguanides.