Unexpected extradermatological findings in 31 patients with xeroderma pigmentosum type C

BACKGROUND

Xeroderma pigmentosum type C (XP-C) is a rare, autosomal, recessive condition characterized by the association of various clinical manifestations mostly involving the skin and eyes.

OBJECTIVES

To evaluate the clinical manifestations in a homogeneous, genetically characterized cohort of patients with XP-C.

METHODS

All patients with XP-C, which was confirmed genetically or by unscheduled DNA synthesis, from the registry of our department and from the French association of patients 'Les Enfants de la Lune' were contacted. During a planned consultation, clinical information was collected using a standardized case-record form.

RESULTS

In total, 31 patients were seen. The mean age at diagnosis was 2.95 years; skin symptoms started at a mean age of 1.49 years. Among the patients, 52% had relatively short stature, with a height-for-weight z-score below -1 SD; 62% showed pyramidal syndrome and 45% had photophobia and/or conjunctivitis. Four patients had several pyogenic granulomas. Twenty-four patients (77%) had skin cancer. The mean age of onset of the first skin cancer was 4.76 years (range 2-14.5 years). Basal-cell carcinoma was the most frequent cancer. Melanomas were rare and mostly desmoplastic. Multinodular thyroid was the most frequent internal tumour.

CONCLUSIONS

Our data highlight several new aspects of XP-C. Patients with XP-C are at risk of developing pyogenic granulomas, desmoplastic melanomas and multinodular thyroid. Involvement of the central nervous system is frequent, but its mechanism remains unclear. The relatively short stature of the patients needs further investigation in order to be explained. XP-C is not only a cancer-prone disorder but is also a polysystemic disorder.

Intragenic rearrangements in LARGE and POMGNT1 genes in severe dystroglycanopathies

Dystroglycanopathies are a heterogeneous group of muscular dystrophies with autosomal recessive inheritance characterized by abnormal glycosylation of alpha-dystroglycan. The most severe phenotypes are Walker-Warburg Syndrome (WWS) and muscle-eye-brain disease (MEB) presenting with lissencephaly type II (LIS II) and in which muscular dystrophy is associated with mental retardation and eye abnormalities. To date, six distinct genes, POMT1, POMT2, POMGNT1, FKTN, FKRP, LARGE and recently in one case DPM3, have been shown to be involved in dystroglycanopathies. Genomic sequencing alone is still frequently used for diagnosis purpose, not allowing detection of intragenic rearrangements at the heterozygous state contrarily to RNA analysis, quantitative PCR and CGH array analysis. These latter methods enabled us to identify four new intragenic rearrangements in the LARGE gene in three fetuses with WWS, born to two unrelated families: deletion of exons 9-10 and duplication of introns 1-4 for the first family and deletion of exons 4 and 7 for the second one; and a deletion of the last six exons of the POMGNT1 gene in two unrelated MEB patients. Genomic dosage studies using emerging tools such as CGH array should be included in routine molecular analysis of dystroglycanopathies, not only for the screening of the LARGE gene in which this kind of mutation seems to be more frequent than point mutations, but also for the other involved genes, especially in severe clinical cases.

EDNRB gene variants and melanoma risk in two southern European populations

BACKGROUND

EDNRB gene variants were reported to be associated with melanoma risk in French patients, with the S305N variant showing the highest frequency.

AIM

To verify the S305N association with melanoma risk in an independent larger French population (378 patients, 389 controls); to investigate the role of EDNRB variants in melanoma risk in an Italian population (133 patients, 118 controls); and to explore the association of CDKN2A or CDK4 mutations with the S305N EDNRB variant in a subgroup of patients (59 French, 12 Italian) with a suspected hereditary predisposition to melanoma (familial melanoma, sporadic multiple primary melanoma or melanoma associated with pancreatic cancer).

METHODS

The S305N variant was genotyped in the French population, while the EDNRB gene in the Italian population was entirely sequenced.

RESULTS

Overall, there was no significant difference in the frequency of the S305N variant between patients with sporadic melanoma and controls in either the French or the Italian population. However, a significantly higher S305N allele frequency was detected in French patients with a suspected hereditary predisposition to melanoma compared with controls (P = 0.04). In addition, in this subgroup of patients, the S305N allele was also significantly associated with the presence of CDKN2A mutations (P = 0.04).

CONCLUSIONS

Our results showed no evidence of association of the S305N EDNRB polymorphism with sporadic melanoma risk in either the French or Italian populations, but there was an indication that EDNRB might be a melanoma-predisposing gene in French patients with a suspected hereditary predisposition to melanoma.

[Intra- and interfamilial phenotype variation in Birt-Hogg-Dubé syndrome: Consequences for therapy]

BACKGROUND

Birt-Hogg-Dubé syndrome (BHDS) is an autosomal-dominantly inherited genodermatosis that predisposes to the development of benign hair follicle tumours, lung cysts, kidney tumours, and possibly colonic cancers, due to mutations in the FLCN gene. We report cases involving a new mutation in three unrelated families.

MATERIALS AND METHODS

Blood samples of three probands were submitted for a molecular diagnosis of BHDS. Following DNA extraction, FLCN gene sequencing was performed. The identified mutations were confirmed on a second sample. A cancer genetics consultation was organized and specific tests (dermatological examination, CT scan of chest and abdomen and colonoscopy) were proposed for each BHDS patient.

RESULTS

FLCN gene-sequencing analysis revealed an identical complex harmful mutation in all three families. The first proband showed fibrofolliculomas (FF), a history of pneumothorax and colonic adenoma. The mutation was found in a brother and two sisters, who were asymptomatic, and in a niece with FF. The second proband showed FF. The mutation was found in her mother, who had FF. The third proband presented diffuse emphysema and very rare FF.

DISCUSSION

This case report shows extremely wide intra- and interfamilial phenotype variation within individuals having a similar FLCN gene mutation. In large cohorts of BHDS patients, no genotype-phenotype correlation has been shown. This case emphasises the vital importance of presymptomatic diagnosis for each member of a BHDS family by means of a cancer genetics consultation, followed by a CT scan of the chest and abdomen, colonoscopy and annual kidney imaging.

Xeroderma pigmentosum group C in a French Caucasian patient with multiple melanoma and unusual long-term survival

We report the case of an 83-year-old French woman with multiple melanomas showing a severe DNA repair deficiency, corrected after transfection by XPC cDNA. Two biallelic mutations in the XPC gene are reported: an inactivating frameshift mutation in exon 15 (c.2544delG, p.W848X) and a missense mutation in exon 11 (c.2108 C>T, P703L). We demonstrate that these new mutations are involved in the DNA repair deficiency and confirm the diagnosis of xeroderma pigmentosum from complementation group C (XP-C). We speculate that the coexistence of a MC1R variant may be involved in the phenotype of multiple melanomas and that the unusual long-term survival may be related to a lower ultraviolet radiation exposure and to a regular clinical follow-up. This patient appears to be the first French Caucasian XP-C case and one of the oldest living patients with XP reported worldwide.

MC1R variants and melanoma risk: First study on Melan-Cohort

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Background: The presence of functional variants of MC1R, has been shown to be associated with melanoma (MM) risk in different populations worldwide. We had previously shown in a first case - control pilot study that MC1R variants were associated the risk of melanoma (MM) in France. Methods: In order to confirm and precise these results on a larger sample, we performed a case-control study with patients from Melan-Cohort, a prospective cohort from the Paris’ region. After signature of informed consents and extraction of blood DNAs, MC1R variants were sought by automatic sequencing in 270 patients (95 familial MM, 54 multiple sporadic MM, and 121 ‘single‘ MM) and in 154 controls sex, age, and ethnic matched. Usual statistical calculations (Chi2, odd ratios, logistic regression) were carried out. Results: MC1R functional variants were present in 73% of the patients versus 43% of controls (p<0.0001). The presence of only one variant was significantly associated with melanoma risk (OR 2.9 [1.88–4.5]), and the presence of two variants doubled the risk (OR, 6.91 [3.33–14.3]). Furthermore, each of the seven variants, RHC (i.e associated with the Red Hair Phenotype; R142H, R151C, R160W, D294H) or non-RHC (V92M, V60L, R163Q) was individually associated with melanoma risk (OR ranging from 2.8 to 14). The frequency of variants was similar in each sub-group of MM examined (familial, multiple sporadic, or ‘single‘). However, RHC variants were significantly more frequent in the familial subgroup (p = 0.0045) and non RHC were significantly more frequent in the “single” MM subgroup (p = 0.0006). In addition, we confirm that the risk related to MC1R largely persisted after stratification on each clinical risk factor: hair and eyes color, skin type, and nevi count. On the other hand, there was no association between the presence of MC1R variant and the histological type of MM, the age at diagnosis, and the Breslow index. Conclusion: Our results confirm the important role of MC1R on melanoma risk in France and this independently of clinical risk factors. Surprisingly, both RHC and non-RHC variants were associated with melanoma risk, but RHC variants have possibly a higher penetrance. Finally, the presence of MC1R variants does not seem to be correlated with the speed of evolution (Breslow index) of melanoma.

No significant financial relationships to disclose.

PTCH mutations and deletions in patients with typical nevoid basal cell carcinoma syndrome and in patients with a suspected genetic predisposition to basal cell carcinoma: a French study

The patched (PTCH) mutation rate in nevoid basal cell carcinoma syndrome (NBCCS) reported in various studies ranges from 40 to 80%. However, few studies have investigated the role of PTCH in clinical conditions suggesting an inherited predisposition to basal cell carcinoma (BCC), although it has been suggested that PTCH polymorphisms could predispose to multiple BCC (MBCC). In this study, we therefore performed an exhaustive analysis of PTCH (mutations detection and deletion analysis) in 17 patients with the full complement of criteria for NBCCS (14 sporadic and three familial cases), and in 48 patients suspected of having a genetic predisposition to BCC (MBCC and/or age at diagnosis ⩽40 years and/or familial BCC). Eleven new germline alterations of the PTCH gene were characterised in 12 out of 17 patients harbouring the full complement of criteria for the syndrome (70%). These were frameshift mutations in five patients, nonsense mutations in five patients, a small inframe deletion in one patient, and a large germline deletion in another patient. Only one missense mutation (G774R) was found, and this was in a patient affected with MBCC, but without any other NBCCS criterion. We therefore suggest that patients harbouring the full complement of NBCCS criteria should as a priority be screened for PTCH mutations by sequencing, followed by a deletion analysis if no mutation is detected. In other clinical situations that suggest genetic predisposition to BCC, germline mutations of PTCH are not common.

Mild dehydrated hereditary stomatocytosis revealed by marked hepatosiderosis

We report a patient in whom hepatosiderosis was diagnosed at the age of 55 years and who has since been treated by regular bleeding. The H63D mutation was found in the heterozygous state in the HFE gene. No mutation was recorded in the SLC11A3 gene (ferroportin). Hepatosiderosis did not seem primary, nevertheless its cause long remained elusive. Only 2 years ago did we find the responsible condition, a very mildly expressed form of dehydrated hereditary stomatocytosis (DHS). This genetic disease is a strongly iron-loading condition. Haemolysis was fully compensated. Kalaemia was slightly elevated, suggesting a pseudohyperkalaemia that may be associated with DHS. Osmotic gradient ektacytometry allowed to assess the diagnosis of DHS. The red cell monovalent Na+ and K+ concentrations were moderately elevated and reduced respectively. The temperature dependence of the ouabain + bumetanide-resistant K+ influx produced a shallow slope, above and parallel to the control curve. These features were consistent with the diagnosis of DHS. The pronounced hepatosiderosis contrasted with the mildly expressed DHS, and with the ferritinaemia that was slightly elevated, if at all, prior to bleeding. Bleeding caused ferritinaemia to decrease and hepatosiderosis to recede. The whole picture accounts for a misleading presentation of DHS, in which the primary condition long remained hidden behind one of its remotest complications, hepatosiderosis.

Germline mutations of the INK4a-ARF gene in patients with suspected genetic predisposition to melanoma

Germline anomalies of the INK4a-ARF and Cdk4 genes were sought in a series of 89 patients suspected of having a genetic predisposition to melanoma. Patients were selected based on the following criteria: (a) familial melanoma (23 cases), (b) multiple primary melanoma (MPM; 18 cases), (c) melanoma and additional unrelated cancers (13 cases), (d) age at diagnosis less than 25 years (21 cases), and (e) nonphoto-induced melanoma (NPIM; 14 cases). Mutations of INK4a-ARF and Cdk4 were characterised by automated sequencing, and germline deletions of INK4a-ARF were also examined by real-time quantitative PCR. Seven germline changes of INK4a-ARF, five of which were novel, were found in seven patients (8%). Four were very likely to be pathogenic mutations and were found in three high-risk melanoma families and in a patient who had a pancreatic carcinoma in addition to melanoma. Three variants of uncertain significance were detected in one MPM patient, one patient <25 years, and one NPIM patient. No germline deletion of INK4a-ARF was found in 71 patients, and no Cdk4 mutation was observed in the 89 patients. This study confirms that INK4a-ARF mutations are infrequent outside stringent familial criteria, and that germline INK4a-ARF deletions are rarely involved in genetic predisposition to melanoma.

[Polymorphism of aldose reductase gene and susceptibility to retinopathy and nephropathy in Caucasians with type 1 diabetes]

Polymorphisms of the -106 mutation and z - 2 or z + 2 microsatellites (-2.1 kb) of the Aldose Reductase (AR) gene have been associated to microangiopathic complications of the diabetes mellitus. The study aimed to establish a relation between the occurrence and progression of the renal and retinal complications and these polymorphisms. The genotypes were realised in 3 populations: DESIR (n = 369), non-diabetic control subjects from the general French population: GENEDIAB (n = 494), type 1 diabetic patients who are suffering from proliferative retinopathy associated with a variable seriousness nephropathy (absent: n = 157; incipient: n = 104; established: n = 126; advanced: n = 107); SURGENE (n = 310), type 1 diabetic patients whom the renal status is prospectively assessed since 1989 in one single center Angers University Hospital. The genotype of the -106 polymorphism was determined using the Molecular Beacons. For the microsatellites analysis, we used an automatized method (GeneScan Abi Prism 3100). There was a strong linkage disequilibrium between the z - 2 allele and the T allele (chi 2 = 120; p = 0.001). The frequency of the C-106T is similar for the DESIR and GENEDIAB cohorts (chi 2 = 3.32; p = 0.19); the Hardy Weinberg law was verified in this group (chi 2 = 0.001, 0.9; p = 1.5 and 0.5 respectively). The law was not verified for the SURGENE cohort (chi 2 = 4.7; p = 0.03) where the frequency of the TT genotype was significantly more important compared to the DESIR population (chi 2 = 6.4; p = 0.01). The z, z - 2 and z + 2 alleles was more frequent compared with other alleles (n = 909, 830 and 349; 39, 38 and 15%). The frequency of the C-106T and microsatellites genotypes did not parallel the nephropathy staging in the GENEDIAB population (chi 2 = 10.9, 2.7, 2.4; p = NS respectively). In the SURGENE population, the survival without renal events did not differ according C-106T and z - 2 or z + 2 microsatellites genotypes (log-rank: 0.6, 3.9, 0.1; p = NS respectively). At the end of the follow-up, we found an effect of the -106 mutation and of the z - 2 microsatellite on the staging of the retinopathy (chi 2 tendency test = 4.61, 0.12; p = 0.031, 0.02; 6 d.f., respectively). The logistic regression multivariable analysis shows that the retinopathy during the final evaluation is independently explained by several factors: diabetes duration (p < 0.0001; OR 21.756; 95% CI: 7.024-67.389), presence of nephropathy (p < 0.0001; OR: 4.086; 95% CI: 2.094-7.973), and genotype TT (p = 0.011; OR: 0.38; 95% CI: 0.18-0.803). In contrast, age of diabetes onset (p = 0.112; OR: 1.556; 95% CI: 0.9-2.692), median HbA1c (p = 0.164; OR: 1.479; 95% CI: 0.85-2.576) and sex (p = 0.156; OR: 1.495; 95% CI: 0.856-2.612) have no independent effect. In conclusion, the association of these AR genetic variants seems absent about the renal risk and slight about the retinal risk associated to the type 1 diabetes mellitus.

Quantification of TEL-AML1 transcript for minimal residual disease assessment in childhood acute lymphoblastic leukaemia

Strategies currently used for residual disease detection in acute lymphoblastic leukaemia (ALL) rely on polymerase chain reaction (PCR) detection of immunoglobulin and T-cell receptor rearrangements. The TEL-AML1 fusion transcript, which is associated with t(12;21) (p13;q22), is found in 25% of childhood B-cell precursor ALL, and represents an interesting alternative target. We compared two methods for quantitating TEL-AML1 fusion transcripts: competitive PCR and real-time PCR. These techniques showed similar sensitivity (5 x 10(-5)) and reproducibility. Giving highly correlated results, both techniques can be conveniently used for TEL-AML1 transcript quantification. The constancy of TEL-AML1 expression was evaluated by measuring TEL-AML1 transcripts at different steps of the cell cycle, and in 21 cases of ALL at diagnosis. No major variation in TEL-AML1 expression was observed during the cell cycle or in 20/21 of the ALL patients. Residual disease was then determined after completion of induction therapy in 20 patients with a TEL-AML1-positive ALL. Seven patients out of 20 (35%) were still positive, including two patients with high level of residual blasts (close to or beyond 10(-2)). When comparison was possible, results obtained using TEL-AML1 quantification were in accordance with those obtained using T-cell receptor rearrangements analysis.

Characterization of 11 novel mutations in the X-linked chronic granulomatous disease (CYBB gene)

The most frequent form of chronic granulomatous disease (CGD) is caused by inactivation of the CYBB gene, which encodes the gp91-phox subunit of phagocyte NADPH oxidase. This defect prevents phagocytes from producing reactive oxygen species and thus from eradicating bacterial and fungal infections. We investigated 16 unrelated male patients with suspected X-linked CGD and gp91-phox deficiency. A mutation was found in the CYBB gene of all 16 patients, and 11 of these mutations were novel. Eleven patients (69%) had a point mutation (84G>A in two unrelated patients, and 177C>G, 217C>T, 388C>T, 676C>T, 691C>T, 868C>T, 919A>C, 1384G>T and T1514G in one case each, yielding W28X, C59W, R73X, R130X, R226X, Q231X, R290X, T307P, E462X, L505R gp-91phox). One patient had an in-frame deletion removing two amino acids (R54 and A55). Finally, insertions or duplications were found in four patients (from +1 to +31 bases). Overall, 12 (75%) of the mutations led to the production of a truncated protein. No clear correlation was found between clinical manifestations and genomic/biochemical alterations. Thirteen mothers could be tested, and all were carriers. Hum Mutat 18:163, 2001.

Lack of hepcidin gene expression and severe tissue iron overload in upstream stimulatory factor 2 (USF2) knockout mice

We previously reported the disruption of the murine gene encoding the transcription factor USF2 and its consequences on glucose-dependent gene regulation in the liver. We report here a peculiar phenotype of Usf2(-/-) mice that progressively develop multivisceral iron overload; plasma iron overcomes transferrin binding capacity, and nontransferrin-bound iron accumulates in various tissues including pancreas and heart. In contrast, the splenic iron content is strikingly lower in knockout animals than in controls. To identify genes that may account for the abnormalities of iron homeostasis in Usf2(-/-) mice, we used suppressive subtractive hybridization between livers from Usf2(-/-) and wild-type mice. We isolated a cDNA encoding a peptide, hepcidin (also referred to as LEAP-1, for liver-expressed antimicrobial peptide), that was very recently purified from human blood ultrafiltrate and from urine as a disulfide-bonded peptide exhibiting antimicrobial activity. Accumulation of iron in the liver has been recently reported to up-regulate hepcidin expression, whereas our data clearly show that a complete defect in hepcidin expression is responsible for progressive tissue iron overload. The striking similarity of the alterations in iron metabolism between HFE knockout mice, a murine model of hereditary hemochromatosis, and the Usf2(-/-) hepcidin-deficient mice suggests that hepcidin may function in the same regulatory pathway as HFE. We propose that hepcidin acts as a signaling molecule that is required in conjunction with HFE to regulate both intestinal iron absorption and iron storage in macrophages.

Association studies between haemochromatosis gene mutations and the risk of cardiovascular diseases

BACKGROUND

Haemochromatosis is a common genetic disorder, inherited as an autosomal recessive trait that results in a progressive accumulation of iron in most tissues of the body. Positive association studies have been recently published between cardiovascular diseases and heterozygosity for the major mutation C282Y in the haemochromatosis gene HFE.

METHODS

In the present work, we have determined the HFE genotypes for C282Y and H63D in subjects from two case-control studies: the ECTIM and GENIC studies, designed to identify genetic variants associated with myocardial and brain infarction, respectively. In addition, we tested whether HFE mutations were associated with the degree of arteriosclerosis assessed non-invasively by Doppler ultrasonography on the carotid and femoral arteries, in a group of apparently healthy individuals (the AXA Study).

RESULTS

The prevalence of 282Y, and 63D allele carriers, did not differ between cases and controls in the ECTIM and in the GENIC studies, while 63D but not 282Y carriers were more numerous among subjects with atherosclerotic plaques in the AXA Study.

CONCLUSIONS

These three studies do not provide consistent evidence supporting the hypothesis that HFE mutations are associated with an increased risk of cardiovascular disease and with the development of arteriosclerosis.

Deletion of chromosomal region 13q14.3 in childhood acute lymphoblastic leukemia

Deletion of the 13q14 chromosomal region is frequent in B cell chronic lymphocytic leukemia (B-CLL) and is believed to inactivate a tumor supressor gene (TSG) next to RB1. We studied microsatellite markers spanning the 13q14 chromosomal region in 138 children with acute lymphoblastic leukemia (ALL). Allelic loss was demonstrated in six cases (4.3%). Deletion did not include RB1 in two cases. In five patients, the deleted region overlapped that described in B-CLL. A sixth patient harbored a smaller deletion, slightly more telomeric than minimal deleted regions reported in B-CLL. Apparent differences in the delineation of the minimal deleted region could be due to the fact that the putative TSG is a very large gene, with some deletions affecting only a part of it. Our present findings suggest that at least some of its exons lie within a region of less than 100 kb more telomeric that previously thought.

Coinheritance of two alpha-spectrin gene defects in a recessive spherocytosis family

We studied a recessive hereditary spherocytosis (HS) family from Norway in which all four children had haemolytic spherocytosis while spectrin (Sp) deficiency was detected in the proband. Molecular analysis demonstrated that all affected children had inherited the low expression alpha-Sp allele LEPRA (Low Expressed PRAgue) from the father. Haplotyping with a polymorphic dinucleotide repeat for the alpha-Sp gene (alphaVNTR) located in the 3' untranslated region of mRNA showed that all recessive children had inherited the same maternal alpha-spectrin allele. The paternal Sp-alphaLEPRA allele was found in cis of the polymorphic alpha-Sp Bughill allele (alphaBH) characterized by the A970D point mutation in the Sp alpha-chain. This mutation was identified on two-dimensional electrophoresis of Sp tryptic digests as an acidic shift of the alphaII tryptic domains (spots alphaIIa). Analyses of the relative expression of the paternal alpha-Sp Bughill polymorphism in the proband showed that the product of the maternal alpha-Sp gene is almost completely absent from the mature erythrocyte membrane. Comparative analysis between alphaVNTR PCR-amplified from genomic DNA and from cDNA showed that the maternal low expression alpha-Sp allele is associated with a decreased amount of mRNA. Results from molecular and biochemical studies showed that all the affected children of this family are compound heterozygous for two different low expression alpha-Sp alleles: an uncharacterized defective alpha-Sp allele on the maternal side and an alphaLEPRA allele tagged by the alphaIIa polymorphism on the paternal side.

Genotype determination at the survival motor neuron locus in a normal population and SMA carriers using competitive PCR and primer extension

Precise quantitation of SMN1 copy number is of great interest in many clinical applications such as direct detection of SMA carriers or detection of an SMA-affected patient with a hemizygous deletion of the SMN1 gene. We describe a method that combines two independent nonradioactive PCR assays: determination of the relative ratio of the SMN1 and SMN2 genes using a primer extension assay and of the total SMN copy number using competitive PCR. Consistency of the results of two independent approaches ensures the reliability of the deduced genotype and thus avoids false interpretation of borderline results that can occur in quantitative assays. In all, 135 subjects were tested, including 91 normal controls and 44 SMA-affected children or SMA carriers. Two main genotypes were observed in controls: 2T/2C (45%) and 2T/1C (32%). A wide variability at the SMN locus is observed with nine different genotypes and up to six SMN genes. SMA carriers showed three frequent genotypes, 1T/2C (50%), 1T/3C (29%), and 1T/1C (18%). Normal chromosomes with two SMN1 genes per chromosome are not infrequent and thus, about 3% of SMA carriers are not detected using SMN1 copy number quantitation. Finally, as this method does not detect point mutations (4% of SMN1 gene mutations), reliability ranges from 93% to 100% depending on data available from the propositus.

Identification of four novel PMM2 mutations in congenital disorders of glycosylation (CDG) Ia French patients

We screened 11 unrelated French patients with congenital disorders of glycosylation (CDG) Ia for PMM2 mutations. Twenty one missense mutations on the 22 chromosomes (95%) including four novel mutations were identified: C9Y (G26A) in exon 1, L32R (TA95GC) in exon 2, and T226S (C677G) and C241S (G722C) in exon 8. We studied the PMM activity of these four novel mutant proteins and of the R141H mutant protein in an E coli expression system. The T226S, C9Y, L32R, and C241S mutant proteins have decreased specific activity (23 to 41% of normal), are all more or less thermolabile, and R141H has no detectable activity. Our results indicate that the new mutations identified here are less severe than the inactive R141H mutant protein, conferring residual PMM activity compatible with life.

Early embryonic lethality of H ferritin gene deletion in mice

Ferritin molecules play an important role in the control of intracellular iron distribution and in the constitution of long term iron stores. In vitro studies on recombinant ferritin subunits have shown that the ferroxidase activity associated with the H subunit is necessary for iron uptake by the ferritin molecule, whereas the L subunit facilitates iron core formation inside the protein shell. However, plant and bacterial ferritins have only a single type of subunit which probably fulfills both functions. To assess the biological significance of the ferroxidase activity associated with the H subunit, we disrupted the H ferritin gene (Fth) in mice by homologous recombination. Fth(+/-) mice are healthy, fertile, and do not differ significantly from their control littermates. However, Fth(-/-) embryos die between 3.5 and 9.5 days of development, suggesting that there is no functional redundancy between the two ferritin subunits and that, in the absence of H subunits, L ferritin homopolymers are not able to maintain iron in a bioavailable and nontoxic form. The pattern of expression of the wild type Fth gene in 9.5-day embryos is suggestive of an important function of the H ferritin gene in the heart.

Absence of microsatellite instability in transitional cell carcinoma of the bladder

OBJECTIVES

To investigate the prevalence of the microsatellite instability related to mismatch repair (MMR) gene defects using a panel of six microsatellite markers, as recommended by a recent workshop on microsatellite instability in colon cancer, because it is still unclear whether abnormalities in DNA MMR genes are involved in transitional cell carcinoma (TCC) of the bladder.

METHODS

Three mononucleotide repeats (BAT26, TGFbetaRII, and BAX) were studied in 33 TCC samples and in four bladder cancer cell lines. Three dinucleotide repeats (D2S123, D5S346, and D17S250) were studied in 21 of these 33 TCC samples.

RESULTS

No alteration was detected either in the 33 TCC samples analyzed or in the four bladder cancer cell lines (T24, J82, 647V, and 1207) studied. A difference between normal and tumor DNA was observed in only 1 of 21 tumor samples for D17S250.

CONCLUSIONS

These data indicate that microsatellite instability is very uncommon in TCC of the bladder.

Recurrent molecular deletion of the 12p13 region, centromeric to ETV6/TEL, in T-cell prolymphocytic leukemia

INTRODUCTION

T-cell prolymphocytic leukemia is a rare form of mature leukemia which occurs in adults and in younger patients suffering ataxia telangiectasia. Among others, complex chromosome aberrations of chromosome 12 have been described in this disease. We searched for deletions of the 12p13 region as the result of these chromosome rearrangements.

MATERIAL AND METHODS

Paired leukemic and non-leukemic cells were obtained from a series of 21 patients suffering T-cell prolymphocytic leukemia. Loss of heterozygosity was searched for by microsatellite typing using a fluorescent automated laser DNA sequencer to analyze the amplification products. Proteins were analyzed by Western blot. Southern blot analysis of one patient was conducted.

RESULTS AND CONCLUSION

Loss of heterozygosity of the 12p13 region, including the ETV6 and CDKN1B genes, was detected in nine of these 21 cases (43%). Western and Southern blot analyses of one case demonstrated a biallelic deletion which did not include ETV6. Taken together, our results defined a minimal region of deletion of less than one Mb flanked by the markers b312C2T7 and D12S320, excluding ETV6 as a candidate gene. Deletion of the 12p13 region is thus a highly recurrent genetic event in T-cell prolymphocytic leukemia.

Mapping of chromosome 20 for loss of heterozygosity in childhood ALL reveals a 1,000-kb deletion in one patient

The long arm of chromosome 20 displays recurrent loss of heterozygosity (LOH) for microsatellite markers in blast cells from children with acute lymphoblastic leukemia. To further characterize the region of deletion and to precisely establish its frequency, we searched for LOH in 103 children with ALL using polymorphic markers in the previously described region of interest, namely between D20S101 and D20S887. LOH was detected in nine patients (ie with a frequency of 8.7%). Interestingly, in one patient, a small deletion was found, flanked proximally by D20S850 and distally by M201, a dinucleotide repeat identified from chromosome 20 sequences. The distance between these two markers is approximately 1000 kb. The occurrence of non-random deletions of the long arm of chromosome 20 has previously been observed in myeloid malignancies (myeloproliferative disorders and myelodysplastic syndromes) in 5-10% of patients. The small deletion in our patient is located within the common region of deletion of myeloproliferative disorders suggesting that a tumor suppressor gene may be the common target of the deletions in various types of hematological malignancies.

Characterization of the 415G>A (E139K) PMM2 mutation in carbohydrate-deficient glycoprotein syndrome type Ia disrupting a splicing enhancer resulting in exon 5 skipping

Carbohydrate-deficient glycoprotein syndrome type Ia (CDGS) is an autosomal recessive disorder, characterized by a central nervous system dysfunction and multiorgan failure associated with defective N-glycosylation and phosphomannomutase (PMM) deficiency related to mutations in the PMM2 gene. A total of 26 different missense mutations and one single base pair deletion have already been described. We found by sequencing and restriction analysis, in two unrelated French patients with CDG type Ia a compound heterozygosity for two mutations in exon 5: a new mutation 415G>A (E139K) and the most frequent mutation 425G>A (R141H ). The 415G>A mutation disrupted a splicing enhancer sequence: (GAR)n-(GAR)n resulting in exon 5 skipping. We studied the activity of these mutant proteins expressed in E Coli. Compared to the normal PMM protein activity, the R141H and transcript without exon 5 expressed a protein with undetectable specific activity when the E139K mutant protein expressed a residual activity of 25%. The E139K mutant protein could be expressed at a sufficient level in vivo to confer residual activity compatible with life in these patients when absence of residual PMM activity is likely lethal.

The red blood cell band 3 variant (band 3Biceêtrel:R490C) associated with dominant hereditary spherocytosis causes defective membrane targeting of the molecule and a dominant negative effect

Hereditary spherocytosis (HS), a common human inherited haemolytic anaemia, is associated with partial deficiency of different erythrocyte membrane proteins. In a subset of dominant HS, a partial membrane expression deficiency of band 3, the erythrocyte anion exchanger (AE1), have previously been characterized, and several mutations in the band 3 gene have been found: amino acid substitutions at conserved positions in the membrane domain, nonsense and frameshift mutations. In HS patients bearing missense mutations, the mutated transcript was present, whereas only the normal transcript was found in HS patients with frameshift mutations. In the former group, the membrane expression deficiency of band 3 was significantly more important than that observed in the latter group of HS patients with frameshift mutations, suggesting that missense mutations may have a dominant negative effect. In the present study, transient and stable transfections of K562 and COS-7 cells were used to demonstrate, by immunoblots of cell lysates and immunofluorescence studies, that the band 3 membrane domain bearing the R490C mutation (band 3Bicetrel) is not targeted to the plasma membrane and is retained in the endoplasmic reticulum. Transient cotransfections of K562 cells with plasmid coding for the normal membrane domain of band 3, together with increasing amounts of plasmid coding for the mutated R490C membrane domain, demonstrated that the band 3 mutant polypeptide exerts a dominant negative effect on the plasma membrane targeting of the normal band 3.