Cloning, characterization and chromosomal localization of the Sus scrofa SLC31A1 gene

Copper is an essential element necessary for normal function of numerous enzymes in all living organisms. Uptake of copper into the cell is thought to occur through the membrane protein, SLC31A1 (CTR1), which has been described in a variety of species including yeast, human and mouse. In this study, we present cloning, gene structure, chromosomal localization and expression pattern of the Sus scrofa SLC31A1 gene, which encodes a 189 amino acid protein. The (SSC) SLC31A1 gene is organized in four exons and spans an approximately 2.3 kb genomic region. We have localized the gene to chromosome 1q28-q2.13 using a somatic cell hybrid panel. This region shows conservation of synteny with human chromosome 9, where the human SLC31A1 (CTR1) gene has been localized. Expression studies suggest that SLC31A1 mRNA is transcribed in all tissues examined.

X-linked recessive Menkes disease: identification of partial gene deletions in affected males

Menkes disease is an X-linked recessive lethal disorder of copper metabolism, caused by defects in the ATP7A gene. Partial gene deletions comprise about 15% of the mutations causing Menkes disease. We have previously demonstrated identification of partial ATP7A deletions in patients by Southern blot analysis. In the present study, we report the use of three fast and reliable polymerase chain reaction (PCR)-based methods for the identification of partial ATP7A deletions in Menkes disease patients. First we demonstrate the use of multiplex PCR, a fast method for identification and rough localization of partial gene deletions, in which two exons of ATP7A are coamplified. Second, we present PCR amplification of genomic DNA across the deletion junctions, a method enabling identification of the deletion breakpoints and hence the exact size of the deletion. Finally, application of reverse transcription PCR (RT-PCR) for identification and localization of gene deletions at the cDNA level is demonstrated. By studying the mutation at the cDNA level the predicted effect of the mutation on the amino acid sequence and consequently the protein structure and function can be inferred. We demonstrate characterization of partial gene deletions in five patients, and in three of these we were able to determine the breakpoint sequences.

High resolution comparative genomic hybridisation analysis reveals imbalances in dyschromosomal patients with normal or apparently balanced conventional karyotypes

A sensitive technique is needed for screening whole genome imbalances in dyschromosomal patients when G-banding shows normal karyotypes or apparently balanced translocations. In this study we performed highly sensitive comparative genomic hybridisation analysis on a number of such cases and revealed chromosomal imbalances in all.

Similar splice-site mutations of the ATP7A gene lead to different phenotypes: classical Menkes disease or occipital horn syndrome

More than 150 point mutations have now been identified in the ATP7A gene. Most of these mutations lead to the classic form of Menkes disease (MD), and a few lead to the milder occipital horn syndrome (OHS). To get a better understanding of molecular changes leading to classic MD and OHS, we took advantage of the unique finding of three patients with similar mutations but different phenotypes. Although all three patients had mutations located in the splice-donor site of intron 6, only two of the patients had the MD phenotype; the third had the OHS phenotype. Fibroblast cultures from the three patients were analyzed by reverse transcriptase (RT)-PCR to try to find an explanation of the different phenotypes. In all three patients, exon 6 was deleted in the majority of the ATP7A transcripts. However, by RT-PCR amplification with an exon 6-specific primer, we were able to amplify exon 6-containing mRNA products from all three patients, even though they were in low abundance. Sequencing of these products indicated that only the patient with OHS had correctly spliced exon 6-containing transcripts. We used two different methods of quantitative RT-PCR analysis and found that the level of correctly spliced mRNA in this patient was 2%-5% of the level found in unaffected individuals. These findings indicate that the presence of barely detectable amounts of correctly spliced ATP7A transcript is sufficient to permit the development of the milder OHS phenotype, as opposed to classic MD.

Expression, purification and copper-binding studies of the first metal-binding domain of Menkes protein

The cDNA, coding for the first metal-binding domain (MBD1) of Menkes protein, was cloned into the T7-system based vector, pCA. The T7 lysozyme-encoding plasmid, pLysS, is shown to be crucial for expression, suggesting that the protein is toxic to the cells. Adding copper to the growth medium did not affect the plasmid stability. MBD1 is purified in two steps with a typical yield of 12 mg.L-1. Menkes protein, a P-type ATPase, contains a sequence GMXCXSC that is repeated six times, at the N-terminus. The paired cysteine residues are involved in metal binding. MBD1 has only two cysteine residues, which can exist as free thiol groups (reduced), as a disulphide bond (oxidized) or bound to a metal ion [e.g. Cu(I)-MBD1]. These three MBD1 forms have been investigated using CD. No major spectral change was seen between the different MBD1 forms, indicating that the folding is not changed upon metal binding. A copper-bound MBD1 was also studied by EPR, and the lack of an EPR signal suggests that the oxidation state of copper bound to MBD1 is Cu(I). Cu(I) binding studies were performed by equilibrium dialysis and revealed a stoichiometry of 1 : 1 and an apparent Kd = 46 microM. Oxidized MBD1, however, is not able to bind copper. Different copper complexes were investigated for their ability to reconstitute apo-MBD1. Given the same total copper concentration CuCl43- was superior to Cu(I)-thiourea (structural analogue of metallothionein) and Cu(I)-glutathione (used at fivefold higher copper concentration) although the latter two were able to partially reconstitute apo-MBD1. Cu(II) was not able to reconstitute apo-MBD1, presumably due to Cu(II)-induced oxidation of the thiol groups. Based on our results, glutathione and/or metallothionein are likely candidates for the in vivo incorporation of copper to Menkes protein.

Mutation spectrum of ATP7A, the gene defective in Menkes disease

Our knowledge about Menkes disease (MD) has expanded greatly since its description in 1962 as a new X-linked recessive neurodegenerative disorder of early infancy. Ten years later a defect in copper metabolism was established as the underlying biochemical deficiency. In the beginning of 1990s efforts were concentrated on the molecular genetic aspects. The disease locus was mapped to Xq13.3 and the gene has been isolated by means of positional cloning. This was the beginning of a series of new findings which have greatly enhanced our understanding of copper metabolism not only in human, but also in other species. This review will focus on the molecular genetic aspects of Menkes disease and its allelic form occipital horn syndrome. The mutations will be compared briefly with those described in the animal model mottled mouse, and in Wilson disease, the autosomal recessive disorder of copper metabolism.

Molecular cytogenetic detection of 9q34 breakpoints associated with nail patella syndrome

The nail patella syndrome (NPS1) is an autosomal dominant disorder characterised by dysplasia of the finger nails and skeletal abnormalities. NPS1 has been mapped to 9q34, to a 1 cM interval between D9S315 and the adenylate kinase gene (AK1). We have mapped the breakpoints within the candidate NPS1 region in two unrelated patients with balanced translocations. One patient [46,XY,t(1;9)(q32.1;q34)] was detected during a systematic survey of old cytogenetic files in Denmark and southern Sweden. The other patient [46,XY,t(9;17)(q34.1;q25)] was reported previously. D9S315 and AK1 were used to isolate YACs, from which endclones were used to isolate PACs. Two overlapping PAC clones span the 9q34 breakpoints in both patients, suggesting that NPS1 is caused by haploinsufficiency due to truncation or otherwise inactivation of a gene at or in the vicinity of the breakpoints.

Lethal neonatal Menkes' disease with severe vasculopathy and fractures

A male neonate presented with an acute onset of severe intra-abdominal bleeding, haemorrhagic shock and multiple fractures leading to death on d 27. Menkes' disease was diagnosed at autopsy and confirmed by copper accumulation studies on cultured fibroblasts. Such an early onset of fatal complications in this condition has not been previously reported. New insights into the pathogenesis of Menkes' disease provided by DNA mutation analysis and difficulties in neonatal diagnosis are discussed. Menkes' disease should be considered in male infants with pathological fractures and other signs of connective tissue disease, even in the neonatal period.

Menkes disease: underlying genetic defect and new diagnostic possibilities

Cloning of the gene defective in the X-linked neurodegenerative disorder Menkes disease led to a cascade of new findings. Besides giving a better understanding of the intracellular copper homeostasis, these findings had important consequences from a clinical point of view. Today the underlying genetic defect has been described in several patients affected by one of the three hereditary disorders of copper metabolism: Menkes disease, occipital horn syndrome and wilson disease. In this review we discuss mainly Menkes disease and the impact of the recent findings on the diagnosis of this disorder.

Not para-, not peri-, but centric inversion of chromosome 12

A 39 year old male with primary infertility was diagnosed as having Klinefelter syndrome by conventional cytogenetic analysis, which also showed an abnormal chromosome 12. Fluorescence in situ hybridisation (FISH) analysis of the aberrant chromosome using a 12 specific centromeric probe showed a break in the alphoid repeats followed by an inversion within the short arm, resulting in a pseudodicentric chromosome. Further FISH analyses using telomeric and subtelomeric probes showed that the other breakpoint was in the subtelomeric region of the short arm. The karyotype is designated 47,XXY,inv(12)(p10p13.3). To our knowledge this is the first report of a case of "centric inversion".

Turkish population data on the short tandem repeat locus TPOX

Allele and genotype frequencies were determined for the STR (short tandem repeat) locus TPOX in a random Turkish population sample of 200 individuals.

Early treatment of Menkes disease with parenteral copper-histidine: long-term follow-up of four treated patients

We report on the long-term clinical course of 4 boys with Menkes disease, treated from early infancy with parenteral copper-histidine, with follow-up over 10-20 years. Three of the 4 had male relatives with a severe clinical course compatible with classical Menkes disease. As a consequence of early treatment, our patients have normal or near-normal intellectual development, but have developed many of the more severe somatic abnormalities of the related disorder, occipital horn syndrome, including severe orthostatic hypotension in 2. In addition, 1 boy developed a previously unreported anomaly, namely, massive splenomegaly and hypersplenism as a consequence of a splenic artery aneurysm. Previously reported molecular studies in 2 of these patients had shown gene defects which would have predicted a truncated and probably nonfunctional gene product. Despite the favorable effects on the neurological symptoms, parenteral copper treatment for Menkes disease should still be regarded as experimental. The development of more effective treatments must await a more precise delineation of the role which the Menkes protein plays in intracellular copper trafficking.

Characterization of a supernumerary small marker X chromosome in two females with similar phenotypes

We describe two female patients mosaic for a cell line with an extra marker X chromosome in addition to a normal 46,XX cell line. To our knowledge, these cases are the first reports of females who had a cell line with a supernumerary marker X chromosome in addition to a normal cell line. They also had strikingly similar manifestations, including small hands and feet, minor facial anomalies, obesity, and mental retardation. The DNA content of the mar(X) chromosomes was investigated by fluorescent in situ hybridization using pericentromeric probes. The XIST gene, which is necessary for initiation of X-inactivation, was deleted from both marker chromosomes, suggesting that these chromosomes were not subject to inactivation. The short arm breakpoints of the mar(X)s were between the DNA markers DXS423E on Xp11.21 and UBE1 on Xp11.23. In Patient 1, mar(X) contained the androgen receptor gene and the DNA marker DXS1, both mapping to Xq11.2, whereas in Patient 2 the chromosome breakpoint was proximal to these markers. We suggest that the similar phenotypes of these patients may be due to the overexpression of genes in the common pericentromeric region of the X chromosome.

Genetic anticipation in Behçet's syndrome

OBJECTIVE

To examine the presence of genetic anticipation in families with Behçet's syndrome (BS).

METHODS

A total of 18 families with 40 affected members in two successive generations were evaluated by interviewing them for their ages at the onset of the first symptom of BS and for their ages at the time they fulfilled the diagnostic criteria.

RESULTS

It was noted that the age of onset of the first symptom was lower in the second generation in 14 families (p = 0.01) with a mean (SD) age of 20.57 (7.47) years in the children compared with 33.29 (9.92) years in the parents (t = 7.79, p < 0.0001), whereas the diagnostic criteria were fulfilled at an earlier age in the children in 15 families (p = 0.01) with a mean age of 21.2 (6.74) years in the children compared with 36.4 (9.55) years in the parents (t = 7.41, p < 0.0001).

CONCLUSION

Genetic anticipation was present in 15 of 18 (84%) of the families with BS in the form of earlier disease onset in the children compared with their parents.

Menkes disease: recent advances and new aspects

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Identification of point mutations in 41 unrelated patients affected with Menkes disease

Genomic DNA of 41 unrelated patients affected with the classical severe form of Menkes disease was investigated for point mutations in the ATP7A gene (previously designated as the "MNK" gene). Using SSCP analysis and direct sequencing of the exons amplified by PCR, we identified 41 different mutations, including 19 insertions/deletions, 10 nonsense mutations, 4 missense mutations, and 8 splice-site alterations. Approximately 90% of the mutations were predicted to result in the truncation of the protein (ATP7A). In 20 patients the mutations were within exons 7-10, and half of these mutations affected exon 8. Furthermore, five alterations were observed within the 6-bp sequence at the splice-donor site of intron 8, which would be predicted to affect the efficiency of splicing of exon 8. Although a specific function has not been attributed to the protein region encoded by this exon, this region may be important in serving as a "stalk" joining the metal-binding domains and the ATPase core. The present findings not only help us in understanding the underlying genetic defect but are invaluable data especially for carrier detection and prenatal diagnosis of this lethal disorder.

Menkes disease: recent advances and new insights into copper metabolism

Copper is a trace element necessary for the normal function of several important enzymes but copper homeostasis is still poorly understood. In recent years remarkable progress has been made in this field following the isolation of the gene defective in Menkes disease. Menkes disease and occipital horn syndrome are X-linked recessive disorders, demonstrating the vital importance of copper, which is also highly toxic in excessive amounts. Its destructive effects are reflected in the autosomal recessive Wilson's disease. Progressive neurodegeneration and connective tissue disturbances are the main manifestations of Menkes disease. Although many patients present a severe clinical course, variable forms can be distinguished, and the occipital horn syndrome has been suggested to be a mild allelic form. The Menkes locus is mapped to Xq13.3 and the gene defective in Menkes disease has been isolated by positional cloning. The gene is predicted to encode an energy-dependent copper-binding protein, the first intracellular copper transporter described in eukaryotes. Isolation of the gene and subsequent characterization of the exon-intron organization now enables the establishment of DNA-based diagnostic methods. Furthermore, identification of the Menkes disease gene led to other important findings, such as isolation of its mouse homologue, confirming the allelic relationship between Menkes disease and occipital horn syndrome, and isolation of the defective genes in Wilson's disease and its rat homologue.

A small supernumerary marker chromosome X identified by in situ hybridization

Cytogenetic analysis of a girl with moderate mental retardation and dysmorphic features revealed a 46,XX/47,XX,+mar karyotype. Fluorescence in situ hybridization using chromosome specific alpha satellite probes showed that the supernumerary marker originated from the X chromosome. To our knowledge, this is the first reported case of a female patient mosaic for a supernumerary small marker chromosome derived from X, and hence mosaic for trisomy of the pericentric region of the X chromosome.