Mutation of DNAJC19, a human homologue of yeast inner mitochondrial membrane co-chaperones, causes DCMA syndrome, a novel autosomal recessive Barth syndrome-like condition.

BACKGROUND: A novel autosomal recessive condition, dilated cardiomyopathy with ataxia (DCMA) syndrome, has been identified in the Canadian Dariusleut Hutterite population, characterised by early onset dilated cardiomyopathy with conduction defects, non-progressive cerebellar ataxia, testicular dysgenesis, growth failure, and 3-methylglutaconic aciduria. OBJECTIVE: To map DCMA syndrome and identify the mutation underlying this condition. METHODS: A genome wide scan was undertaken on consanguineous Hutterite families using a homozygosity mapping approach in order to identify the DCMA associated chromosomal region. Mutation analysis was carried out on positional candidate genes in this region by sequencing. Reverse transcriptase polymerase chain reaction and bioinformatics analyses were then used to characterise the mutation and determine its effect on the protein product. RESULTS: The association of DCMA syndrome with a 2.2 Mb region of chromosome 3q26.33 was found. A disease associated mutation was identified: IVS3-1 G-->C in the DNAJC19 gene, encoding a DNAJ domain containing protein of previously unknown function (Entrez Gene ID 131118). CONCLUSIONS: The DNAJC19 protein was previously localised to the mitochondria in cardiac myocytes, and shares sequence and organisational similarity with proteins from several species including two yeast mitochondrial inner membrane proteins, Mdj2p and Tim14. Tim14 is a component of the yeast inner mitochondrial membrane presequence translocase, suggesting that the unique phenotype of DCMA may be the result of defective mitochondrial protein import. It is only the second human disorder caused by defects in this pathway that has been identified.

Effect of heterozygosity for the methionine synthase 2756 A-->G mutation on the risk for recurrent cardiovascular events.

Increased dietary intake of folate has been shown to significantly reduce the risk for fatal myocardial infarction, possibly by lowering homocysteine levels. We therefore investigated the association between recurrent cardiovascular events and a mutation in methionine synthase (2756 A-->G)--an enzyme directly involved in folate and homocysteine metabolism. This mutation significantly reduced the risk for recurrent cardiovascular events and elevated red blood cell folate levels.

Molecular diagnosis of the fragile X [Fra (X)] syndrome: calculation of risks based on flanking DNA markers in small phase-unknown families.

We studied two small, two-generation families with the fragile X [Fra (X)] syndrome. The absolute phase of the DNA markers in relation to the disease in the mother was not known in either family. We present the derivation of risks for these families using flanking markers, taking into account the uncertainty regarding maternal phase. Since the use of flanking markers fails to yield useful counseling data in the 1/3 to 1/7 of all cases where a single recombination event occurs between the two flanking markers, we calculate the probability that this method is likely to be successful or unsuccessful when prenatal diagnosis is attempted using linked RFLPs.

Maternal uniparental heterodisomy for chromosome 16: case report.

A patient with uniparental heterodisomy for chromosome 16 presented initially at prenatal diagnosis with a karyotype of 47, XX + 16 on chorionic villus sampling at 11 weeks gestation. The pregnancy was proceeding normally and follow up amniocentesis showed a normal female karyotype. At birth, the child was healthy, but had intrauterine growth retardation. She had unilateral talipes equinovarus and unilateral renal agenesis. Her growth had improved to within the normal range by age three years. On examination, she has epicanthic folds, a flat midface and almond shaped eyes. While these characteristics are not frankly abnormal, they are significantly different from other relatives in her family.

Carrier detection and prenatal diagnosis of Pelizaeus-Merzbacher disease using a combination of anonymous DNA polymorphisms and the proteolipid protein (PLP) gene cDNA.

We report carrier identification and a prenatal diagnosis using DNA polymorphisms in 2 families with X-linked Pelizaeus-Merzbacher disease (PMD). In both families, the proteolipid protein (PLP) gene in the single affected male could be traced back to his unaffected maternal grandfather. Therefore, each family contains a new mutation. In the case of the prenatal diagnosis, the fetus was shown by cytogenetic analysis to be a female, who we predict will be a noncarrier of PMD based on her genotype with the PLP intragenic polymorphism.

Large kindred with Ehlers-Danlos syndrome type IV due to a point mutation (G571S) in the COL3A1 gene of type III procollagen: low risk of pregnancy complications and unexpected longevity in some affected relatives.

Ehlers-Danlos syndrome (EDS) type IV is an autosomal dominant connective tissue disorder. Early morbidity and mortality results from rupture of vessels and internal organs. A large kindred with EDS type IV was studied clinically, and the biochemical defects and underlying mutation in the COL3A1 gene that encodes the chains of type III procollagen were identified. A G-->A transition results in a single amino acid substitution, G571S, in the triple helical domain of the products of one COL3A1 allele. Although the clinical findings seen on examination are characteristic of EDS type IV, longevity is longer than that seen in many families and there is less pregnancy-associated morbidity or mortality than in some families. This suggests that some clinical aspects of EDS type IV may be related to the nature of the mutation and its effect on the behavior of the protein.

Barth syndrome: clinical observations and genetic linkage studies.

Barth syndrome is an X-linked recessive condition characterized by skeletal myopathy, cardiomyopathy, proportionate short stature, and recurrent neutropenia, but with normal cognitive function. Some, but not all patients, exhibit carnitine deficiency and/or the presence of 3-methylglutaconic and ethylhydracylic acids in urine. Recently the mutation causing Barth syndrome was localised to the Xq28 region by linkage analysis. We report 6 cases of Barth syndrome from 4 families and highlight the fact that neuromuscular and cardiovascular symptoms and the severity of infections tend to improve with age, while short stature persists. Also previously unreported was myopathic facies and nasal quality to speech in our cases. The urinary organic acid abnormalities and plasma carnitine deficiency were inconsistent findings. We propose that they may be epiphenomena rather than indicators of the primary metabolic defect, and that the primary defect or defects in this disorder may lie in the mitochondrial electron transport chain.

Disseminated bacille Calmette-Guérin infection in an infant with a novel deletion in the interferon-gamma receptor gene.

Six weeks after receiving BCG vaccination, a Canadian aboriginal infant presented with suspected sepsis, lymphadenopathy and hepatosplenomegaly. Lymph node biopsy revealed macrophages filled with acid-fast bacilli. Mycobacterium bovis was cultured from tissue specimens and there was evidence of concomitant cytomegalovirus disease. The infant died of disseminated BCG infection. A novel deletion at nucleotide 165 in the interferon-gamma receptor (IFN-gammaR1) was identified. The incidence of this mutation in the aboriginal population and the impact on the heterozygous state are unknown.

Cost analysis of DNA-based testing in a large Canadian family with multiple endocrine neoplasia type 2.

One of the major goals of genetic testing is the reduction of morbidity and mortality. Given the appropriate circumstances, this can result in reduction in health care costs. Such savings can be demonstrated most effectively in large families with mutations in well characterized, dominantly acting genes. In our large family, a point mutation TGC>CGC in exon 10 of the RET proto-oncogene, which results in a missense mutation (Cys620Arg), was identified in two individuals. The proband has medullary thyroid carcinoma (MTC), as did her deceased mother. One son has MTC and Hirschsprung's disease. The proband's mother had nine siblings; the proband has three siblings, another son, and 69 maternal cousins. Genetic testing has been performed on the closest relatives and has identified four individuals with, and 54 individuals without, a familial RET mutation. Significant cost savings have been realized in both genetic testing and clinical surveillance. In this family, for every at-risk individual identified as a true-negative, the minimum yearly savings in clinical surveillance is 508 dollars per person. As demonstrated by this case, economic costs of genetic diagnostics should take into account the potential saved monies in tests, both molecular and clinical.

Correction of the published sequence for the human proteolipid protein gene.

In the human proteolipid protein gene, the base sequence of the intronic region 5' to exon 6 was found to be 5'-ctctttcattttcctgcag-3' and not 5'-ctctttt-cattttcctgcag-3' as previously reported.

An A to T transversion at position -5 of the factor IX promoter results in hemophilia B.

The molecular pathology that results in hemophilia B has been determined by many studies to be highly variable. Several point mutations have been identified in a 40-bp region within the Factor IX promoter. These include mutations at nucleotides -20, -6, +8, and +13. Here we report an A to T transversion at position -5 of the Factor IX gene. There is strong circumstantial evidence to support an important role for this region of the Factor IX promoter in the developmental regulation of the gene through the binding of specific transcription factors.

Gonadal mosaicism in a family with adrenoleukodystrophy: molecular diagnosis of carrier status among daughters of a gonadal mosaic when direct detection of the mutation is not possible.

Adrenoleukodystrophy is a severe, X-linked neurological disease that has been shown to be linked to DNA markers from Xq28. We tested several families with these markers and, in one family, found two apparent recombination events between DXS52 and the disease. Expansion of the study to include other tests and several others markers from Xq28 led us to conclude that recombination probably had not occurred and that, instead, the mutation in this family had a mitotic origin and that the grandmother was a gonadal mosaic. For genes that have been cloned, it is often possible to demonstrate the presence or absence of a specific mutation in such families and to determine carrier status on that basis. This is not possible when the gene has not been cloned. We therefore describe a method that can be employed by a molecular diagnostic laboratory to discriminate between people who inherit the same RFLP haplotype, with or without the mutation, from a parent with gonadal mosaicism in diseases where direct gene analysis is not yet possible.

Cosegregation of von Willebrand factor gene polymorphisms and possible germinal mosaicism in type IIB von Willebrand disease.

Recent reports of the mutations resulting in von Willebrand disease (vWD) have indicated that some cases of type IIA vWD are caused by single nucleotide substitutions in the gene encoding von Willebrand factor (vWF). However, the molecular pathogenesis of type IIB vWD remains unresolved and, with the complex posttranslational processing required for fully functional vWF, the mutations responsible for this phenotype may occur at loci other than the vWF gene. This study has used six intragenic vWF polymorphisms to assess the linkage of type IIB vWD to this gene in three families (48 individuals). The results of these studies indicate that there is significant linkage between the vWF gene and the type IIB phenotype (logarithm of the odds ratio of 7.2 at theta = 0), suggesting that the mutations responsible for this disorder frequently occur at this locus. Results from one of these families indicates that the disorder has been transmitted from an unaffected parent to two children who have inherited the same vWF gene as seven unaffected siblings. This finding is suggestive of the presence of germinal mosaicism for the mutation in the father.

Genetic technologies, health care policy and the patent bargain.

The idea of granting patents on human genetic material continues to cause controversy. The debate is largely focussed on the moral acceptability of human gene patents, the impact of gene patents on the research environment and the value of patents to stimulate innovation and the commercialization and dissemination of genetic discoveries. As highlighted by a recent controversy in Canada, patents can also have a profound effect on health policy and access to genetic services. Creative and bold patent reform initiatives are necessary to ensure that society will, to the highest degree possible, reap the health care benefits of the genetic revolution.

Mutations causing hemophilia B: direct estimate of the underlying rates of spontaneous germ-line transitions, transversions, and deletions in a human gene.

Spontaneous mutation provides the substrate for evolution on one hand and for genetic susceptibility to disease on the other hand. X-linked diseases such as hemophilia B offer an opportunity to examine recent germ-line mutations in humans. By utilizing the direct sequencing method of genomic amplification with transcript sequencing, eight regions (2.46 kb) of likely functional significance in the factor IX gene have been sequenced in a total of 60 consecutive, unrelated hemophiliacs. The high frequency of patient ascertainment from three regions in the midwestern United States and Canada suggests that the sample is representative of hemophiliacs of northern European descent. Twenty-six of the delineated mutations are reported herein, and the group of 60 is analyzed as a whole. From the pattern of mutations causing disease and from a knowledge of evolutionarily conserved amino acids, it is possible to reconstruct the underlying pattern of mutation and to calculate the mutation rates per base pair per generation for transitions (27 x 10(-10)), transversions (4.1 x 10(-10), and deletions (0.9 x 10(-10)) for a total mutation rate of 32 x 10(-10). The proportion of transitions at non-CpG nucleotides is elevated sevenfold over that expected if one base substitution were as likely as another. At the dinucleotide CpG, transitions are elevated 24-fold relative to transitions at other sites. The pattern of spontaneous mutations in factor IX resembles that observed in Escherichia coli when the data are corrected for ascertainment bias. The aggregate data hint that most mutations may be due to endogenous processes. The following additional conclusions emerge from the data: (1) Although in recent decades reproductive fitness in individuals with mild and moderate hemophilia has been approximately normal, the large number of different mutations found strongly suggest that these levels of disease substantially compromised reproduction in previous centuries. (2) Mutations which putatively affect splicing account for at least 13% of independent mutations, indicating that the division of the gene into eight exons presents a significant genetic cost for the organism. In one individual a "silent" mutation at lysine 5 is likely to cause hemophilia by generating a perfect splice donor consensus sequence in exon b. (3) All the missense mutations occurred at evolutionarily conserved amino acids. As additional data are generated on the pattern of mutations caused by specific mutagens, it will be possible to utilize the pattern of spontaneous mutation to estimate the maximal contribution of that mutagen during the past century.

Further evidence for genetic heterogeneity in familial hemophagocytic lymphohistiocytosis (FHLH).

Familial hemophagocytic lymphohistiocytosis (FHLH; MIM #267700) is an autosomal recessive disorder of immune regulation characterized by fever, hepatosplenomegaly, and cytopenia that is fatal without bone marrow transplantation. Recent studies have suggested the existence of FHLH loci at 9q21.3-22 and t0q21-22 in Asian and European/African/Australian families, respectively. We studied two unrelated Canadian families in which first cousins were affected with FHLH. In an effort to localize the causative gene, we completed a genome-wide screen for homozygosity by descent by using an automated system to genotype 400 highly polymorphic dinucleotide repeat markers covering the genome with an average resolution of 10 centiMorgans (cM). We identified a total of three candidate loci that met the combined criteria for homozygosity by descent in one family and shared maternal alleles in the other family. One of these, D9S1690, had a cytogenetic localization (9q22.33) proximal to a previously reported inversion of chromosome 9 in an FHLH patient. However, additional closely linked flanking markers within 1-2 cM of all three candidates did not conform to the criteria for linkage in either family. Similarly, we excluded the linked 9q21.3-q22 and 10q21-22 regions recently reported in Asian and European/African/Australian families, respectively. The two families were then analyzed independently to encompass the possibility that they were segregating separate genes. Six additional candidate loci were identified on the basis of homozygosity for the same allele in all affected members of one family, but further analysis of closely linked flanking markers did not demonstrate similar homozygosity. Our data provide further evidence of genetic heterogeneity in FHLH and suggest the existence of at least a third locus for this disease.

Variation of the non-factor VIII sequences detected by a probe from intron 22 of the factor VIII gene.

A severe hemophilia A family has been studied with the factor VIII (F.VIII) intragenic XbaI polymorphism. During this investigation, a new variant hybridization pattern was observed with important implications concerning the non-F.VIII DNA sequences detected by the probe from intron 22, p482.6. Both Southern hybridization studies and direct analysis of amplified DNA demonstrated a variant form of the non-F.VIII sequences. This variant DNA sequence has not been responsible for any detectable phenotypic abnormalities, and likely represents a polymorphic change. In conclusion, this study has shown that the non-F.VIII sequences detected with the probe p482.6 are situated on the X chromosome, they seem to be present in two copies, and either or both copies infrequently possess a polymorphic XbaI site or a partial deletion.