Mosaic ACVRL1 and ENG mutations in hereditary haemorrhagic telangiectasia patients.

Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant disorder caused by mutations in the ACVRL1, ENG, and SMAD4 genes. HHT is commonly characterised by small arteriovenous malformations (AVMs) known as telangiectasias of the skin, oral or gastrointestinal mucosa, as well as larger AVMs of solid organs (lungs, liver, brain). However, the manifestations of HHT are extremely variable. Two patients with no family history of HHT and strikingly different clinical presentations, who are mosaic for mutations in the ACVRL1 or ENG gene, are reported here. These cases represent the first report of mosaicism in patients clinically affected with classical HHT and pulmonary arterial hypertension, and suggest the need for awareness of mosaicism when performing clinical testing for this disorder.

A novel X-linked multiple congenital anomaly syndrome associated with an EBP mutation.

Mutations of the gene coding for emopamil binding protein (EBP) can lead to deficient activity of 3-ß-hydroxysteroid Δ(8), Δ(7) isomerase and are most commonly identified in. association with the X-linked dominant (male lethal) chondrodysplasia punctata (CDPX2), also known as Conradi-Hunermann syndrome. Our group has identified a hemizygous EBP mutation in males with a phenotype remarkable for Dandy-Walker malformation, cataracts, collodion skin and cryptorchidism. Additional findings of hydrocephalus, dysplasia of the corpus callosum, cardiovascular, craniofacial and skeletal anomalies were regularly seen in affected males and the family histories were supportive of an X-linked -recessive condition. The regularly reproducible constellation of cardinal features aligns very nicely with other disorders of sterol biosynthesis and is further distinguished by an absence of arty clinical manifestations in obligate carrier females. Biochemical analysis of blood from cases demonstrated markedly increased levels of 8(9)-cholestenol, and 8-dehydroeholesterol and a mildly increased level of 7-dehydrocholesterol; a similar pattern to what is seen in CDPX2. Sequence analysis of EJJP revealed a novel hemizygous missense mutation at position 141, predictive of a tryptophan to cysteine substitution (c.141G>T, p.W47C). The unaffected mothers were heterozygous for the c.141G>T mutation arid showed random X-inactivation pattern upon.

Major histocompatibility complex heterozygosity reduces fitness in experimentally infected mice.

It is often suggested that heterozygosity at major histocompatibility complex (MHC) loci confers enhanced resistance to infectious diseases (heterozygote advantage, HA, hypothesis), and overdominant selection should contribute to the evolution of these highly polymorphic genes. The evidence for the HA hypothesis is mixed and mainly from laboratory studies on inbred congenic mice, leaving the importance of MHC heterozygosity for natural populations unclear. We tested the HA hypothesis by infecting mice, produced by crossbreeding congenic C57BL/10 with wild ones, with different strains of Salmonella, both in laboratory and in large population enclosures. In the laboratory, we found that MHC influenced resistance, despite interacting wild-derived background loci. Surprisingly, resistance was mostly recessive rather than dominant, unlike in most inbred mouse strains, and it was never overdominant. In the enclosures, heterozygotes did not show better resistance, survival, or reproductive success compared to homozygotes. On the contrary, infected heterozygous females produced significantly fewer pups than homozygotes. Our results show that MHC effects are not masked on an outbred genetic background, and that MHC heterozygosity provides no immunological benefits when resistance is recessive, and can actually reduce fitness. These findings challenge the HA hypothesis and emphasize the need for studies on wild, genetically diverse species.

Unlabeled oligonucleotides as internal temperature controls for genotyping by amplicon melting.

Amplicon melting is a closed-tube method for genotyping that does not require probes, real-time analysis, or allele-specific polymerase chain reaction. However, correct differentiation of homozygous mutant and wild-type samples by melting temperature (Tm) requires high-resolution melting and closely controlled reaction conditions. When three different DNA extraction methods were used to isolate DNA from whole blood, amplicon Tm differences of 0.03 to 0.39 degrees C attributable to the extractions were observed. To correct for solution chemistry differences between samples, complementary unlabeled oligonucleotides were included as internal temperature controls to shift and scale the temperature axis of derivative melting plots. This adjustment was applied to a duplex amplicon melting assay for the methylenetetrahydrofolate reductase variants 1298A>C and 677C>T. High- and low-temperature controls bracketing the amplicon melting region decreased the Tm SD within homozygous genotypes by 47 to 82%. The amplicon melting assay was 100% concordant to an adjacent hybridization probe (HybProbe) melting assay when temperature controls were included, whereas a 3% error rate was observed without temperature correction. In conclusion, internal temperature controls increase the accuracy of genotyping by high-resolution amplicon melting and should also improve results on lower resolution instruments.

Multiplex genotyping by melting analysis of loci-spanning probes: beta-globin as an example.

Multiplexing genotyping technologies usually require as many probes as genetic variants. Oligonucleotides that span multiple loci--loci spanning probes (LSProbes)--hybridize to two or more noncontiguous DNA sequences present in a template and can be used to analyze multiple variants simultaneously. The intervening template sequence, omitted in the LSProbe, creates a bulge-loop during binding. Melting temperatures of the probe, monitored by fluorescence reading are specific to the presence or absence of the mutations. We previously described LSProbes as a molecular haplotyping tool and apply here the principle to genotype simultaneously three mutations of the beta-globin gene responsible for the corresponding hemoglobinopathies. Analysis with both labeled and unlabeled LSProbes demonstrate that the four possible alleles studied (WT, HbS, HbC, and HbE) are identifiable by the specific melting temperatures of the LSProbes. This demonstrates that, in addition to their haplotyping capabilities, LSProbes are able to genotype in a single step, loci 58 nucleotides apart.

Infection-dependent phenotypes in MHC-congenic mice are not due to MHC: can we trust congenic animals?

BACKGROUND: Congenic strains of mice are assumed to differ only at a single gene or region of the genome. These mice have great importance in evaluating the function of genes. However, their utility depends on the maintenance of this true congenic nature. Although, accumulating evidence suggests that congenic strains suffer genetic divergence that could compromise interpretation of experimental results, this problem is usually ignored. During coinfection studies with Salmonella typhimurium and Theiler's murine encephalomyelitis virus (TMEV) in major histocompatibility complex (MHC)-congenic mice, we conducted the proper F2 controls and discovered significant differences between these F2 animals and MHC-genotype-matched P0 and F1 animals in weight gain and pathogen load. To systematically evaluate the apparent non-MHC differences in these mice, we infected all three generations (P0, F1 and F2) for 5 MHC genotypes (b/b, b/q and q/q as well as d/d, d/q, and q/q) with Salmonella and TMEV. RESULTS: Infected P0 MHC q/q congenic homozygotes lost significantly more weight (p = 0.02) and had significantly higher Salmonella (p < 0.01) and TMEV (p = 0.02) titers than the infected F2 q/q homozygotes. Neither weight nor pathogen load differences were present in sham-infected controls. CONCLUSIONS: These data suggest that these strains differ for genes other than those in the MHC congenic region. The most likely explanation is that deleterious recessive mutations affecting response to infection have accumulated in the more than 40 years that this B10.Q-H-2q MHC-congenic strain has been separated from its B10-H-2b parental strain. During typical experiments with congenic strains, the phenotypes of these accumulated mutations will be falsely ascribed to the congenic gene(s). This problem likely affects any strains separated for appreciable time and while usually ignored, can be avoided with the use of F2 segregants.

Mosaicism in Stickler syndrome.

Stickler syndrome is a heterogeneous condition due to mutations in COL2A1, COL11A1, COL11A2, and COL9A1. To our knowledge, neither non-penetrance nor mosaicism for COL2A1 mutations has been reported for Stickler syndrome. We report on a family with two clinically affected sibs with Stickler syndrome who have clinically unaffected parents. Both sibs have a novel heterozygous mutation in exon 26 of COL2A1 (c.1525delT); this results in a premature termination codon downstream of the mutation site. One parent was found to have low level mosaicism in DNA extracted from whole blood. This scenario encourages consideration of molecular testing in seemingly unaffected parents for recurrence risks and potential screening for mild age-related manifestations.

p.R672C mutation of MYH3 gene in an Egyptian infant presented with Freeman-Sheldon syndrome.

OBJECTIVE: To define the mutation type in a clinically suspected Egyptian child with Freeman-Sheldon syndrome (FSS); it involves certain skeletal malformations with some facial characteristics; skeletal malformations include camptodactyly with ulnar deviation, talipes equinovarus, while the facial characteristics include deep-sunken eyes with hypertelorism, long philtrum, small pinched nose and pursed mouth. METHODS: Amplification of exon 17 of the embryonic myosin heavy chain (MYH3) gene was done using one forward and two different reverse primers, and then the cleaned PCR product was sequenced. RESULT: A de novo missense mutation (c.2014C>T with replacement C > Y) in MYH3 gene leading to change of arginine at position 672 by cytosine in protein sequence. CONCLUSION: Mutation analysis remains to be the standard way for definitive diagnosis in FSS. The authors currently report, for the first time in an Egyptian infant aged 16 months who presented with FSS, a c.2014C>T missense mutation of MYH3 gene, with no family history or consanguinity.

5'UTR mutations of ENG cause hereditary hemorrhagic telangiectasia.

BACKGROUND: Hereditary hemorrhagic telangiectasia (HHT) is a vascular disorder characterized by epistaxis, arteriovenous malformations, and telangiectases. The majority of the patients have a mutation in the coding region of the activin A receptor type II-like 1 (ACVRL1) or Endoglin (ENG) gene. However, in approximately 15% of cases, sequencing analysis and deletion/duplication testing fail to identify mutations in the coding regions of these genes. Knowing its vital role in transcription and translation control, we were prompted to investigate the 5'untranslated region (UTR) of ENG. METHODS AND RESULTS: We sequenced the 5'UTR of ENG for 154 HHT patients without mutations in ENG or ACVRL1 coding regions. We found a mutation (c.-127C > T), which is predicted to affect translation initiation and alter the reading frame of endoglin. This mutation was found in a family with linkage to the ENG, as well as in three other patients, one of which had an affected sibling with the same mutation. In vitro expression studies showed that a construct with the c.-127C > T mutation alters the translation and decreases the level of the endoglin protein. In addition, a c.-9G > A mutation was found in three patients, one of whom was homozygous for this mutation. Expression studies showed decreased protein levels suggesting that the c.-9G > A is a hypomorphic mutation. CONCLUSIONS: Our results emphasize the need for the inclusion of the 5'UTR region of ENG in clinical testing for HHT.

MHC heterozygosity confers a selective advantage against multiple-strain infections.

Genetic heterozygosity is thought to enhance resistance of hosts to infectious diseases, but few tests of this idea exist. In particular, heterozygosity at the MHC, the highly polymorphic loci that control immunological recognition of pathogens, is suspected to confer a selective advantage by enhancing resistance to infectious diseases (the "heterozygote advantage" hypothesis). To test this hypothesis, we released mice into large population enclosures and challenged them with multiple strains of Salmonella and one of Listeria. We found that during Salmonella infections with three avirulent strains, MHC heterozygotes had greater survival and weight than homozygotes (unlike sham controls), and they were more likely to clear chronic Salmonella infection than homozygotes. In laboratory experiments, we found that MHC heterozygosity enhanced the clearance of multiple-strain Salmonella infections. Yet, contrary to what is widely assumed, the benefits of heterozygosity were due to resistance being dominant rather than overdominant, i.e., heterozygotes were more resistant than the average of parental homozygotes, but they were not more resistant than both. The fact that MHC heterozygotes were more resistant to infection and had higher fitness than homozygotes provides a functional explanation for MHC-disassortative mating preferences.