Lieve Nuytinck

Diverse mutations in the gene for cartilage oligomeric matrix protein in the pseudoachondroplasia-multiple epiphyseal dysplasia disease spectrum.

Pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED) are autosomal dominant osteochondrodysplasias that result in mild to severe short-limb dwarfism and early-onset osteoarthrosis. PSACH and some forms of MED result from mutations in the gene for cartilage oligomeric matrix protein (COMP; OMIM 600310 [http://www3.ncbi.nlm. nih.gov:80/htbin-post/Omim/dispmim?600310]). We report the identification of COMP mutations in an additional 14 families with PSACH or MED phenotypes. Mutations predicted to result in single-amino acid deletions or substitutions, all in the region of the COMP gene encoding the calmodulin-like repeat elements, were identified in patients with moderate to severe PSACH. We also identified within this domain a missense mutation that produced MED Fairbank. In two families, one with mild PSACH and the second with a form of MED, we identified different substitutions for a residue in the carboxyl-terminal globular region of COMP. Both the clinical presentations of these two families and the identification of COMP-gene mutations provide evidence of phenotypic overlap between PSACH and MED. These data also reveal a role for the carboxyl-terminal domain in the structure and/or function of COMP.

Classical Ehlers-Danlos syndrome caused by a mutation in type I collagen

Classical Ehlers-Danlos syndrome (EDS) is characterized by skin hyperelasticity, joint hypermobility, increased tendency to bruise, and abnormal scarring. Mutations in type V collagen, a regulator of type I collagen fibrillogenesis, have been shown to underlie this type of EDS. However, to date, mutations have been found in only a limited number of patients, which suggests genetic heterogeneity. In this article, we report two unrelated patients with typical features of classical EDS, including excessive skin fragility, in whom we found an identical arginine-->cysteine substitution in type I collagen, localized at position 134 of the alpha1(I) collagen chain. The arginine residue is highly conserved and localized in the X position of the Gly-X-Y triplet. As a consequence, intermolecular disulfide bridges are formed, resulting in type I collagen aggregates, which are retained in the cells. Whereas substitutions of glycine residues in type I collagen invariably result in osteogenesis imperfecta, substitutions of nonglycine residues in type I collagen have not yet been associated with a human disease. In contrast, arginine-->cysteine substitutions in type II collagen have been identified in a variety of chondrodysplasias. Our findings show that mutations in other fibrillar collagens can be causally involved in classical EDS and point to genetic heterogeneity of this disorder.

Report of five novel and one recurrent COL2A1 mutations with analysis of genotype-phenotype correlation in patients with a lethal type II collagen disorder.

Achondrogenesis II-hypochondrogenesis and severe spondyloepiphyseal dysplasia congenita (SEDC) are lethal forms of dwarfism caused by dominant mutations in the type II collagen gene (COL2A1). To identify the underlying defect in seven cases with this group of conditions, we used the combined strategy of cartilage protein analysis andCOL2A1 mutation analysis. Overmodified type II collagen and the presence of type I collagen was found in the cartilage matrix of all seven cases. Five patients were heterozygous for a nucleotide change that predicted a glycine substitution in the triple helical domain (G313S, G517V, G571A, G910C, G943S). In all five cases, analysis of cartilage type II collagen suggested incorporation of the abnormal α1(II) chain in the extracellular collagen trimers. The G943S mutation has been reported previously in another unrelated patient with a strikingly similar phenotype, illustrating the possible specific effect of the mutation. The radiographically less severely affected patient was heterozygous for a 4 bp deletion in the splice donor site of intron 35, likely to result in aberrant splicing. One case was shown to be heterozygous for a single nucleotide change predicted to result in a T1191N substitution in the carboxy-propeptide of the proα1(II) collagen chain. Study of the clinical, radiographic, and morphological features of the seven cases supports evidence for a phenotypic continuum between achondrogenesis II-hypochondrogenesis and lethal SEDC and suggests a relationship between the amount of type I collagen in the cartilage and the severity of the phenotype.

Extremes of L-ficolin concentration in children with recurrent infections are associated with single nucleotide polymorphisms in the FCN2 gene.

l‐ficolin (also called ficolin‐2, P35 or hucolin) is a soluble pattern recognition molecule of suspected importance in anti‐microbial immunity. It activates the lectin pathway of complement and acts as an opsonin. l‐ficolin, encoded by the FCN2 gene, recognizes microbial polysaccharides and glycoconjugates rich in GlcNAc or GalNAc. We report here data concerning four single nucleotide polymorphisms (SNPs) of the FCN2 gene and their relationship to l‐ficolin serum concentrations. There are two pairs of SNPs in linkage disequilibrium: ss32469536 (located in promoter) with rs7851696 (in exon 8) and ss32469537 (promoter) with ss32469544 (exon 8). We selected groups possessing low or high serum l‐ficolin concentrations (≤ 2·8 µg/ml or ≥ 4·5 µg/ml, respectively) from Polish children suffering from recurrent respiratory infections (n = 146). Low l‐ficolin levels were associated with variant alleles for ss32469536 and rs7851696 and normal alleles for ss32469537 and ss32469544. Conversely, high l‐ficolin levels were associated with variant alleles of ss32469537 and ss32469544. FCN2 genotyping should be a valuable additional tool for disease association studies.

Clinical and radiographic features of a family with hypochondroplasia owing to a novel Asn540Ser mutation in the fibroblast growth factor receptor 3 gene

Editor—Hypochondroplasia is a mild, autosomal dominant skeletal dysplasia. The relative dearth of specific clinical manifestations and the absence of pathognomonic radiographic features often make the diagnosis of hypochondroplasia difficult.1-4 Short limbed dwarfism is rarely recognised before the age of 2 years and is usually mild with heights up to the low normal range. Muscular body build, macrocephaly with mild frontal bossing, and lumbar hyperlordosis are frequently reported. The radiographic features are variable and can be almost normal in mildly affected subjects.4 They most typically include no change or decrease in the interpedicular distance from the first to the fifth lumbar vertebral bodies, anteroposterior shortening of the lumbar pedicles, short iliac bones with flat acetabular roof, small sacrosciatic notches, short tubular bones, short and broad femoral necks, and relative elongation of the distal or proximal portion of the fibula.2 4 Proof that achondroplasia and hypochondroplasia are allelic disorders came with the discovery that both conditions map to the distal short arm of chromosome 4.5 6 Subsequently, mutation analysis of the FGFR3 gene, located in the 4p16.3 region, showed a recurrent mutation (N540K) in several unrelated hypochondroplasia patients.7 8 Recently, two novel mutations in the same region of the FGFR3 gene causing hypochondroplasia have been identified: N540T in a Dutch family and I538V in a Swedish kindred.9 10 In some sporadic patients and …

Gene polymorphisms of Toll-like and related recognition receptors in relation to the vaginal carriage of Gardnerella vaginalis and Atopobium vaginae.

Host genetic factors have previously been found to act as determinants of differential susceptibility to major infectious diseases. It is less clear whether such polymorphisms may also impose on pathogen recognition in mucosal overgrowth conditions such as bacterial vaginosis, an anaerobic overgrowth condition characterised by the presence of a vaginal biofilm consisting of the Gram-positive anaerobes Gardnerella vaginalis and Atopobium vaginae. We selected 34 single nucleotide polymorphisms pertaining to 9 genes involved with Toll-like receptor-mediated pathogen recognition and/or regulation (LBP, CD14, TLR1, TLR2, TLR4, TLR6, MD2, CARD15 and SIGIRR) and assessed in a nested case-control study their putative association with bacterial vaginosis, as diagnosed by Gram staining, and with the vaginal carriage of A. vaginae and G. vaginalis, as determined by species-specific PCR, among 144 pregnant women. Carriage of G. vaginalis during early pregnancy was associated with the -1155A>G substitution in the promoter region of the MD2 gene (p=0.041). The presence of A. vaginae during the first half of the pregnancy was significantly associated with the CD14 intron 2 1342G>T (p=0.039), the TLR1 exon 4 743A>G (p=0.038), and the CARD15 exon 4 14772A>T (p=0.012) polymorphisms, and marginally significantly associated with the LBP exon13 26842C>T (p=0.056), the CD14 promoter -260C>T (p=0.052), and the TLR1 promoter -7202A>G (p=0.062) polymorphisms. However, no association between gene polymorphisms and bacterial vaginosis as such could be documented. Our data suggest that some degree of genetic susceptibility involving pathogen recognition may occur with the key bacterial vaginosis organism, A. vaginae.

Homozygosity by descent for a COL1A2 mutation in two sibs with severe osteogenesis imperfecta and mild clinical expression in the heterozygotes

Abstract We report two sibs with severe, progressively deforming osteogenesis imperfecta (OI) and homozygosity by descent for a glycine 751 to serine substitution in the α2(I) collagen chain due to a G to A transition in the COL1A2 gene. The parents, who were first cousins, and two elder sibs were heterozygous for the mutation and presented mild clinical manifestations of OI. Collagen studies on cultured fibroblasts from one of the probands and from the father showed that cells from the homozygote produced only mutant, unstable collagen I, whereas cells from the heterozygote produced both normal and mutant collagen I. This family represents an exceptional example of autosomal recessive OI, caused by homozygosity for a missense mutation in collagen I.

Substitution of glycine-661 by serine in the alpha1(I) and alpha2(I) chains of type I collagen results in different clinical and biochemical phenotypes.

We have characterised a point mutation causing the substitution of serine for glycine at position 661 of the α1(I) chain of type I collagen in a child with a severe form of osteogenesis imperfecta. An identical glycine substitution in the α2(I) chain was previously detected in a woman with post-menopausal osteoporosis. Two of her sons were heterozygous for the mutation and the third son was homozygous as a result of uniparental isodisomy. Biochemical profiles of the type I collagen heterotrimers were studied in each of the patients and compared with a control. Medium and cell-layer collagens were overmodified in all patients. Overmodification was obvious in the patient with the α1(I) mutation but mild in the patients with the α2(I) mutation, being slightly less evident in the heterozygote than in the homozygote. Investigation of the melting curves of the mutant collagen trimers in all three patients showed the same slight decrease in thermal stability and, hence, a lack of correlation with phenotypic severity. In contrast, the degree of overmodification of the collagen alpha chains was correlated with the phenotypic severity. The clinical observations in these patients illustrate the possibly predominant role of mutations in the collagen α1(I) chains over the same mutations in the α2(I) chains in determining the clinical outcome.

An interstitial deletion of chromosome 7 at band q21: A case report and review

We report on a girl with moderate developmental delay and mild dysmorphic features. Cytogenetic investigations revealed a de novo interstitial deletion at the proximal dark band on the long arm of chromosome 7 (7q21.1‐q21.3) in all analyzed G‐banded metaphases of lymphocytes and fibroblasts. Fluorescence in situ hybridization (FISH) and molecular studies defined the breakpoints at 7q21.11 and 7q21.3 on the paternal chromosome 7, with the proximal deletion breakpoint between the elastin gene (localized at 7q11.23) and D7S2517, and the distal breakpoint between D7S652 and the COL1A2 gene (localized at 7q21.3‐q22.1). Deletions of interstitial segments at the proximal long arm of chromosome 7 at q21 are relatively rare. The karyotype–phenotype correlation of these patients is reviewed and discussed. The clinical findings of patients with a deletion at 7q21 significantly overlap with those of patients with maternal uniparental disomy of chromosome 7 (matUPD(7)) and Silver–Russell syndrome (SRS, OMIM 180860). Therefore, 7q21 might be considered a candidate chromosomal region for matUPD(7) and SRS.

Acanthosis nigricans in a child with mild osteochondrodysplasia and K650Q mutation in the FGFR3 gene

A girl with a mild sporadic osteochondrodysplasia (OCD) similar to hypochondroplasia but with significant short stature is reported. She has been followed clinically between the ages of 9 months and 14 years. Growth remained normal throughout childhood with stature evolving about 3.5 SDs under the mean for age. By 8 years of age gradually appearing acanthosis nigricans (AN) in the neck and flanks was histopathologically confirmed. It provided the new incentive to search for specific FGFR3 mutations associated with this dermatologic abnormality. This resulted in the identification of the 1948A > C transversion predicting the K650Q missense substitution in the FGFR3 protein. Besides the expansion of the phenotypic spectrum of FGFR3‐related OCDs to HCH with AN, this observation underscores the continuing adverse effect of this specific mutation upon the normal inhibitory signaling of the receptor at least in epidermal cells.