Katja Hilbert

A specific collagen type II gene (COL2A1) mutation presenting as spondyloperipheral dysplasia

We report on a patient with a skeletal dysplasia characterized by short stature, spondylo-epiphyseal involvement, and brachydactyly E-like changes. This condition has been described as spondyloperipheral dysplasia and the few published cases suggest autosomal dominant inheritance with considerable clinical variability. We found our sporadic case to be due to a collagen type II defect resulting from a specific COL2A1 mutation. This mutation is the first to be located at the C-terminal outside the helical domain of COL2A1. A frameshift as consequence of a 5 bp duplication in exon 51 leads to a stop codon. The resulting truncated C-propeptide region seems to affect helix formation and produces changes of chondrocyte morphology, collagen type II fibril structure and cartilage matrix composition. Our case with its distinct phenotype adds another chondrodysplasia to the clinical spectrum of type II collagenopathies.

Dominant negative mutations in the C-propeptide of COL2A1 cause platyspondylic lethal skeletal dysplasia, Torrance type, and define a novel subfamily within the type 2 collagenopathies

Platyspondylic lethal skeletal dysplasia (PLSD) Torrance type (PLSD‐T) is a rare skeletal dysplasia characterized by platyspondyly, brachydactyly, and metaphyseal changes. Generally a perinatally lethal disease, a few long‐term survivors have been reported. Recently, mutations in the carboxy‐propeptide of type II collagen have been identified in two patients with PLSD‐T, indicating that PLSD‐T is a type 2 collagen‐associated disorder. We studied eight additional cases of PLSD‐T and found that all had mutations in the C‐propeptide domain of COL2A1. The mutational spectrum includes missense, stop codon and frameshift mutations. All non‐sense mutations were located in the last exon, where they would escape non‐sense‐mediated RNA‐decay. We conclude that PLSD‐T is caused by mutations in the C‐propeptide domain of COL2A1, which lead to biosynthesis of an altered collagen chain (as opposed to a null allele). Similar mutations have recently been found to be the cause of spondyloperipheral dysplasia, a non‐lethal dominant disorder whose clinical and radiographical features overlap those of the rare long‐term survivors with PLSD‐T. Thus, spondyloperipheral dysplasia and PLSD‐T constitute a novel subfamily within the type II collagenopathies, associated with specific mutations in the C‐propeptide domain and characterized by distinctive radiological features including metaphyseal changes and brachydactyly that set them apart from other type 2 collagenopathies associated with mutations in the triple‐helical domain of COL2A1. The specific phenotype of C‐propeptide mutations could result from a combination of diminished collagen fibril formation, toxic effects through the accumulation of unfolded collagen chains inside the chondrocytes, and alteration of a putative signaling function of the carboxy‐propeptide of type 2 collagen.

Mutations in MMP9 and MMP13 Determine the Mode of Inheritance and the Clinical Spectrum of Metaphyseal Anadysplasia

The matrix metalloproteinases MMP9 and MMP13 catalyze the degradation of extracellular matrix (ECM) components in the growth plate and at the same time cleave and release biologically active molecules stored in the ECM, such as VEGFA. In mice, ablation of Mmp9, Mmp13, or both Mmp9 and Mmp13 causes severe distortion of the metaphyseal growth plate. We report that mutations in either MMP9 or MMP13 are responsible for the human disease metaphyseal anadysplasia (MAD), a heterogeneous group of disorders for which a milder recessive variant and a more severe dominant variant are known. We found that recessive MAD is caused by homozygous loss of function of either MMP9 or MMP13, whereas dominant MAD is associated with missense mutations in the prodomain of MMP13 that determine autoactivation of MMP13 and intracellular degradation of both MMP13 and MMP9, resulting in a double enzymatic deficiency.

Spondyloperipheral dysplasia is caused by truncating mutations in the C-propeptide of COL2A1.

The term “spondyloperipheral dysplasia” (SPD) has been applied to the unusual combination of platyspondyly and brachydactyly as observed in a small number of individuals. The reported cases show wide clinical variability and the nosologic status and spectrum of this condition are still ill defined. Zabel et al. [1996: Am J Med Genet 63(1):123–128] reported an individual with short stature and SPD who was heterozygous for a frameshift mutation in the C‐propeptide domain of COL2A1. To explain the additional finding of brachydactyly that is not an usual feature of the type II collagenopathies, it was postulated that the nature of the mutation induced precocious calcification and premature fusion of metacarpal and phalangeal growth plates. The C‐propeptide of collagen II had previously been found to promote calcification (“chondrocalcin”). We have ascertained two further individuals with clinical and radiological findings of a type II collagenopathy in infancy who developed brachydactyly type E like changes of fingers and toes in childhood. In both individuals, heterozygosity for novel, distinct mutations in the C‐propeptide coding region of COL2A1 were found. Although all three mutations (the one previously reported and the two novel ones) predict premature termination, their location close to the 3′‐end of the mRNA probably protects them from nonsense‐mediated decay and allows for synthesis of mutant procollagen chains. However, loss of crucial cysteine residues or other sequences essential for trimerization prevents these chains from associating and participating in procollagen helix formation, and thus leads to accumulation in the ER‐consistent with EM findings. The mechanism leading to precocious fusion of phalangeal epiphyses remains to be explored. The consistency of clinical, radiographic, and molecular findings in these three unrelated individuals confirms SPD as a distinct nosologic entity. The diagnosis of SPD is suggested by the appearance of brachydactyly in a child who has clinical and radiographic features of a collagen II disorder.

Human fibroblast growth factor receptor 3 gene (FGFR3): genomic sequence and primer set information for gene analysis

Abstract We have determined the nucleotide sequence of the human fibroblast growth factor receptor 3 (FGFR3) gene, including 800 bp of the 5′-flanking region and compared the sequence with the previously published murine Fgfr3 gene. The organization of the gene is highly conserved between man and mouse. We used the intron sequences to design a set of primers that allow amplification of the 17 exons (2–18) that encode the complete open reading frame. Using these primers the FGFR3 gene can be amplified at the genomic level, which significantly facilitates mutational screening.

Du Pan syndrome phenotype caused by heterozygous pathogenic mutations in CDMP1 gene.

Du Pan syndrome is a rare acromesomelic dysplasia with characteristic clinical and radiographic findings. It is inherited as an autosomal recessive trait. Almost all the patients reported have been from Muslim countries. We report on a female and her child with Du Pan syndrome from a Caucasian, Polish family. Three new heterozygous mutations clustered on one allele of the CDMP1 gene were identified in the affected individuals resulting in the first familial case with dominant Du Pan syndrome. A possible synergistic effect of the cis‐acting mutations located in the active domain of the mature CDMP1 protein is likely to be responsible for the clinical expression of the disorder.