Lethal osteosclerotic skeletal dysplasia with intracellular inclusion bodies

In vivo cellular adaptation to ER stress: survival strategies with double-edged consequences

Disturbances to the balance of protein synthesis, folding and secretion in the endoplasmic reticulum (ER) induce stress and thereby the ER stress signaling (ERSS) response, which alleviates this stress. In this Commentary, we review the emerging idea that ER stress caused by abnormal physiological conditions and/or mutations in genes that encode client proteins of the ER is a key factor underlying different developmental processes and the pathology of diverse diseases, including diabetes, neurodegeneration and skeletal dysplasias. Recent studies in mouse models indicate that the effect of ERSS in vivo and the nature of the cellular strategies induced to ameliorate pathological ER stress are crucial factors in determining cell fate and clinical disease features. Importantly, ERSS can affect cellular proliferation and the differentiation program; cells that survive the stress can become 'reprogrammed' or dysfunctional. These cell-autonomous adaptation strategies can generate a spectrum of context-dependent cellular consequences, ranging from recovery to death. Secondary effects can include altered cell-extracellular-matrix interactions and non-cell-autonomous alteration of paracrine signaling, which contribute to the final phenotypic outcome. Recent reports showing that ER stress can be alleviated by chemical compounds suggest the potential for novel therapeutic approaches.

A new syndrome of congenital generalized osteosclerosis and bilateral polymicrogyria

We report a 29-week male fetus with healthy consanguineous parents. He showed a severe sclerosing bone disorder affecting all skeletal elements, resulting in insufficient modeling, generalized densification, and fragility of the skeleton. This skeletal dysplasia was associated with an abnormal craniofacial development (hypertelorism, severe microretrognathia, cleft palate, absent epiglottis, reduced number, and mineralization of teeth buds) and abnormal terminal phalanges. Neuropathologic examination showed bilateral fronto-parietal cerebral polymicrogyria. This syndrome appears to represent a new variant of congenital sclerotic bone disorder of unknown origin. Autosomal recessive inheritance is possible.

Dyssegmental dysplasia, Silverman-Handmaker type, is caused by functional null mutations of the perlecan gene

Perlecan is a large heparan sulfate (HS) proteoglycan present in all basement membranes and in some other tissues such as cartilage, and is implicated in cell growth and differentiation. Mice lacking the perlecan gene (Hspg2) have a severe chondrodysplasia with dyssegmental ossification of the spine and show radiographic, clinical and chondro-osseous morphology similar to a lethal autosomal recessive disorder in humans termed dyssegmental dysplasia, Silverman-Handmaker type (DDSH; MIM 224410). Here we report a homozygous, 89-bp duplication in exon 34 of HSPG2 in a pair of siblings with DDSH born to consanguineous parents, and heterozygous point mutations in the 5' donor site of intron 52 and in the middle of exon 73 in a third, unrelated patient, causing skipping of the entire exons 52 and 73 of the HSPG2 transcript, respectively. These mutations are predicted to cause a frameshift, resulting in a truncated protein core. The cartilage matrix from these patients stained poorly with antibody specific for perlecan, but there was staining of intracellular inclusion bodies. Biochemically, truncated perlecan was not secreted by the patient fibroblasts, but was degraded to smaller fragments within the cells. Thus, DDSH is caused by a functional null mutation of HSPG2. Our findings demonstrate the critical role of perlecan in cartilage development.