Endocrine Abstracts

Introduction: 3-M syndrome is an autosomal recessive disorder characterised by pre- and postnatal growth restriction, characteristic facial dysmorphism, normal intelligence and radiological features (slender long bones and tall vertebral bodies). It is known to be caused by mutations in the genes encoding Cullin 7 (a component of the ubiquitination system) and Obscurin like-1 (a cytoskeletal protein). The mechanisms through which mutations in these genes impair growth are unclear.

Aims: The aim of this study was to identify novel pathways involved in the growth impairment in 3-M syndrome.

Methods: RNA was extracted from fibroblast cell lines derived from four 3-M syndrome patients and 3 control subjects, hybridised to Affymetrix HU 133 plus 2.0 arrays with quantitative real time PCR used to confirm changes found on microarray. IGF2 protein levels in serum and conditioned cell culture medium were measured by ELISA.

Results: 1926 probesets differentially regulated between control and 3-M syndrome fibroblasts (defined as fold difference>2 and expression level>50 in one or more cell lines) were identified. 779 of these probesets were upregulated and 1147 downregulated. Of the top 10 downregulated probesets 3 represented IGF2 while H19 was identified as the 25 and 65th most upregulated probesets. qRT-PCR confirmed upregulation of H19 (P<0.001) and downregualtion of IGF2 (P<0.001).

Levels of IGF-2 secreted into conditioned cell culture medium were higher for control fibroblasts than for 3-M fibroblasts (10.2±8 vs 2.6±4.7 ng/ml, P<0.01). Serum IGF-2 levels did not appear reduced in 3-M syndrome (n=6 1390±212 ng/ml).

Conclusions: 3-M syndrome is associated with a gene expression profile of reduced IGF2 expression and increased H19 expression similar to that found in Silver Russell syndrome. Loss of autocrine IGF-2 in the growth plate may result in the short stature seen in children with 3-M syndrome.