Clinical and Functional Characterization of a Patient Carrying a Compound Heterozygous Pericentrin Mutation and a Heterozygous IGF1 Receptor Mutation

Intrauterine and postnatal longitudinal growth is controlled by a strong genetic component that regulates a complex network of endocrine factors integrating them with cellular proliferation, differentiation and apoptotic processes in target tissues, particularly the growth centers of the long bones. Here we report on a patient born small for gestational age (SGA) with severe, proportionate postnatal growth retardation, discreet signs of skeletal dysplasia, microcephaly and moyamoya disease. Initial genetic evaluation revealed a novel heterozygous IGF1R p.Leu1361Arg mutation affecting a highly conserved residue with the insulin-like growth factor type 1 receptor suggestive for a disturbance within the somatotropic axis. However, because the mutation did not co-segregate with the phenotype and functional characterization did not reveal an obvious impairment of the ligand depending major IGF1R signaling capabilities a second-site mutation was assumed. Mutational screening of components of the somatotropic axis, constituents of the IGF signaling system and factors involved in cellular proliferation, which are described or suggested to provoke syndromic dwarfism phenotypes, was performed. Two compound heterozygous PCNT mutations (p.[Arg585X];[Glu1774X]) were identified leading to the specification of the diagnosis to MOPD II. These investigations underline the need for careful assessment of all available information to derive a firm diagnosis from a sequence aberration

Clinical data of the patient.

<p>A, Growth and weight charts of the patient. On the growth chart solid lines indicate 97th, 50th and 3rd percentiles; the shaded green area exhibits target height calculated from parent's height (blue triangle, father's height; red square, mother's height); red bar assigns period of rhGH therapy; grey squares mark the corrected age for preterm infants. B, Photograph of the patient at the age of 5.7 yrs. in comparison to a 5.8 yrs. old boy. C, Head circumference (HC) chart of the patient; 97th, 50th and 3rd percentiles are indicated as black solid lines, white circles mark the corrected age for preterm infants. D, Photograph of the patient's hypoplastic teeth.</p

IGF1 induced IGF1R phosphorylation and downstream signaling.

<p>A, Wild type and L1361R mutant IGF1R autophosphorylation in transiently transfected R⁻ cells after stimulation with 10 nM IGF1 for 0–30 minutes. Immunoblots were incubated with specific antibodies against phosphorylated IGF1R β-subunit (P-IGF1R), Akt (P-Akt) or Mapk/Erk (P-Mapk/Erk), stripped and subsequently incubated with specific antibodies against the IGF1R α-subunit (IGF1R), Akt (Akt), or Mapk/Erk (Mapk/Erk). IGF1R α-subunit levels were assessed as control of successful transfection. Densitometric units were normalized to total levels of IGF1R α-subunit and the fold increase was calculated (IGF1R-WT at 0 min was set 1). Results are shown as means ± SEM calculated from four independent experiments. B, Yeast two-hybrid analysis of the interaction of the IGF1R derivatives (IGF1R-C-WT, IGF1R-C-L1361R, IGF1R-C-KD) with adapter proteins (IRS1, 14-3-3ß, GIPC, PI3Kp85) by lift-off assay (left panel). Positive interactions led to blue staining (here black) of the colonies. POS, positive control p53 x large T-antigen; NEG, negative control Lamin x large T-antigen. The filter assays shown are representative for more than three independent experiments. Quantification of protein-protein interaction was measured using ONPG-assays and data are shown as mean ± SEM (right panel).</p

Sequence comparison of the IGF1R carboxyl terminus among different species.

*<p>) amino acid numbering according to human UniProtKB acc. P08069; position of the patient's mutation is marked in bold.</p