A new p.(Ile66Serfs*93) IGF2 variant is associated with pre- and postnatal growth retardation

Abstract

Objective: The IGF/IGF1R axis is involved in the regulation of human growth. Both IGF1 and IGF2 can bind to the IGF1R in order to promote growth via the downstream PI3K/AKT pathway. Pathogenic mutations in IGF1 and IGF1R determine intrauterine growth restriction and affect postnatal body growth. However, to date, there are only few reports of pathogenic IGF2 mutations causing severe prenatal, as well as postnatal growth retardation. Results: Here we describe a de novo c.195delC IGF2 variant (NM_000612, p.(Ile66Serfs*93)) in a 4-year-old patient with severe pre-and postnatal growth retardation in combination with dystrophy, facial dimorphism, finger deformities, as well as a patent ductus. Cloning and sequencing of a long-range PCR product harboring the deletion and a SNP informative site chr11:2153634 (rs680, NC_000011.9:g.2153634T>C) demonstrated that the variant resided on the paternal allele. This finding is consistent with the known maternal imprinting of IGF2. 3D protein structure prediction and overexpression studies demonstrated that the p.(Ile66Serfs*93) IGF2 gene variation resulted in an altered protein structure that impaired ligand/receptor binding and thus prevents IGF1R activation. Conclusion: The severity of the phenotype in combination with the dominant mode of transmission provides further evidence for the involvement of IGF2 in growth disorders. Figure 3Illustration of potential conformational changes in p.I66S protein structure. (A) Schematic diagram of IGF2 maturation. IGF2 encodes an inactive 180-aa precursor protein which is post-translationally cleaved into a 67-aa bioactive protein. First, the terminal signal peptide is proteolytically removed creating a 156-aa sequence. In the next step, the trailer sequence is proteolytically cleaved at two separated sites (TQRLRR 104 and PAKSER 68 ) generating the bioactive protein. (B) Illustration of p.I66S protein structure. Sequence analyses of the cleavage sites indicated a changed aa sequence at basic residues in the mutant: TQRLRR→PSACAG and PAKSER→PPSPRG. (C) Comparison of the WT (IGF2-WT, blue) and mutant (IGF2-I66S, red) protein structure.3D protein structure was predicted based on the crystal structure of IGF2-WT (pdb: 1IGL) using the iTASSER server and superpositioned with the WT structure. The mostly unstructured C-terminal extension due to the lack of posttranslational processing is illustrated. (D) Upper panel: Schematic presentation of IGF2 plasmids. The position of the c.195delC mutation is marked in red. Lower panel: Cell lysates and supernatants from transfected cells after immunoblotting with the indicated antibodies. (E) Whole-cell lysates from IGF1 stimulated (30 min) cells transfected with an IGF1R plasmid were subjected to immunoblotting using antibodies as indicated. (F) Whole-cell lysates were prepared from IGF1R transfected cells after stimulation (30 min) with IGF2-WT supernatants and immunoblotted for pIGF1R, total IGF1R and β-actin as loading control. Representative blot out of three independent experiments is shown.Figure 4...

Novel mutation points to a hot spot in CDKN1C causing Silver–Russell syndrome

“…Body asymmetry, a frequent characteristic in SRS caused by mosaic IC1 hypomethylation, was absent in the index patient and his affected mother. This is in agreement with the previous clinical findings in patients with the p.Arg279Leu variant [4,5], the sporadic case from Japan [6] and other patients with SRS and genomic mutations of IGF2 which were not mosaic [20][21][22][23][24]. In agreement with a previous report [5], IGF-1 serum levels were normal in the index patient and his mother.…”

“…Since the first report of a genomic IGF2 mutation in familial SRS by Begemann et al [ 12 ], eleven additional IGF2 mutations in only sporadic cases were reported [ 13 , 20 – 24 ]. This number is not high, but higher than the three families and one sporadic case reported with genomic CDKN1C mutations and SRS ([ 4 – 6 ], this study).…”

Placental genotype affects early postpartum maternal behaviour

“…Correct dosage of placental imprinted genes is critical to both functions [4,10,15,17]. However, while placental misexpression of individual imprinted genes affects conceptus growth in predictable and repeatable directions [60,61], effects on maternal behaviour and physiology are considerably less studied and can differ across studies [25,27]. To our knowledge, the effects of altered placental expression on wild-type female mice have been tested for only three imprinted genes: Peg3 , Grb10 and Phlda2 [25,26,28,30].…”

Update on new GH-IGF axis genetic defects

“…Through exome analysis, the authors identified an IGF2 nonsense mutation in all patients, inherited from their healthy fathers (OMIM 616489) (51). After this first report, other five studies identified variants in IGF2 gene on the paternal allele causing SRS-like (52)(53)(54)(55)(56). Up to now, one missense and six loss-of-function variants (3 frameshift, 2 nonsense and 1 splice-site) in the IGF2 gene were reported.…”

“…Five probands presented cardiac abnormalities, including patent ductus arteriosus and atrial or ventricular septal defects. Male genital abnormalities, as hypospadia, penoscrotal transposition, cryptorchidism and ambiguous genitalia were also reported (51)(52)(53)56).…”