Lucy Shapiro, Sumana Chatterjee, Dina G Ramadan, Kate M Davies, Martin O Savage, Louise A Metherell, and Helen L Storr
GH insensitivity (GHI) is characterised by short stature, IGF-1 deficiency and normal/elevated serum GH. IGF-1 insensitivity results in pre- and post-natal growth failure with normal/high IGF-1 levels. The prevalence of genetic defects is unknown.
To identify the underlying genetic diagnoses in a paediatric cohort with GH or IGF-1 insensitivity using candidate gene (CGS) and whole-exome sequencing (WES) and assess factors associated with the discovery of a genetic defect.
We undertook a prospective study of 132 patients with short stature and suspected GH or IGF-1 insensitivity referred to our centre for genetic analysis. 107 (96 GHI, 88 probands; 11 IGF-1 insensitivity, 9 probands) underwent CGS. WES was performed in those with no defined genetic aetiology following CGS.
A genetic diagnosis was discovered 38/107 (36%) patients (32% probands) by CGS. WES revealed 11 patients with genetic variants in genes known to cause short stature. A further 2 patients had hypomethylation in the H19/IGF2 region or mUPD7 consistent with Silver–Russell Syndrome (total with genetic diagnosis 51/107, 48% or 41/97, 42% probands). WES also identified homozygous putative variants in FANCA and PHKB in 2 patients. Low height SDS and consanguinity were highly predictive for identifying a genetic defect.
Comprehensive genetic testing confirms the genetic heterogeneity of GH/IGF-1 insensitivity and successfully identified the genetic aetiology in a significant proportion of cases. WES is rapid and may isolate genetic variants that have been missed by traditional clinically driven genetic testing. This emphasises the benefits of specialist diagnostic centres.
Sumana Chatterjee, Lucy Shapiro, Stephen J Rose, Talat Mushtaq, Peter E Clayton, Svetlana B Ten, Amrit Bhangoo, Uma Kumbattae, Renuka Dias, Martin O Savage, Louise A Metherell, and Helen L Storr
Patients with homozygous intronic pseudoexon GH receptor (GHR) mutations (6Ψ) have growth hormone insensitivity (GHI) (growth failure, IGF1 deficiency and normal/elevated serum GH). We report 9 patients in addition to previously described 11 GHR 6Ψ patients and their responses to rhIGF1 therapy.
20 patients (12 males, 11 families, mean age 4.0 ± 2.2 years) were diagnosed genetically in our centre. Phenotypic data and responses to rhIGF1 treatment were provided by referring clinicians. Continuous parametric variables were compared using Student t-test or ANOVA.
10/20 (50%) had typical facial features of GHI, 19/20 (95%) from consanguineous families and 18/20 (90%) of Pakistani origin. At diagnosis, mean height SDS: −4.1 ± 0.95, IGF1 SDS: −2.8 ± 1.4; IGFBP3 SDS: −3.0 ± 2.1 and mean basal and peak GH levels: 11.9 µg/L and 32.9 µg/L, respectively. 1/12 who had IGF1 generation test, responded (IGF1: 132–255 ng/mL). 15/20 (75%; 11M) received rhIGF1 (mean dose: 114 µg/kg twice daily, mean duration: 5.3 ± 2.5 years). Mean baseline height velocity of 4.7 ± 1.1 cm/year increased to 7.4 ± 1.8 cm/year (P = 0.001) during year 1 of therapy. Year 3 mean height SDS (−3.2 ± 1.0) was higher than pre-treatment height SDS (−4.3 ± 0.8) (P = 0.03). Mean cumulative increase in height SDS after year 5 was 1.4 ± 0.9. Difference between target height (TH) SDS and adult or latest height SDS was less than that of TH SDS and pre-treatment height SDS (2.1 ± 1.2 vs 3.0 ± 0.8; P = 0.02).
In addition to phenotypic heterogeneity in the cohort, there was mismatch between clinical and biochemical features in individual patients with 6Ψ GHR mutations. rhIGF1 treatment improved height outcomes.
Emily Cottrell, Claudia P Cabrera, Miho Ishida, Sumana Chatterjee, James Greening, Neil Wright, Artur Bossowski, Leo Dunkel, Asma Deeb, Iman Al Basiri, Stephen J Rose, Avril Mason, Susan Bint, Joo Wook Ahn, Vivian Hwa, Louise A Metherell, Gudrun E Moore, and Helen L Storr
Copy number variation (CNV) has been associated with idiopathic short stature, small for gestational age and Silver-Russell syndrome (SRS). It has not been extensively investigated in growth hormone insensitivity (GHI; short stature, IGF-1 deficiency and normal/high GH) or previously in IGF-1 insensitivity (short stature, high/normal GH and IGF-1).
Design and methods
Array comparative genomic hybridisation was performed with ~60 000 probe oligonucleotide array in GHI (n = 53) and IGF-1 insensitivity (n = 10) subjects. Published literature, mouse models, DECIPHER CNV tracks, growth associated GWAS loci and pathway enrichment analyses were used to identify key biological pathways/novel candidate growth genes within the CNV regions.
Both cohorts were enriched for class 3–5 CNVs (7/53 (13%) GHI and 3/10 (30%) IGF-1 insensitivity patients). Interestingly, 6/10 (60%) CNV subjects had diagnostic/associated clinical features of SRS. 5/10 subjects (50%) had CNVs previously reported in suspected SRS: 1q21 (n = 2), 12q14 (n = 1) deletions and Xp22 (n = 1), Xq26 (n = 1) duplications. A novel 15q11 deletion, previously associated with growth failure but not SRS/GHI was identified. Bioinformatic analysis identified 45 novel candidate growth genes, 15 being associated with growth in GWAS. The WNT canonical pathway was enriched in the GHI cohort and CLOCK was identified as an upstream regulator in the IGF-1 insensitivity cohorts.
Our cohort was enriched for low frequency CNVs. Our study emphasises the importance of CNV testing in GHI and IGF-1 insensitivity patients, particularly GHI subjects with SRS features. Functional experimental evidence is now required to validate the novel candidate growth genes, interactions and biological pathways identified.