Interstitial lung disease in an adolescent child associated with a novel STAT5B mutation-a case report

STAT5B protein is an important component of signalling pathway for growth hormone and IL-2 mediated responses. Mutation in STAT5B gene has been reported to be associated with growth hormone insensitivity, immunodeficiency and autoimmunity. Chronic pulmonary involvement is also one component of the disorder. We describe a case an adolescent girl who suffered with poor growth and loose stools since 1 year of age and was subsequently diagnosed with celiac disease and hypothyroidism. She developed features of interstitial lung disease (ILD) which were progressively worsening. Common causes of ILD were ruled out on investigations. She underwent whole exome sequencing and found to be positive for a novel mutation in STAT5B gene on exon 16. On further evaluation, she had growth hormone insensitivity and CD8 cell deficiency. This case highlights that in a child with chronic pulmonary involvement with features suggestive of growth hormone insensitivity, immunodeficiency and autoimmunity, evaluation for STAT5B mutation should be thought of.

Growth Hormone Receptor (Ghr) 6ω Pseudoexon Activation: A Novel Cause Of Severe Growth Hormone Insensitivity (Ghi)

Context Severe forms of Growth Hormone Insensitivity (GHI) are characterized by extreme short stature, dysmorphism and metabolic anomalies. Objective Identification of the genetic cause of growth failure in 3 ‘classical’ GHI subjects. Design A novel intronic GHR variant was identified, and in vitro splicing assays confirmed aberrant splicing. A 6Ω pseudoexon GHR vector and patient fibroblast analysis assessed the consequences of the novel pseudoexon inclusion and the impact on GHR function. Results We identified a novel homozygous intronic GHR variant (g.5:42700940T>G, c.618 + 836T> G), 44bp downstream of the previously recognized intronic 6Ψ GHR pseudoexon mutation in the index patient. Two siblings also harbored the novel intronic 6Ω pseudoexon GHR variant in compound heterozygosity with the known GHR c.181C>T (R43X) mutation. In vitro splicing analysis confirmed inclusion of a 151bp mutant 6Ω pseudoexon not identified in wild-type constructs. Inclusion of the 6Ω pseudoexon causes a frameshift resulting in a non-functional truncated GHR lacking the transmembrane and intracellular domains. The truncated 6Ω pseudoexon protein demonstrated extracellular accumulation and diminished activation of STAT5B signaling following growth hormone stimulation. Conclusion Novel GHR 6Ω pseudoexon inclusion results in loss of GHR function consistent with a severe GHI phenotype. This represents a novel mechanism of Laron syndrome and is the first deep intronic variant identified causing severe postnatal growth failure. The 2 kindreds originate from the same town in Campania, Southern Italy, implying common ancestry. Our findings highlight the importance of studying variation in deep intronic regions as a cause of monogenic disorders.

Genetic characterization of short stature patients with overlapping features of growth hormone insensitivity syndromes

Context and objective Growth hormone insensitivity (GHI) in children is characterized by short stature, functional IGF-I deficiency and normal or elevated serum GH concentrations. The clinical and genetic etiology of GHI is expanding. We undertook genetic characterization of short stature patients referred with suspected GHI and features which overlapped with known GH-IGF-I axis defects. Design and methods Between 2008 and 2020, our center received 149 GHI referrals for genetic testing. Genetic analysis utilized a combination of candidate gene sequencing (CGS), whole exome sequencing (WES), array comparative genomic hybridization (aCGH) and a targeted whole genome short stature gene panel. Results Genetic diagnoses were identified in 80/149 subjects (54%) with 45/80 (56%) having known GH-IGF-I axis defects (GHR n=40, IGFALS n=4, IGFIR n=1). The remaining 35/80 (44%) had diagnoses of 3M syndrome (n=10) (OBSL1 n=7, CUL7 n=2 and CCDC8 n=1), Noonan syndrome (n=4) (PTPN11 n=2, SOS1 n=1 and SOS2 n=1), Silver-Russell syndrome (n=2) (Loss of methylation on chromosome 11p15 and uniparental disomy for chromosome 7), Class 3-5 copy number variations (n=10) and disorders not previously associated with GHI (n=9) (Barth syndrome, Autoimmune lymphoproliferative syndrome, Microcephalic osteodysplastic primordial dwarfism Type II, Achondroplasia, Glycogen storage disease Type IXb, Lysinuric protein intolerance, Multiminicore Disease, MACS syndrome and Bloom syndrome). Conclusion We report the wide range of diagnoses in 149 patients referred with suspected GHI, which emphasizes the need to recognize GHI as a spectrum of clinical entities in undiagnosed short stature patients. Detailed clinical and genetic assessment may identify a diagnosis and inform clinical management.

Rare CNVs provide novel insights into the molecular basis of GH and IGF-1 insensitivity

Objective 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. Results 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. Conclusions 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.

GHR gene transcript heterogeneity may explain phenotypic variability in GHR pseudoexon (6Ψ) patients

Objectives The homozygous GH receptor (GHR) pseudoexon (6Ψ) mutation leads to growth hormone insensitivity (GHI) with clinical and biochemical heterogeneity. We investigated whether transcript heterogeneity (6Ψ-GHR to WT-GHR transcript ratio) and/or concurrent defects in other short stature (SS) genes contribute to this. Methods 6Ψ-GHR and WT-GHR mRNA transcripts of four 6Ψ patients (height SDS −4.2 to −3.1) and one control fibroblast were investigated by RT-PCR. Transcripts were quantified by qRT-PCR and delta delta CT analysis and compared using ANOVA with Bonferroni correction. In eleven 6Ψ patients, 40 genes known to cause GHI/SS were analysed by targeted next generation sequencing. Results RT-PCR confirmed 6Ψ-GHR transcript in the 6Ψ patients but not in the control. 6Ψ-GHR transcript levels were comparable in patients 1 and 3 but significantly different among all other patients. The mean 6Ψ:WT transcript ratios ranged from 29–71:1 for patients 1–4 and correlated negatively with height SDS (R = −0.85; P < 0.001). Eight deleterious variants in six genes were detected, but the number of gene hits did not correlate with the degree of SS in individual 6Ψ patients. Conclusion Variable amounts of 6Ψ- and WT-GHR transcripts were identified in 6Ψ patients but no 6Ψ transcript was present in the control. Higher 6Ψ:WT-GHR transcript ratio correlated with SS severity and may explain the phenotypic variability. Analysis of known SS genes suggested that phenotypic variation is independent of the genetic background. This is the first report of transcript heterogeneity producing a spectrum of clinical phenotypes in different individuals harbouring an identical homozygous genetic mutation.