Effectiveness of growth hormone therapy in children with Noonan syndrome

Clinical and genetic evaluation of children with short stature of unknown origin

BACKGROUND

Short stature is a common human trait. More severe and/or associated short stature is usually part of the presentation of a syndrome and may be a monogenic disease. The present study aimed to identify the genetic etiology of children with short stature of unknown origin.

METHODS

A total of 232 children with short stature of unknown origin from March 2013 to May 2020 were enrolled in this study. Whole exome sequencing (WES) was performed for the enrolled patients to determine the underlying genetic etiology.

RESULTS

We identified pathogenic or likely pathogenic genetic variants in 18 (7.8%) patients. All of these variants were located in genes known to be associated with growth disorders. Five of the genes are associated with paracrine signaling or cartilage extracellular matrix in the growth plate, including NPR2 (N = 1), ACAN (N = 1), CASR (N = 1), COMP (N = 1) and FBN1 (N = 1). Two of the genes are involved in the RAS/MAPK pathway, namely, PTPN11 (N = 6) and NF1 (N = 1). Two genes are associated with the abnormal growth hormone-insulin-like growth factor 1 (GH-IGF1) axis, including GH1 (N = 1) and IGF1R (N = 1). Two mutations are located in PROKR2, which is associated with gonadotropin-releasing hormone deficiency. Mutations were found in the remaining two patients in genes with miscellaneous mechanisms: ANKRD11 (N = 1) and ARID1A (N = 1).

CONCLUSIONS

The present study identified pathogenic or likely pathogenic genetic variants in eighteen of the 232 patients (7.8%) with short stature of unknown origin. Our findings suggest that in the absence of prominent malformation, genetic defects in hormones, paracrine factors, and matrix molecules may be the causal factors for this group of patients. Early genetic testing is necessary for accurate diagnosis and precision treatment.

Efficacy and safety of growth hormone therapy in children with Noonan syndrome

Patients with Noonan syndrome typically have a target height <2 standard deviations compared to the general population, and half of the affected adults remain permanently below the 3rd centile for height, though their short stature might result from a multifactorial etiology, not-yet fully understood. The secretion of growth hormone (GH) following the classic GH stimulation tests is often normal, with baseline insulin-like growth factor-1 (IGF-1) levels at the lower normal limits, but patients with Noonan syndrome have also a possible moderate response to GH therapy, leading to a final increased height and substantial improvement in growth rate. Aim of this review was to evaluate both safety and efficacy of GH therapy in children and adolescents with Noonan syndrome, also evaluating as a secondary aim the possible correlations between the underlying genetic mutations and GH responses.

Inside the Noonan "universe": Literature review on growth, GH/IGF axis and rhGH treatment: Facts and concerns

Noonan syndrome (NS) is a disorder characterized by a typical facial gestalt, congenital heart defects, variable cognitive deficits, skeletal defects, and short stature. NS is caused by germline pathogenic variants in genes coding proteins with a role in the RAS/mitogen-activated protein kinase signaling pathway, and it is typically associated with substantial genetic and clinical complexity and variability. Short stature is a cardinal feature in NS, with evidence indicating that growth hormone (GH) deficiency, partial GH insensitivity, and altered response to insulin-like growth factor I (IGF-1) are contributing events for growth failure in these patients. Decreased IGF-I, together with low/normal responses to GH pharmacological provocation tests, indicating a variable presence of GH deficiency/resistance, in particular in subjects with pathogenic PTPN11 variants, are frequently reported. Nonetheless, short- and long-term studies have demonstrated a consistent and significant increase in height velocity (HV) in NS children and adolescents treated with recombinant human GH (rhGH). While the overall experience with rhGH treatment in NS patients with short stature is reassuring, it is difficult to systematically compare published data due to heterogeneous protocols, potential enrolment bias, the small size of cohorts in many studies, different cohort selection criteria and varying durations of therapy. Furthermore, in most studies, the genetic information is lacking. NS is associated with a higher risk of benign and malignant proliferative disorders and hypertrophic cardiomyopathy, and rhGH treatment may further increase risk in these patients, especially as dosages vary widely. Herein we provide an updated review of aspects related to growth, altered function of the GH/IGF axis and cell response to GH/IGF stimulation, rhGH treatment and its possible adverse events. Given the clinical variability and genetic heterogeneity of NS, treatment with rhGH should be personalized and a conservative approach with judicious surveillance is recommended. Depending on the genotype, an individualized follow-up and close monitoring during rhGH treatments, also focusing on screening for neoplasms, should be considered.

Growth in Children With Noonan Syndrome and Effects of Growth Hormone Treatment on Adult Height

OBJECTIVES

Growth impairment is a common manifestation in Noonan syndrome (NS). Recombinant human GH (rhGH) treatment has been shown to increase growth and adult height (AH) in a few studies. We aimed to evaluate the growth trajectory towards the AH, and the effects of rhGH treatment in a large cohort of NS children.

METHODS

Retrospective, multicenter, cohort study including subjects with genetic diagnosis of NS. A total of 228 NS patients, 154 with PTPN11 mutations, 94 who reached AH, were recruited. Auxological data were collected at 2, 5, and 10 years, at pubertal onset, at AH. Sixty-eight NS subjects affected with GH deficiency (GHD) were treated with rhGH at a mean dose of 0.24 mg/kg per week until AH achievement.

RESULTS

ANOVA analysis showed a significant difference between birth length and height standard deviation scores (HSDS) at the different key ages (p<0.001), while no significant differences were found between HSDS measurements at 2, 5, and 10 years, at pubertal onset, and at AH. HSDS increased from -3.10 ± 0.84 to -2.31 ± 0.99 during rhGH treatment, with a total height gain of 0.79 ± 0.74, and no significant difference between untreated and treated NS at AH.

CONCLUSIONS

rhGH treatment at the standard dose used for children with GH idiopathic deficiency is effective in improving growth and AH in NS with GHD. Further studies are needed to assess genotype-specific response to rhGH treatment in the different pathogenic variants of PTPN11 gene and in the less common genotypes.