IHH Gene Mutations Causing Short Stature With Nonspecific Skeletal Abnormalities and Response to Growth Hormone Therapy

Approach to the Peripubertal Patient With Short Stature

CONTEXT

The assessment and treatment of children with growth retardation is increasingly complex, and due to availability of targeted genetic sequencing, an ever-expanding number of conditions impeding growth are being identified. Among endocrine-related etiologies of short stature amenable to hormonal treatment, defects in the growth hormone (GH)-insulin-like growth factor I axis remain pre-eminent, with a multiplicity of disorders causing decreased secretion or insensitivity to GH action. Sex steroids in puberty increase epiphyseal senescence and eventual growth plate closure. This is mediated mostly via estrogen receptor (ER)α in males and females, effects that can greatly limit time available for growth.

EVIDENCE ACQUISITION

Extensive literature review through PubMed and other search engines.

EVIDENCE SYNTHESIS

Therapeutic strategies to be considered in peripubertal and pubertal children with disordered growth are here discussed, including daily and weekly GH, low-dose sex steroids, gonadotropin hormone releasing hormone (GnRH) analogues in combination with GH, aromatase inhibitors (AIs) alone and in combination with GH in boys. When used for at least 2 to 3 years, GnRH analogues combined with GH can result in meaningful increases in height. AIs used with GH permit puberty to progress in boys without hindrance, selectively decreasing estrogen, and resulting in taller height. With more than 20 years of cumulative experience in clinical use of these medications, we discuss the safety profile of these treatments.

CONCLUSION

The approach of growth retardation in the peripubertal and pubertal years must consider the sex steroid milieu and the tempo of bone acceleration. Treatment of affected children in this period must be individualized.

Exome Sequencing Identifies Multiple Genetic Diagnoses in Children with Syndromic Growth Disorders

OBJECTIVE

To evaluate the presence of multiple genetic diagnoses in syndromic growth disorders.

STUDY DESIGN

We carried out a cross-sectional study to evaluate 115 patients with syndromic tall (n = 24) or short stature (n = 91) of unknown cause from a tertiary referral center for growth disorders. Exome sequencing was performed to assess germline single nucleotide, InDel, and copy number variants. All variants were classified according to ACMG/AMP guidelines. The main outcome measured was the frequency of multiple genetic diagnoses in a cohort of children with syndromic growth disorders.

RESULTS

The total diagnostic yield of the cohort was 54.8% (63/115). Six patients had multiple genetic diagnoses (tall stature group = 2; short stature group = 4). The proportion of multiple diagnoses within total cases was 5.2% (6/115), and within solved cases was 9.5% (6/63). No characteristics were significantly more frequent when compared with patients with single or multiple genetic findings. Among patients with multiple diagnoses, 3 had syndromes with overlapping clinical features, and the others had syndromes with distinct phenotypes.

CONCLUSION

Recognition of multiple genetic diagnoses as a possibility in complex cases of syndromic growth disorders opens a new perspective on treatment and genetic counseling for affected patients, defying the medical common sense of trying to fit all findings into one diagnosis.

Exploring the Genetic Causes for Postnatal Growth Failure in Children Born Non-Small for Gestational Age

The most common causes of short stature (SS) in children are familial short stature (FSS) and idiopathic short stature (ISS). Recently, growth plate dysfunction has been recognized as the genetic cause of FSS or ISS. The aim of this study was to investigate monogenic growth failure in patients with ISS and FSS. Targeted exome sequencing was performed in patients categorized as ISS or FSS and the subsequent response to growth hormone (GH) therapy was analyzed. We found 17 genetic causes involving 12 genes (NPR2, IHH, BBS1, COL1A1, COL2A1, TRPS1, MASP1, SPRED1, PTPTN11, ADNP, NADSYN1, and CERT1) and 2 copy number variants. A genetic cause was found in 45.5% and 35.7% of patients with FSS and ISS, respectively. The genetic yield in patients with syndromic and non-syndromic SS was 90% and 23.1%, respectively. In the 11 genetically confirmed patients, a gain in height from -2.6 to -1.3 standard deviations after 2 years of GH treatment was found. The overall diagnostic yield in this study was 41.7%. We identified several genetic causes involving paracrine signaling, the extracellular matrix, and basic intracellular processes. Identification of the causative gene may provide prognostic evidence for the use of GH therapy in non-SGA children.

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.

Clinical and Genetic Characterization of Familial Central Precocious Puberty

CONTEXT

Central precocious puberty (CPP) can have a familial form in approximately one-quarter of the children. The recognition of this inherited condition increased after the identification of autosomal dominant CPP with paternal transmission caused by mutations in the MKRN3 and DLK1 genes.

OBJECTIVE

We aimed to characterize the inheritance and estimate the prevalence of familial CPP in a large multiethnic cohort; to compare clinical and hormonal features, as well as treatment response to GnRH analogs (GnRHa), in children with distinct modes of transmission; and to investigate the genetic basis of familial CPP.

METHODS

We retrospectively studied 586 children with a diagnosis of CPP. Patients with familial CPP (n = 276) were selected for clinical and genetic analysis. Data from previous studies were grouped, encompassing sequencing of MKRN3 and DLK1 genes in 204 patients. Large-scale parallel sequencing was performed in 48 individuals from 34 families.

RESULTS

The prevalence of familial CPP was estimated at 22%, with a similar frequency of maternal and paternal transmission. Pedigree analyses of families with maternal transmission suggested an autosomal dominant inheritance. Clinical and hormonal features, as well as treatment response to GnRHa, were similar among patients with different forms of transmission of familial CPP. MKRN3 loss-of-function mutations were the most prevalent cause of familial CPP, followed by DLK1 loss-of-function mutations, affecting, respectively, 22% and 4% of the studied families; both affected exclusively families with paternal transmission. Rare variants of uncertain significance were identified in CPP families with maternal transmission.

CONCLUSION

We demonstrated a similar prevalence of familial CPP with maternal and paternal transmission. MKRN3 and DLK1 loss-of-function mutations were the major causes of familial CPP with paternal transmission.

International Consensus Guideline on Small for Gestational Age (SGA): Etiology and Management from Infancy to Early Adulthood

This International Consensus Guideline was developed by experts in the field of SGA of 10 pediatric endocrine societies worldwide. A consensus meeting was held and 1300 articles formed the basis for discussions. All experts voted about the strengths of the recommendations. The guideline gives new and clinically relevant insights into the etiology of short stature after SGA birth, including novel knowledge about (epi)genetic causes. Besides, it presents long-term consequences of SGA birth and new treatment options, including treatment with gonadotropin-releasing hormone agonist (GnRHa) in addition to growth hormone (GH) treatment, and the metabolic and cardiovascular health of young adults born SGA after cessation of childhood-GH-treatment in comparison with appropriate control groups. To diagnose SGA, accurate anthropometry and use of national growth charts are recommended. Follow-up in early life is warranted and neurodevelopment evaluation in those at risk. Excessive postnatal weight gain should be avoided, as this is associated with an unfavorable cardio-metabolic health profile in adulthood. Children born SGA with persistent short stature < -2.5 SDS at age 2 years or < -2 SDS at age of 3-4 years, should be referred for diagnostic work-up. In case of dysmorphic features, major malformations, microcephaly, developmental delay, intellectual disability and/or signs of skeletal dysplasia, genetic testing should be considered. Treatment with 0.033-0.067 mg GH/kg/day is recommended in case of persistent short stature at age of 3-4 years. Adding GnRHa treatment could be considered when short adult height is expected at pubertal onset. All young adults born SGA require counseling to adopt a healthy lifestyle.

Idiopathic Short Stature: What to Expect from Genomic Investigations

Short stature is a common concern for physicians caring for children. In traditional investigations, about 70% of children are healthy, without producing clinical and laboratory findings that justify their growth disorder, being classified as having constitutional short stature or idiopathic short stature (ISS). In such scenarios, the genetic approach has emerged as a great potential method to understand ISS. Over the last 30 years, several genes have been identified as being responsible for isolated short stature, with almost all of them being inherited in an autosomal-dominant pattern. Most of these defects are in genes related to the growth plate, followed by genes related to the growth hormone (GH)–insulin-like growth factor 1 (IGF1) axis and RAS-MAPK pathway. These patients usually do not have a specific phenotype, which hinders the use of a candidate gene approach. Through multigene sequencing analyses, it has been possible to provide an answer for short stature in 10–30% of these cases, with great impacts on treatment and follow-up, allowing the application of the concept of precision medicine in patients with ISS. This review highlights the historic aspects and provides an update on the monogenic causes of idiopathic short stature and suggests what to expect from genomic investigations in this field.

SHOX Deletion and Idiopathic Short Stature: What Does the Clinician Need to Know? Case Series Report

Children diagnosticated with idiopathic short stature (ISS) are probably, in most cases, underdiagnosticated. The genetic causes of ISS may be mutations of genes involved in local regulation of the growth plate or genes involved in the GH-IGF1 axis physiology. We present a kindred of five children evaluated for short stature or low normal stature, initially diagnosticated as idiopathic short stature, familial short stature, or being small for gestational age. Clinical signs suggestive of SHOX deletion screening in a child with short stature are low arm span/height ratio, increased sitting height/height ratio, BMI > 50% percentile, Madelung deformity, cubitus valgus, bowing and shortening of the forearm, dislocation of the ulna (at the elbow), and the appearance of muscular hypertrophy. Radiological characteristics suggestive of SHOX deficiency are triangularisation of the distal radial epiphysis, an enlarged diaphysis of the radius plus bowing of the radius, the convexity of the distal radial metaphysis, short fourth and fifth metacarpals, pyramidalization of the carpal row. Treatment with rGH is approved for children with SHOX gene deficiency and short stature. This kindred is an example that familial short stature, idiopathic short stature, and short stature due to a small gestational age are not final diagnoses. Complex investigations are necessary to identify the precise cause, leading to optimal clinical management. Treatment with rGH is an option for some of them; for others, it has no therapeutic response and, in some cases, is even harmful.

Diagnostic yield of a multigene sequencing approach in children classified as idiopathic short stature

Objective

Most children with short stature remain without an etiologic diagnosis after extensive clinical and laboratory evaluation and are classified as idiopathic short stature (ISS). This study aimed to determine the diagnostic yield of a multigene analysis in children classified as ISS.

Design and methods

We selected 102 children with ISS and performed the genetic analysis as part of the initial investigation. We developed customized targeted panel sequencing, including all genes already implicated in the isolated short-stature phenotype. Rare and deleterious single nucleotide or copy number variants were assessed by bioinformatic tools.

Results

We identified 20 heterozygous pathogenic (P) or likely pathogenic (LP) genetic variants in 17 of 102 patients (diagnostic yield = 16.7%). Three patients had more than one P/LP genetic alteration. Most of the findings were in genes associated with the growth plate differentiation: IHH (n = 4), SHOX (n = 3), FGFR3 (n = 2), NPR2 (n = 2), ACAN (n = 2), and COL2A1 (n = 1) or involved in the RAS/MAPK pathway: NF1 (n = 2), PTPN11 (n = 1), CBL (n = 1), and BRAF (n = 1). None of these patients had clinical findings to guide a candidate gene approach. The diagnostic yield was higher among children with severe short stature (35% vs 12.2% for height SDS ≤ or > -3; P = 0.034). The genetic diagnosis had an impact on clinical management for four children.

Conclusion

A multigene sequencing approach can determine the genetic etiology of short stature in up to one in six children with ISS, removing the term idiopathic from their clinical classification.

Exogenous growth hormone functionally alleviates glucocorticoid-induced longitudinal bone growth retardation in male rats by activating the Ihh/PTHrP signaling pathway

Glucocorticoid (GC)-induced longitudinal bone growth retardation is a common and severe adverse effect in pediatric patients receiving GC immunosuppressive therapy. Molecular mechanisms underlying GC-induced growth inhibition are unclear. GC withdrawal following short-term high-dose use is common, including in the immediate post-transplant period. However, whether skeleton growth recovery is sufficient or whether growth-promoting therapy is required following GC withdrawal is unknown. The aim of this study was to investigate the effect of exogenous growth hormone (GH) on growth plate impairment in GC-induced longitudinal bone growth retardation. Here, apoptotic chondrocytes in the hypertrophic layer of growth plates increased whereas Indian Hedgehog (Ihh) and Parathyroid Hormone Related Peptide (PTHrP) protein levels in the growth plate decreased following GC exposure. The hypertrophic zone of the growth plate expanded following GC withdrawal. Subcutaneously injected GH penetrated the growth plate and modified its organization in rats following GC withdrawal. Ihh and PTHrP expression in GC-induced apoptotic chondrocytes decreased in vitro. GH promoted chondrocyte proliferation by activating Ihh/PTHrP signaling. Downregulating Ihh using specific siRNAs increased chondrocyte apoptosis and inhibited PTHrP, Sox9, and type II collagen (Col2a1) protein expression. GH inhibited apoptosis of Ihh-deficient growth plate chondrocytes by upregulating PTHrP, Sox9, and Col2a1 expression. Thus, reversal of the effect of GC on growth plate impairment following its withdrawal is insufficient, and exogenous GH provides growth plate chondral protection and improved longitudinal growth following GC withdrawal by acting on the Ihh/PTHrP pathway.

The evaluation of ovarian function in normosmic idiopathic hypogonadotropic hypogonadism with a fibroblast growth factor receptor 1 mutation: a case report

Normosmic idiopathic hypogonadotropic hypogonadism (nIHH) is a rare disorder with pubertal delay, normal sense of smell. nIHH with a fibroblast growth factor receptor 1 mutation is much more common in adult males but is rarely reported in females. In addition, the assessment and monitoring of ovarian function in nIHH females has often been ignored. We report a 24-year-old nIHH female with the complaint of primary amenorrhea and delayed secondary sexual traits development. Whole-Exome Sequencing analysis revealed a novel mutation in the third exon of fibroblast growth factor receptor 1 gene (c.289 G > A), which resulted in the replacement of glycine acid with serine. Then the patient was recommended to start with the hormone therapy (HT). After several months of estrogen combined with progesterone replacement, the patient had regular menstruation. The breast development and genital development gradually became Tanner stage 5. Anti-Müllerian hormones (AMHs) were also evaluated and the serum AMH level keeps fluctuating within the normal reference range. We highlight the great variability of fibroblast growth factor receptor 1 mutation phenotypes and the evaluation of ovarian reserve in nIHH, and the hormone replacement therapy is necessary to improve secondary sexual development for patients with nIHH.

Novel variant in HHAT as a cause of different sex development with partial gonadal dysgenesis associated with microcephaly, eye defects, and distal phalangeal hypoplasia of both thumbs: Case report

The palmitoylation of the Hedgehog (Hh) family of morphogens, named sonic hedgehog (SHH), desert hedgehog (DHH), and Indian hedgehog (IHH), is crucial for effective short- and long-range signaling. The hedgehog acyltransferase (HHAT) attaches the palmitate molecule to the Hh; therefore, variants in HHAT cause a broad spectrum of phenotypes. A missense HHAT novel variant c.1001T>A/p.(Met334Lys) was described in a patient first referred for a 46,XY different sexual development with partial gonadal dysgenesis but with microcephaly, eye defects, and distal phalangeal hypoplasia of both thumbs. The in silico analysis of the variant predicted an affectation of the nearest splicing site. Thus, in vitro minigene studies were carried out, which demonstrated that the variant does not affect the splicing. Subsequent protein in silico studies supported the pathogenicity of the variant, and, in conclusion, this was considered the cause of the patient's phenotype.

Brachydactyly Type A3 Is More Commonly Seen in Children With Short Stature But Does Not Affect Their Height Improvement by Growth Hormone Therapy

INTRODUCTION

To analyze the prevalence of brachydactyly type A3 (BDA3) in children with short stature and the effect on growth hormone (GH) therapy.

METHODS

We analyzed the medical records of pediatric patients from July 2009 to July 2021. We included children with short stature defined as their height standard deviation score (HtSDS) < -2 and normal short height as their HtSDS between -2 and -1. We calculated the prevalence of BDA3 in different groups and compared the differences in children's characteristics and the therapeutic effect of GH therapy between the BDA3 and no BDA3 groups.

RESULTS

A total of 752 cases were included. The overall prevalence of BDA3 was 23.1%; with a female predominance (30.8% vs. 16.1%, P < 0.01). BDA3 was more prevalent in the short stature group (27.2%) than in the normal short stature group (16.7%) and growth hormone deficiency group (16.5%). Birth length, birth weight, HtSDS, and mid-parental height of children with BDA3 were lower than those without BDA3, but there were no significant differences. In patients with Turner syndrome and idiopathic short stature, the HtSDS of the BDA3 group was significantly lower than that of the no BDA3 group (P < 0.01). During four years of GH therapy, the HtSDS improvement per year in the BDA3 group were 0.79 ± 0.29, 0.50 ± 0.31, 0.20 ± 0.30, and 0.10 ± 0.22, which were not significantly different from those in the no BDA3 group. At the end of treatment, there were no significant differences in the duration of treatment and total HtSDS improvement between these two groups.

CONCLUSIONS

BDA3 is more commonly seen in children with short stature with a female predominance. BDA3 occurrence is independent of the GH pathway and does not affect the therapeutic effect of GH on short stature children.

SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency

Inactivation mutations in the Indian hedgehog (Ihh) gene in humans cause numerous skeletal chondrodysplasias, including acrocapitofemoral dysplasia, brachydactyly type A1, and human short stature. The lack of an appropriate human-relevant model to accurately represent these chondrodysplasias has hampered the identification of clinically effective treatments. Here, we established a mouse model of human skeletal dysplasia induced by Ihh gene mutations via ablation of Ihh in Aggrecan-positive (Acan+) cells using Aggrecan (Acan)-creERT transgenic mice. Smoothen agonist (SAG) promoted Hh activity and rescued chondrocyte proliferation and differentiation by stimulating smoothened trafficking to the cilium in Ihh-silenced cells. SAG treatment corrected mouse stature and significantly decreased mortality without evidence of toxicity. Moreover, Ihh ablation in Acan+ cells produced enchondroma-like tissues near the growth plates that were significantly reduced by SAG treatment. These results demonstrated that SAG effectively treats skeletal dysplasia caused by Ihh gene mutations in a mouse model, suggesting that SAG may represent a potential drug for the treatment of these diseases and/or enchondromas.

Acrocapitofemoral dysplasia: Novel mutation in IHH in two adult patients from the third family in the literature and progression of the disease

Acrocapitofemoral dysplasia (ACFD) is a rare autosomal recessive skeletal dysplasia characterized by short stature with short limb dwarfism, brachydactyly, and a narrow thorax. Major radiographic features are egg-shaped capital femoral epiphyses with a short femoral neck and cone-shaped epiphyses, mainly in the hands and hips. To date, only four child patients from two families have been reported. We describe two adult patients with ACFD with a novel homozygous c.478C>T (p.Arg160Cys) mutation in IHH in the third family of the literature. The reported cases showed a middle phalanges which fused with distal phalanges in the fifth toes, the typical configuration of metacarpals, radial angulation and extremely short femoral neck. These findings could help the diagnosis of ACFD in adult patients. We hope that this new family will be a helpful guide for predicting and managing the prognosis of diagnosed children.

Analysis of Prevalence, Influencing Factors, and Countermeasures of Short Stature in Children and Adolescents Aged 6∼14 in Furong District, Changsha City, in 2020

In recent years, children's and adolescents' growth and development issues have received increasing attention with the socioeconomic development. The etiology of child short stature involves heredity, race, sex, nutrition, and a variety of endocrine hormones, which is very complex. The age of 6∼14 is the key period of children's development. Understanding the height characteristics, the prevalence of short stature, and its influencing factors at this stage and formulating preventive measures as soon as possible are conducive to improving the average height of children and reducing the incidence of short stature. In this study, cluster sampling was used to select 56,865 children and adolescents aged 6∼14 years old from 40 primary and secondary schools in Furong District of Changsha City, and the height of each child and adolescent was measured. The results showed that the overall crude prevalence of short stature in children aged 6∼14 in Furong District of Changsha is 2.82%. Growth hormone level <10 μg/L, pubertal retardation, familial short stature, low egg intake, and intrauterine growth retardation are independent risk factors affecting the occurrence of short stature. In order to improve the status quo of short stature of children aged 6∼14 in Furong District, Changsha City, targeted intervention should be strengthened for people with combined high risk factors.

Deletion of 2 amino acids in IHH in a Japanese family with brachydactyly type A1

BACKGROUND

Brachydactyly type A1 (BDA1) is an autosomal dominant disorder characterized by uniform shortening of the middle phalanges in all digits. It is associated with variants in the Indian Hedgehog (IHH) gene, which plays a key role in endochondral ossification. To date, heterozygous pathogenic IHH variants involving several codons, which are restricted to a specific region of the N-terminal active fragment of IHH, have been reported. The purpose of this study was to identify the pathogenic variant in a Japanese family with BDA1 and to evaluate its pathogenesis with regard to previous reports.

METHODS

The proband, a 9-year-old boy, his siblings, and his father had shortened digits and a short stature of variable severity. Based on physical examinations, radiographic findings and family history, they were diagnosed with BDA1. This family is the first case of an isolated malformation in Japan. Sanger sequencing of IHH was performed on these individuals and on the proband's unaffected mother. The significance of the variants was assessed using three-dimensional analysis methods.

RESULTS

Sanger sequencing showed a novel IHH heterozygous variant, NM_002181.4:c.544_549delTCAAAG(p.Ser182Lys183del) [NC_000002.12:g.219057461_219057466del].. These two residues are located outside the cluster region considered a hotspot of pathogenic variants. Three-dimensional modelling showed that S182 and K183 are located on the same surface as other residues associated with BDA1. Analysis of residue interactions across the interface between IHH and its interacting receptor protein revealed the presence of hydrogen bonds between them.

CONCLUSIONS

We report a novel variant, NM_002181.4:c.544_549delTCAAAG (p.Ser182Lys183del) [NC_000002.12:g.219057461_219057466del] in a Japanese family with BDA1. Indeed, neither variations in codons 182 or 183 nor with such two-amino-acid deletions in IHH have been reported previously. Although these two residues are located outside the cluster region considered a hotspot of pathogenic variants, we speculate that this variant causes BDA1 through impaired interactions between IHH and target receptor proteins in the same manner as other pathogenic variants located in the cluster region. This report expands the genetic spectrum of BDA1.

New gene discoveries in skeletal diseases with short stature

In the last decade, the widespread use of massively parallel sequencing has considerably boosted the number of novel gene discoveries in monogenic skeletal diseases with short stature. Defects in genes playing a role in the maintenance and function of the growth plate, the site of longitudinal bone growth, are a well-known cause of skeletal diseases with short stature. However, several genes involved in extracellular matrix composition or maintenance as well as genes partaking in various biological processes have also been characterized. This review aims to describe the latest genetic findings in spondyloepiphyseal dysplasias, spondyloepimetaphyseal dysplasias, and some monogenic forms of isolated short stature. Some examples of novel genetic mechanisms leading to skeletal conditions with short stature will be described. Strategies on how to successfully characterize novel skeletal phenotypes with short stature and genetic approaches to detect and validate novel gene-disease correlations will be discussed in detail. In summary, we review the latest gene discoveries underlying skeletal diseases with short stature and emphasize the importance of characterizing novel molecular mechanisms for genetic counseling, for an optimal management of the disease, and for therapeutic innovations.

Prevalence of children born small for gestational age with short stature who qualify for growth hormone treatment

BACKGROUND

Recombinant human growth hormone (rhGH) is approved in Europe as a treatment for short children born small for gestational age (SGA) since 2003. However, no study evaluated the prevalence of SGA children with short stature who qualify for rhGH in Europe so far. This study aimed to investigate in an Italian population the prevalence of children born SGA, of short stature in children born SGA, and of SGA children who qualify for rhGH treatment at 4 years of age.

METHODS

We conducted a population-based study on primary care pediatricians' databases in Trieste, Italy. Data was collected on 3769 children born between 2004 and 2014. SGA was defined as birth weight and/or birth length ≤ - 2 SDS. Data on height and weight were registered at the closest well-being visit to 1, 2, 3, 4 years of age. Short stature was defined as height ≤ - 2 SDS. Short children born SGA who qualify for rhGH treatment were identified according to Note AIFA #39 criteria (age ≥ 4 years; height ≤ - 2.5 SDS; growth velocity < 50th percentile).

RESULTS

Full data at birth were available for 3250 children. The SGA prevalence was 3.6% (0.8% SGA for weight, 2.2% SGA for length, 0.6% SGA for both weight and length). The prevalence of short stature among SGA children was 9% at 1 year of age, 6% at 2 years (significantly higher in preterm in the first 2 years), 4% at 3 years, 3% at 4 years (all born at term). At 4 years of age, median height SDS was - 0.52. One child born SGA was eligible for GH treatment (0.8% among SGA children).

CONCLUSIONS

The prevalence in a general pediatric population of children born SGA who qualify for GH treatment was 1:3250. Although the prevalence of SGA in our population was similar to previous studies, catch-up growth was recorded earlier in our sample compared to previous reports, and term babies had late catch-up. Height SDS of children born SGA at 4 years of age was lower than expected (- 0.52 SDS).

Hedgehog acyl-transferase-related multiple congenital anomalies: Report of an additional family and delineation of the syndrome

This study includes previous reports of four affected individuals from two unrelated families with hedgehog acyl-transferase (HHAT)-related multiple congenital anomaly syndrome. Microcephaly, small cerebellar vermis, holoprosencephaly, agenesis of corpus callosum, intellectual disability, short stature, skeletal dysplasia, microphthalmia-anophthalmia, and sex reversal constitute the phenotypic spectrum of this condition with variable expression. We report an additional family with three affected conceptuses: two abortuses and one living proband. We did proband-parents trio exome sequencing and identified a biallelic in-frame deletion c.365_367del; (p.Thr122del) in exon 5 of HHAT. With this report, we delineate the phenotype and allelic heterogeneity of the HHAT-related multiple congenital anomaly syndrome.

Description of four patients with TRIP11 variants expand the clinical spectrum of odontochondroplasia (ODCD) and demonstrate the existence of common variants

More than two decades since the first clinical and radiological description of odontochondroplasia (ODCD) was reported, biallelic loss of function variants in the Thyroid hormone receptor interactor 11 gene (TRIP11) were identified, the same gene implicated in the lethal disorder achondrogenesis (ACG1A). Here we report the clinical and radiological follow-up of four ODCD patients, including two siblings and an adult who interestingly has the mildest form observed to date. Four TRIP11 variants were detected, two previously unreported. Subsequently, we review the clinical and radiological findings of the 14 reported ODCD patients. The majority of ODCD patients are compound heterozygotes for TRIP11 variants, 12/14 have a null allele and a splice variant whilst one is homozygous for an in-frame splicing variant, with the splice variants resulting in residual GMAP activity and hypothesized to explain why they have ODCD and not ACG1A. However, adult patient 4 has two potentially null alleles and it remains unknown why she has very mild clinical features. The c.586C>T; p.(Gln196*) variant, previously shown by mRNA studies to result in p.Val105_Gln196del, is the most frequent variant, present in seven individuals from four families, three from different regions of the world, suggesting that it may be a variant hotspot. Another variant, c.2993_2994del; p.(Lys998Serfs*5), has been observed in two individuals with a possible common ancestor. In summary, although there are clinical and radiological characteristics common to all individuals, we demonstrate that the clinical spectrum of TRIP11-associated dysplasias is even more diverse than previously described and that common genetic variants may exist.

Growth plate gene involment and isolated short stature

PURPOSE

Short stature is a common clinical presentation, thus it is widely accepted that it is a polygenic trait. However, genome wide association and next generation sequencing studies have recently challenged this view, suggesting that many of the children classified as idiopathic short stature could instead have monogenic defects. Linear growth is determined primarily by chondrogenesis at the growth plate. This process results from chondrocyte proliferation, hypertrophy, and extracellular matrix secretion, and it is perfectly coordinated by complex networks of local paracrine and endocrine factors. Alterations in genes which control growth plate development can explain a large number of cases of isolated short stature, allowing an etiological diagnosis.

METHODS/RESULTS

We reviewed recent data on the genetic alterations in fundamental cellular processes, paracrine signaling, and cartilage matrix formation associated with impaired growth plate chondrogenesis. In particular we focused on growth plate gene involvement in nonsyndromic short stature.

CONCLUSIONS

The identification of genetic basis of growth failure will have a significant impact on the care of children affected with short stature.

Insights from the genetic characterization of central precocious puberty associated with multiple anomalies

STUDY QUESTION

Is there an (epi)genetic basis in patients with central precocious puberty (CPP) associated with multiple anomalies that unmasks underlying mechanisms or reveals novel genetic findings related to human pubertal control?

SUMMARY ANSWER

In a group of 36 patients with CPP associated with multiple phenotypes, pathogenic or likely pathogenic (epi)genetic defects were identified in 12 (33%) patients, providing insights into the genetics of human pubertal control.

WHAT IS KNOWN ALREADY

A few studies have described patients with CPP associated with multiple anomalies, but without making inferences on causalities of CPP. Genetic-molecular studies of syndromic cases may reveal disease genes or mechanisms, as the presentation of such patients likely indicates a genetic disorder.

STUDY DESIGN, SIZE, DURATION

This translational study was based on a genetic-molecular analysis, including genome-wide high throughput methodologies, for searching structural or sequence variants implicated in CPP and DNA methylation analysis of candidate regions.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A cohort of 197 patients (188 girls) with CPP without structural brain lesions was submitted to a detailed clinical evaluation, allowing the selection of 36 unrelated patients (32 girls) with CPP associated with multiple anomalies. Pathogenic allelic variants of genes known to cause monogenic CPP (KISS1R, KISS1, MKRN3 and DLK1) had been excluded in the entire cohort (197 patients). All selected patients with CPP associated with multiple anomalies (n = 36) underwent methylation analysis of candidate regions and chromosomal microarray analysis. A subset (n = 9) underwent whole-exome sequencing, due to presenting familial CPP and/or severe congenital malformations and neurocognitive abnormalities.

MAIN RESULTS AND THE ROLE OF CHANCE

Among the 36 selected patients with CPP, the more prevalent associated anomalies were metabolic, growth and neurocognitive conditions. In 12 (33%) of them, rare genetic abnormalities were identified: six patients presented genetic defects in loci known to be involved with CPP (14q32.2 and 7q11.23), whereas the other six presented defects in candidate genes or regions. In detail, three patients presented hypomethylation of DLK1/MEG3:IG-DMR (14q32.2 disruption or Temple syndrome), resulting from epimutation (n = 1) or maternal uniparental disomy of chromosome 14 (n = 2). Seven patients presented pathogenic copy number variants: three with de novo 7q11.23 deletions (Williams–Beuren syndrome), three with inherited Xp22.33 deletions, and one with de novo 1p31.3 duplication. Exome sequencing revealed potential pathogenic variants in two patients: a sporadic female case with frameshift variants in TNRC6B and AREL1 and a familial male case with a missense substitution in UGT2B4 and a frameshift deletion in MKKS.

LIMITATIONS, REASONS FOR CAUTION

The selection of patients was based on a retrospective clinical characterization, lacking a longitudinal inclusion of consecutive patients. In addition, future studies are needed, showing the long-term (mainly reproductive) outcomes in the included patients, as most of them are not in adult life yet.

WIDER IMPLICATIONS OF THE FINDINGS

The results highlighted the relevance of an integrative clinical-genetic approach in the elucidation of mechanisms and factors involved in pubertal control. Chromosome 14q32.2 disruption indicated the loss of imprinting of DLK1 as a probable mechanism of CPP. Two other chromosomal regions (7q11.23 and Xp22.33) represented new candidate loci potentially involved in this disorder of pubertal timing.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grant number 2018/03198-0 (to A.P.M.C.) and grant number 2013/08028-1 (to A.C.V.K) from the São Paulo Research Foundation (FAPESP), and grant number 403525/2016-0 (to A.C.L.) and grant number 302849/2015-7 (to A.C.L.) and grant number 141625/2016-3 (to A.C.V.K) from the National Council for Scientific and Technological Development (CNPq). The authors have nothing to disclose.

TRIAL REGISTRATION NUMBER

N/A.

Identification of the third FGF9 variant in a girl with multiple synostosis-comparison of the genotype:phenotype of FGF9 variants in humans and mice

Multiple synostosis syndrome (SYNS) is a heterogeneous group of genetic disorders mainly characterized by multiple joint synostosis due to variants in either NOG, GDF5, FGF9 or GDF6. To date, only two FGF9 variants have been associated with SYNS, characterized with hand and feet joint synostosis and fusion of the elbow and vertebral lumbar joints. Craniosynostosis was also observed in one family. Here, we report the clinical and radiological description of a young girl with a third heterozygous FGF9 variant, NM_002010.2:c.427A>T;p.(Asn143Tyr), which interestingly, is located at the same amino acid as the well characterized spontaneous Eks mouse variant. We also compare the genotype: phenotypes observed between humans and mice with SYNS.

A new approach to the diagnosis of short stature

Growth is the task of children. We review the normal process of linear growth from the fetus through adolescence and note that growth is the result of age- and gender-dependent interactions among key genetic, environmental, dietary, socioeconomic, developmental, behavioral, nutritional, metabolic, biochemical, and hormonal factors. We then define the wide range of normative data at each stage of growth and note that a pattern within this range is generally indicative of good general health and that growth significantly slower than this range may lead to growth faltering and subsequent short stature. Although not often emphasized, we detail how to properly measure infants and children because height velocity is usually determined from two height measurements (both relatively large values) to calculate the actual height velocity (a relatively much smaller number in comparison). Traditionally the physiology of growth has been taught from an endocrine-centric point-of-view. Here we review the hypothalamic-pituitary-end organ axes for the GH/IGF-1 and gonadal steroid hormones (hypothalamic-pituitary-gonadal axis), both during "mini"-puberty as well as at puberty. However, over the past few decades much more emphasis has been placed on the growth plate and its many interactions with the endocrine system but also with its own intrinsic physiology and gene mutations. These latter, whether individually (large effect size) or in combination with many others including endocrine system-based, may account in toto for meaningful differences in adult height. The clinical assessment of children with short stature includes medical, social and family history, physical exam and importantly proper interpretation of the growth curve. This analysis should lead to judicious use of screening laboratory and imaging tests depending on the pre-test probability (Bayesian inference) of a particular diagnosis in that child. In particular for those with no pathological features in the history and physical exam and a low, but normal height velocity, may lead only to a bone age exam and reevaluation (re-measurement), perhaps 6 months later. he next step depends on the comfort level of the primary care physician, the patient, and the parent; that is, whether to continue with the evaluation with more directed, more sophisticated testing, again based on Bayesian inference or to seek consultation with a subspecialist pediatrician based on the data obtained. This is not necessarily an endocrinologist. The newest area and the one most in flux is the role for genetic testing, given that growth is a complex process with large effect size for single genes but smaller effect sizes for multiple other genes which in the aggregate may be relevant to attained adult height. Genetics is a discipline that is rapidly changing, especially as the cost of exome or whole gene sequencing diminishes sharply. Within a decade it is quite likely that a genetic approach to the evaluation of children with short stature will become the standard, truncating the diagnostic odyssey and be cost effective as fewer biochemical and imaging studies are required to make a proper diagnosis.

Clinical and Molecular Description of 16 Families With Heterozygous IHH Variants

CONTEXT

Heterozygous variants in the Indian hedgehog gene (IHH) have been reported to cause brachydactyly type A1 and mild hand and feet skeletal anomalies with short stature. Genetic screening in individuals with short stature and mild skeletal anomalies has been increasing over recent years, allowing us to broaden the clinical spectrum of skeletal dysplasias.

OBJECTIVE

The objective of this article is to describe the genotype and phenotype of 16 probands with heterozygous variants in IHH.

PATIENTS AND METHODS

Targeted next-generation sequencing or Sanger sequencing was performed in patients with short stature and/or brachydactyly for which the genetic cause was unknown.

RESULTS

Fifteen different heterozygous IHH variants were detected, one of which is the first reported complete deletion of IHH. None of the patients showed the classical phenotype of brachydactyly type A1. The most frequently observed clinical characteristics were mild to moderate short stature as well as shortening of the middle phalanx on the fifth finger. The identified IHH variants were demonstrated to cosegregate with the short stature and/or brachydactyly in the 13 probands whose family members were available. However, clinical heterogeneity was observed: Two short-statured probands showed no hand radiological anomalies, whereas another 5 were of normal height but had brachydactyly.

CONCLUSIONS

Short stature and/or mild skeletal hand defects can be caused by IHH variants. Defects in this gene should be considered in individuals with these findings, especially when there is an autosomal dominant pattern of inheritance. Although no genotype-phenotype correlation was observed, cosegregation studies should be performed and where possible functional characterization before concluding that a variant is causative.

Deciphering short stature in children

Short stature is a common reason for referral to pediatric endocrinologists. Multiple factors, including genetic, prenatal, postnatal, and local environmental factors, can impair growth. The majority of children with short stature, which can be defined as a height less than 2 standard deviation score below the mean, are healthy. However, in some cases, they may have an underlying relevant disease; thus, the aim of clinical evaluation is to identify the subset of children with pathologic conditions, for example growth hormone deficiency or other hormonal abnormalities, Turner syndrome, inflammatory bowel disease, or celiac disease. Prompt identification and management of these children can prevent excessive short stature in adulthood. In addition, a thorough clinical assessment may allow evaluation of the severity of short stature and likely growth trajectory to identify the most effective interventions. Consequently, appropriate diagnosis of short stature should be performed as early as possible and personalized treatment should be started in a timely manner. An increase in knowledge and widespread availability of genetic and epigenetic testing in clinical practice in recent years has empowered the diagnostic process and appropriate treatment for short stature. Furthermore, novel treatment approaches that can be used both as diagnostic tools and as therapeutic agents have been developed. This article reviews the diagnostic approach to children with short stature, discusses the main causes of short stature in children, and reports current therapeutic approaches and possible future treatments.

A novel variant of IHH in a Chinese family with brachydactyly type 1

Background

Brachydactyly type A1(BDA-1) is an autosomal dominant disorder which is caused by heterozygous pathogenic variants in a specific region of the N-terminal active fragment of Indian Hedgehog (IHH). The disorder is mainly characterized by shortening or missing of the middle phalanges. In this study, Our purpose is to identify the pathogenic variations associated with BDA-1 involved in a five-generation Chinese family.

Methods

A BDA-1 family with 8 affected and 14 unaffected family members was recruited. Whole exome sequencing (WES) was performed to identify the pathogenic variant in the proband, and which was later confirmed and segregated by Sanger sequencing. The significance of variants were assessed using several molecular and bioinformatics analysis methods.

Results

We uncovered a novel heterozygous missense variant c.299A > G (p.D100G) at the mutational hotspot of IHH gene following whole-exome sequencing of a Chinese family with BDA-1. The variant co-segregated with BDA-1 in the pedigree, showed 100% penetrance for phalange phenotype with variable expressivity.

Conclusions

In conclusion, this study reports a five-generation Chinese family with BDA-1 due to a novel pathogenic variant (c.299A > G (p.D100G)) of IHH and expands the clinical and genetic spectrum of BDA-1.

Pathogenic variants in TNRC6B cause a genetic disorder characterised by developmental delay/intellectual disability and a spectrum of neurobehavioural phenotypes including autism and ADHD

BACKGROUND

Rare variants in hundreds of genes have been implicated in developmental delay (DD), intellectual disability (ID) and neurobehavioural phenotypes. TNRC6B encodes a protein important for RNA silencing. Heterozygous truncating variants have been reported in three patients from large cohorts with autism, but no full phenotypic characterisation was described.

METHODS

Clinical and molecular characterisation was performed on 17 patients with TNRC6B variants. Clinical data were obtained by retrospective chart review, parent interviews, direct patient interaction with providers and formal neuropsychological evaluation.

RESULTS

Clinical findings included DD/ID (17/17) (speech delay in 94% (16/17), fine motor delay in 82% (14/17) and gross motor delay in 71% (12/17) of subjects), autism or autistic traits (13/17), attention deficit and hyperactivity disorder (ADHD) (11/17), other behavioural problems (7/17) and musculoskeletal findings (12/17). Other congenital malformations or clinical findings were occasionally documented. The majority of patients exhibited some dysmorphic features but no recognisable gestalt was identified. 17 heterozygous TNRC6B variants were identified in 12 male and five female unrelated subjects by exome sequencing (14), a targeted panel (2) and a chromosomal microarray (1). The variants were nonsense (7), frameshift (5), splice site (2), intragenic deletions (2) and missense (1).

CONCLUSIONS

Variants in TNRC6B cause a novel genetic disorder characterised by recurrent neurocognitive and behavioural phenotypes featuring DD/ID, autism, ADHD and other behavioural abnormalities. Our data highly suggest that haploinsufficiency is the most likely pathogenic mechanism. TNRC6B should be added to the growing list of genes of the RNA-induced silencing complex associated with ID/DD, autism and ADHD.

Towards a Rational and Efficient Diagnostic Approach in Children Referred for Growth Failure to the General Paediatrician

Based on a recent Dutch national guideline, we propose a structured stepwise diagnostic approach for children with growth failure (short stature and/or growth faltering), aiming at high sensitivity for pathologic causes at acceptable specificity. The first step is a detailed clinical assessment, aiming at obtaining relevant clinical clues from the medical history (including family history), physical examination (emphasising head circumference, body proportions and dysmorphic features) and assessment of the growth curve. The second step consists of screening: a radiograph of the hand and wrist (for bone age and assessment of anatomical abnormalities suggestive for a skeletal dysplasia) and laboratory tests aiming at detecting disorders that can present as isolated short stature (anaemia, growth hormone deficiency, hypothyroidism, coeliac disease, renal failure, metabolic bone diseases, renal tubular acidosis, inflammatory bowel disease, Turner syndrome [TS]). We advise molecular array analysis rather than conventional karyotyping for short girls because this detects not only TS but also copy number variants and uniparental isodisomy, increasing diagnostic yield at a lower cost. Third, in case of diagnostic clues for primary growth disorders, further specific testing for candidate genes or a hypothesis-free approach is indicated; suspicion of a secondary growth disorder warrants adequate further targeted testing.

Diagnosis, Genetics, and Therapy of Short Stature in Children: A Growth Hormone Research Society International Perspective

The Growth Hormone Research Society (GRS) convened a Workshop in March 2019 to evaluate the diagnosis and therapy of short stature in children. Forty-six international experts participated at the invitation of GRS including clinicians, basic scientists, and representatives from regulatory agencies and the pharmaceutical industry. Following plenary presentations addressing the current diagnosis and therapy of short stature in children, breakout groups discussed questions produced in advance by the planning committee and reconvened to share the group reports. A writing team assembled one document that was subsequently discussed and revised by participants. Participants from regulatory agencies and pharmaceutical companies were not part of the writing process. Short stature is the most common reason for referral to the pediatric endocrinologist. History, physical examination, and auxology remain the most important methods for understanding the reasons for the short stature. While some long-standing topics of controversy continue to generate debate, including in whom, and how, to perform and interpret growth hormone stimulation tests, new research areas are changing the clinical landscape, such as the genetics of short stature, selection of patients for genetic testing, and interpretation of genetic tests in the clinical setting. What dose of growth hormone to start, how to adjust the dose, and how to identify and manage a suboptimal response are still topics to debate. Additional areas that are expected to transform the growth field include the development of long-acting growth hormone preparations and other new therapeutics and diagnostics that may increase adult height or aid in the diagnosis of growth hormone deficiency.

Achieving Optimal Short- and Long-term Responses to Paediatric Growth Hormone Therapy

It is over sixty years since the first administration of human growth hormone (GH) to children with GH deficiency, and over thirty years since recombinant human GH has been available for treatment of GH deficiency and a wider range of non-GH deficiency disorders. From a diagnostic perspective, genetic analysis, using single gene or Sanger sequencing and more recently next generation or whole exome sequencing, has brought advances in the diagnosis of specific causes of short stature, which has enabled therapy to be targeted more accurately. Genetic discoveries have ranged from defects of pituitary development and GH action to abnormalities in intracellular mechanisms, paracrine regulation and cartilage matrix formation. The strategy of GH therapy using standard doses has evolved to individualised GH dosing, depending on diagnosis and predictors of growth response. Evidence of efficacy of GH in GH deficiency, Turner syndrome and short children born small for gestational age is reviewed. The importance of critical assessment of growth response is discussed, together with the recognition and management of a poor or unsatisfactory growth response and the organisational issues related to prevention, detection and intervention regarding suboptimal adherence to GH therapy.

SHOX Deficiency in Argentinean Cohort: Long-Term Auxological Follow-Up and a Family's New Mutation

A cohort study on the growth of 19 Argentinean children, aged 0 to 18 years, and 11 of their first-degree relatives with alterations in the SHOX gene or its regulatory regions is reported. Children are born shorter and experience a growth delay during childhood with a stunted pubertal growth spurt. Body disproportion, with a sitting height/height ratio above +2 standard deviation score (SDS), was already present as early as 2 years old. Hand length was normal. Shortening of the radius, with a length below -1.9 SDS, was the earliest and most frequent radiological sign detected as early as 45 days old. We found a previously unreported mutation in a family with a highly variable phenotype, the boy had a severe phenotype with a milder presentation in other affected members of the family. We conclude that body disproportion and a shorter radius length on X-ray are useful tools for selecting children to undergo SHOX molecular studies.

Genetic causes of isolated short stature

Short stature is a common feature, and frequently remains without a specific diagnosis after conventional clinical and laboratorial evaluation. Longitudinal growth is mainly determined by genetic factors, and hundreds of common variants have been associated to height variability among healthy individuals. Although isolated short stature may be caused by the combination of variants, with a deleterious impact on the growth of individuals with polygenic inheritance, recent studies have pointed out some monogenic defects as the cause of the growth disorder observed in nonsyndromic children. The majority of these defects are in genes related to the growth plate cartilage and in the growth hormone (GH) - insulin-like growth factor 1 (IGF-1) axis. Affected patients usually present the mildest spectrum of some forms of skeletal dysplasia, or subtle abnormalities of laboratory tests, suggesting hormonal resistance or insensibility. The lack of specific characteristics, however, does not allow formulation of a definitive diagnosis without the use of broad genetic studies. Thus, molecular genetic studies including panels of genes or exome analysis will become essential in investigating and identifying the causes of isolated short stature in children, with a crucial impact on treatment and follow-up.

Multigene Sequencing Analysis of Children Born Small for Gestational Age With Isolated Short Stature

CONTEXT

Patients born small for gestational age (SGA) who present with persistent short stature could have an underlying genetic etiology that will account for prenatal and postnatal growth impairment. We applied a unique massive parallel sequencing approach in cohort of patients with exclusively nonsyndromic SGA to simultaneously interrogate for clinically substantial genetic variants.

OBJECTIVE

To perform a genetic investigation of children with isolated short stature born SGA.

DESIGN

Screening by exome (n = 16) or targeted gene panel (n = 39) sequencing.

SETTING

Tertiary referral center for growth disorders.

PATIENTS AND METHODS

We selected 55 patients born SGA with persistent short stature without an identified cause of short stature.

MAIN OUTCOME MEASURES

Frequency of pathogenic findings.

RESULTS

We identified heterozygous pathogenic or likely pathogenic genetic variants in 8 of 55 patients, all in genes already associated with growth disorders. Four of the genes are associated with growth plate development, IHH (n = 2), NPR2 (n = 2), SHOX (n = 1), and ACAN (n = 1), and two are involved in the RAS/MAPK pathway, PTPN11 (n = 1) and NF1 (n = 1). None of these patients had clinical findings that allowed for a clinical diagnosis. Seven patients were SGA only for length and one was SGA for both length and weight.

CONCLUSION

These genomic approaches identified pathogenic or likely pathogenic genetic variants in 8 of 55 patients (15%). Six of the eight patients carried variants in genes associated with growth plate development, indicating that mild forms of skeletal dysplasia could be a cause of growth disorders in this group of patients.

Genetic regulation of linear growth

Linear growth occurs at the growth plate. Therefore, genetic defects that interfere with the normal function of the growth plate can cause linear growth disorders. Many genetic causes of growth disorders have already been identified in humans. However, recent genome-wide approaches have broadened our knowledge of the mechanisms of linear growth, not only providing novel monogenic causes of growth disorders but also revealing single nucleotide polymorphisms in genes that affect height in the general population. The genes identified as causative of linear growth disorders are heterogeneous, playing a role in various growth-regulating mechanisms including those involving the extracellular matrix, intracellular signaling, paracrine signaling, endocrine signaling, and epigenetic regulation. Understanding the underlying genetic defects in linear growth is important for clinicians and researchers in order to provide proper diagnoses, management, and genetic counseling, as well as to develop better treatment approaches for children with growth disorders.

Growth hormone therapy in children; research and practice - A review

Short stature remains the most common reason for referral to a pediatric Endocrinologist and its management remains a challenge. One of the main controversies is the diagnosis of idiopathic short stature and the role of new technologies for genetic investigation of children with inadequate growth. Complexities in management of children with short stature includes selection of who should receive interventions such as recombinant human growth hormone, and how should this agent dose be adjusted during treatment. Should anthropometrical data be the primary determinant or should biochemical and genetic data be used to improve growth response and safety? Furthermore, what is considered a suboptimal response to growth hormone therapy and how should this be managed? Treatment of children with short stature remains a "hot" topic and more data is needed in several areas. These issues are reviewed in this paper.

Genetics of Growth Disorders-Which Patients Require Genetic Testing?

The second 360° European Meeting on Growth Hormone Disorders, held in Barcelona, Spain, in June 2017, included a session entitled Pragmatism vs. Curiosity in Genetic Diagnosis of Growth Disorders, which examined current concepts of genetics and growth in the clinical setting, in terms of both growth failure and overgrowth. For patients with short stature, multiple genes have been identified that result in GH deficiency, which may be isolated or associated with additional pituitary hormone deficiencies, or in growth hormone resistance, primary insulin-like growth factor (IGF) acid-labile subunit deficiency, IGF-I deficiency, IGF-II deficiency, IGF-I resistance, and primary PAPP-A2 deficiency. While genetic causes of short stature were previously thought to primarily be associated with the GH-IGF-I axis, it is now established that multiple genetic anomalies not associated with the GH-IGF-I axis can result in short stature. A number of genetic anomalies have also been shown to be associated with overgrowth, some of which involve the GH-IGF-I axis. In patients with overgrowth in combination with an intellectual disability, two predominant gene families, the epigenetic regulator genes, and PI3K/AKT pathway genes, have now been identified. Specific processes should be followed for decisions on which patients require genetic testing and which genes should be examined for anomalies. The decision to carry out genetic testing should be directed by the clinical process, not merely for research purposes. The intention of genetic testing should be to direct the clinical options for management of the growth disorder.

Children Born Small for Gestational Age: Differential Diagnosis, Molecular Genetic Evaluation, and Implications

Children born small for gestational age (SGA), defined as a birth weight and/or length below -2 SD score (SDS), comprise a heterogeneous group. The causes of SGA are multifactorial and include maternal lifestyle and obstetric factors, placental dysfunction, and numerous fetal (epi)genetic abnormalities. Short-term consequences of SGA include increased risks of hypothermia, polycythemia, and hypoglycemia. Although most SGA infants show catch-up growth by 2 years of age, ∼10% remain short. Short children born SGA are amenable to GH treatment, which increases their adult height by on average 1.25 SD. Add-on treatment with a gonadotropin-releasing hormone agonist may be considered in early pubertal children with an expected adult height below -2.5 SDS. A small birth size increases the risk of later neurodevelopmental problems and cardiometabolic diseases. GH treatment does not pose an additional risk.

New developments in the genetic diagnosis of short stature

PURPOSE OF REVIEW

Genome-wide approaches including genome-wide association studies as well as exome and genome sequencing represent powerful new approaches that have improved our ability to identify genetic causes of human disorders. The purpose of this review is to describe recent advances in the genetic causes of short stature.

RECENT FINDINGS

In addition to SHOX deficiency which is one of the most common causes of isolated short stature, PAPPA2, ACAN, NPPC, NPR2, PTPN11 (and other rasopathies), FBN1, IHH and BMP2 have been identified in isolated growth disorders with or without other mild skeletal findings. In addition, novel genetic causes of syndromic short stature have been discovered, including pathogenic variants in BRCA1, DONSON, AMMECR1, NFIX, SLC25A24, and FN1.

SUMMARY

Isolated growth disorders are often monogenic. Specific genetic causes typically have specific biochemical and/or phenotype characteristics which are diagnostically helpful. Identification of additional subjects with a specific genetic cause of short stature often leads to a broadening of the known clinical spectrum for that condition. The identification of novel genetic causes of short stature has provided important insights into the underlying molecular mechanisms of growth failure.