Novel aggrecan variant, p. Gln2364Pro, causes severe familial nonsyndromic adult short stature and poor growth hormone response in Chinese children

Treatment of Short Stature in Aggrecan-deficient Patients With Recombinant Human GH: 3-year Response

Context

Patients with aggrecan (ACAN) deficiency present with dominantly inherited short stature, as well as early-onset joint disease.

Objective

The objective of this study was to evaluate the efficacy and safety of recombinant human GH (rhGH) on linear growth in ACAN-deficient children.

Methods

Open-label, single-arm, prospective study over 3 years recruiting 10 treatment-naïve patients with heterozygous mutations in ACAN, age ≥2 years, prepubertal, and normal IGF-I concentration. Patients were treated with rhGH (initially, 50 mcg/kg/day). Main outcomes were change in (Δ) height SD score (HtSDS) and height velocity (HV).

Results

Ten patients (6 females) enrolled with median chronological age (CA) of 5.6 years (range, 2.4-9.7). Baseline median HtSDS, HV, and bone age/CA were -2.5 (range, -4.3 to -1.1), 5.2 cm/year (range, 3.8 to 7.1), and 1.2 (range, 0.9 to 1.5), respectively. The cumulative median ΔHtSDS over 3 years was +1.21 (range, +0.82 to +1.94). Median HV increased to 8.3 cm/year (range, 7.3-11.2), 7.7 cm/year (range, 5.9-8.8), and 6.8 cm/year (range, 4.9-8.6) during years 1, 2, and 3, respectively. The median Δ predicated adult height was +6.8 cm over 3 years. Four female subjects entered puberty; nevertheless, median Δbone age/CA was -0.1. No adverse events related to rhGH were observed.

Conclusion

Linear growth improved in a cohort of ACAN-deficient patients treated with rhGH, albeit somewhat attenuated in older participants who entered puberty. Longitudinal follow-up is needed to assess the long-term efficacy of rhGH and adult height outcome.

A rare case of skeletal dysplasia: biallelic variant in ACAN gene

OBJECTIVES

Spondylo-epimetaphyseal dysplasia-aggregan (SEMD-ACAN) is a rare form of osteo-chondrodysplasia that includes vertebral, epiphyseal and metaphyseal dysplasia. It occurs as a result of loss-of-function mutations in the ACAN gene, which encodes aggregan protein, which is the basic component of the extracellular matrix in cartilage. It results in disproportionately short stature and skeletal abnormalities. Here, we aimed to present the fourth SEMD-ACAN report in the literature.

CASE PRESENTATION

A 9-year-old girl was admitted to our clinic with growth retardation. She was born from a first-degree cousin marriage with severe short stature (41 cm; -3.54 SDS). Her mother also had severe short stature. Her height was 110 cm (-4.6 SDS); she had midface hypoplasia, low-set ears, short neck, short limbs, and central obesity. Biochemical and hormonal tests were normal. Skeletal survey showed moderate platyspondylia, thoracolumbar scoliosis, lumbar lordosis, bilateral femoro-acetabular narrowing, and advanced bone age (10 years). The patient's brother was 100 cm (-3.97 SDS). He had similar but milder clinical findings. Biallelic ACAN variation (c.512C>T; p. Ala171Val) was detected in two siblings by next-generation sequencing. The parents were heterozygous carriers. Before, the heterozygous form of this variant has been reported in a 15-year-old boy with short stature, advanced bone age, and dysmorphic features.

CONCLUSIONS

SEMD-ACAN is a rare genetic condition that affects bone growth and development and can cause physical and developmental abnormalities. This article highlights the importance of considering genetic testing in characteristic symptoms associated with SEMD-ACAN, such as severe growth retardation and skeletal abnormalities.

Downregulation of ACAN is Associated with the Growth hormone pathway and Induces short stature

BACKGROUND

ACAN heterozygous mutations can cause short stature in patients with or without advanced bone age and have recently attracted researchers' attention. Growth hormone can be used to treat short stature induced by ACAN mutations; however, few studies have focused on the underlying mechanism of this treatment.

METHODS

Four patients with new mutations were reported based on clinical data and genetic tests. We investigated the expression and Gene Ontology biological process enrichment of ACAN and GH pathways based on GTEx databases through bioinformatics analyses. The effect of ACAN on the growth hormone response evaluated in ATDC5 cells with a growth hormone stimulation test.

RESULTS

Four mutations were reported in this study: c.619C > A, c.1967A > G, c.1888G > A, and c.1308_1309del. All patients' heights were under -2.5 SD, with one had advanced bone age, and two had GH deficiency. Two individuals received growth hormone therapy acquired variable levels of height SD score improvement. ACAN and the GH pathway were strongly associated; ACAN does not affect GHR but regulates the response to GH. Downregulating ACAN inhibited ATDC5 cell proliferation induced by GH.

CONCLUSION

ACAN is associated with the GH pathway, revealing the potential mechanism underlying GH-targeted treatment for ACAN mutation-induced short stature. GH-promoting therapies may increase patients' heights.

Case report: A novel heterozygous frameshift mutation of ACAN in a Chinese family with short stature and advanced bone age

Short stature (OMIM: 165800) is a common pediatric disorder. Any abnormality in the cartilage formation of the growth plate can cause short stature. Aggrecan, encoded by ACAN, is an important component of the extracellular matrix. Mutations in ACAN have been reported to cause short stature. In the present study, we enrolled a Chinese family with short stature and advanced bone age across three generations. Whole-exome sequencing (WES) was performed on the proband to detect the candidate genes causing short stature in family. A novel heterozygous frameshift mutation (NM_013227.3:c.7230delT; NP_001356197.1: p. Phe2410Leufs*9) of the ACAN gene was confirmed to be a genetic lesion in this family. This variant, which was located in a functional site globular 3 (G3) domain of ACAN and predicted to be deleterious by informatics programs, was co-segregated with the affected family members by performing Sanger sequencing. Literatures review of growth hormone (GH) treatment outcome of all previously reported ACAN patients suggesting that the G3 domain of ACAN may be critical in the development of short stature and growth hormone treatment. These findings not only contribute to the genetic diagnosis and counseling of the family, but will also expand the mutation spectrum of ACAN.

The Spectrum of ACAN Gene Mutations in a Selected Chinese Cohort of Short Stature: Genotype-Phenotype Correlation

Objective: Mutations in the ACAN gene have been reported to cause short stature. However, the prevalence estimates of pathogenic ACAN variants in individuals with short stature vary, and the correlation between ACAN genotype and clinical phenotype remain to be evaluated. To determine the prevalence of ACAN variants among Chinese people with short stature and analyze the relationship between genotype and main clinical manifestations of short stature and advanced bone age among patients with ACAN variants.

Methods: We performed next-generation sequencing-based genetic analyses on 442 individuals with short stature. ACAN variants were summarized, previously reported cases were retrospectively analyzed, and an association analysis between genotype and phenotype was conducted.

Result: We identified 15 novel and two recurrent ACAN gene variants in 16 different pedigrees that included index patients with short stature. Among the patients with ACAN variants, 12 of 18 had advanced bone age and 7 of 18 received growth hormone therapy, 5 (71.4%) of whom exhibited variable levels of height standard deviation score improvement. Further analysis showed that patients with ACAN truncating variants had shorter height standard deviation scores (p = 0.0001) and larger bone age–chronological age values (p = 0.0464). Moreover, patients in this Asian population had a smaller mean bone age–chronological age value than those that have been determined in European and American populations (p = 0.0033).

Conclusion: Our data suggest that ACAN mutation is a common cause of short stature in China, especially among patients with a family history of short stature but also among those who were born short for their gestational age without a family history. Patients with truncating variants were shorter in height and had more obvious advanced bone age, and the proportion of patients with advanced bone age was lower in this Asian population than in Europe and America.

Treatment of Short Stature in Aggrecan-deficient Patients With Recombinant Human Growth Hormone: 1-Year Response

CONTEXT

Patients with aggrecan (ACAN) deficiency present with dominantly inherited short stature, often with advanced skeletal maturation and premature growth cessation. There is a paucity of information on the effects of growth-promoting interventions.

OBJECTIVE

The aim of this study was to evaluate the efficacy and safety of recombinant human growth hormone (rhGH) therapy on linear growth in children with ACAN deficiency.

METHODS

Open-label, single-arm, prospective study at Cincinnati Children's Hospital Medical Center. Ten treatment-naïve patients were recruited. Inclusion criteria were a confirmed heterozygous mutation in ACAN, age ≥2 years, prepubertal, bone age (BA) ≥chronological age (CA), and normal insulin-like growth factor I concentration. Treatment was with rhGH (50 µg/kg/day) over 1 year. Main outcomes measured were height velocity (HV) and change in (Δ) height SD score (HtSDS).

RESULTS

Ten patients (6 females) were enrolled with median CA of 5.6 years (range 2.4-9.7). Baseline median HtSDS was -2.5 (range -4.3 to -1.1). Median baseline BA was 6.9 years (range 2.5-10.0), with median BA/CA of 1.2 (range 0.9-1.5). Median pretreatment HV was 5.2 cm/year (range 3.8-7.1), increased to 8.3 cm/year (range 7.3-11.2) after 1 year of therapy (P = .004). Median ΔHtSDS after 1 year was +0.62 (range +0.35 to +1.39) (P = .002). Skeletal maturation did not advance inappropriately (median ΔBA/CA -0.1, P = .09). No adverse events related to rhGH were observed.

CONCLUSION

Treatment with rhGH improved linear growth in a cohort of patients with short stature due to ACAN deficiency.

Novel missense ACAN gene variants linked to familial osteochondritis dissecans cluster in the C-terminal globular domain of aggrecan

The cartilage aggrecan proteoglycan is crucial for both skeletal growth and articular cartilage function. A number of aggrecan (ACAN) gene variants have been linked to skeletal disorders, ranging from short stature to severe chondrodyplasias. Osteochondritis dissecans is a disorder where articular cartilage and subchondral bone fragments come loose from the articular surface. We previously reported a missense ACAN variant linked to familial osteochondritis dissecans, with short stature and early onset osteoarthritis, and now describe three novel ACAN gene variants from additional families with this disorder. Like the previously described variant, these are autosomal dominant missense variants, resulting in single amino acid residue substitutions in the C-type lectin repeat of the aggrecan G3 domain. Functional studies showed that neither recombinant variant proteins, nor full-length variant aggrecan proteoglycan from heterozygous patient cartilage, were secreted to the same level as wild-type aggrecan. The variant proteins also showed decreased binding to known cartilage extracellular matrix ligands. Mapping these and other ACAN variants linked to hereditary skeletal disorders showed a clustering of osteochondritis dissecans-linked variants to the G3 domain. Taken together, this supports a link between missense ACAN variants affecting the aggrecan G3 domain and hereditary osteochondritis dissecans.

Clinical phenotype and musculoskeletal characteristics of patients with aggrecan deficiency

Aggrecan is a proteoglycan within the physeal and articular cartilage. Aggrecan deficiency, due to heterozygous mutations in the ACAN gene, causes dominantly inherited short stature and, in many patients, early-onset osteoarthritis and degenerative disc disease. We aimed to further characterize this phenotypic spectrum with an emphasis on musculoskeletal health. Twenty-two individuals from nine families were enrolled. Histories and examinations focused on joint health, gait analysis, joint specific patient reported outcomes, and imaging studies were performed. All patients had dominantly inherited short stature, with the exception of a de novo mutation. Short stature was worse in adults versus children (median height -3.05 SD vs. -2.25 SD). ACAN mutations were not always associated with bone age advancement (median advancement +1.1 years, range 0 to +2 years). Children had subtle disproportionality and clinically silent joint disease-25% with osteochondritis dissecans (OD). Adults had a high prevalence of joint symptomatology-decline in knee function, disability from spinal complaints, and lower physical activity on outcome measures. Osteoarthritis (OA) and OD was detected in 90% of adults, and orthopedic surgeries were reported in 60%. Aggrecan deficiency leads to short stature with progressive decline in height SD, mild skeletal dysplasia, and increasing prevalence of joint pathology over time. Optimal musculoskeletal health and quality of life can be attained with timely identification of pathology and intervention.

Description of the molecular and phenotypic spectrum in Chinese patients with aggrecan deficiency: Novel ACAN heterozygous variants in eight Chinese children and a review of the literature

OBJECTIVE

This study analyzed eight Chinese short stature children with aggrecan deficiency, and aimed to investigate potential genotype-phenotype correlations, differences in clinical characteristics between the Chinese and the Western populations, and effectiveness of recombinant human growth hormone therapy in patients with ACAN variants through a review of the literature.

METHODS

Pediatric short stature patients with ACAN heterozygous variants were identified using whole-exome sequencing. Subsequently, a literature review was carried out to summarize the clinical features, genetic findings, and efficacy of growth-promoting therapy in patients with ACAN variants.

RESULTS

We identified seven novel ACAN mutations and one recurrent variant. Patients in our center manifested with short stature (average height SDS: -3.30 ± 0.85) with slight dysmorphic characteristics. The prevalence of dysmorphic features in the Chinese populations is significantly lower than that in the Western populations. Meanwhile, only 24.24% of aggrecan-deficient Chinese children showed significantly advanced bone age (BA). Promising therapeutic benefits were seen in the patients who received growth-promoting treatment, with an increase in growth velocity from 4.52 ± 1.00 cm/year to 8.03 ± 1.16 cm/year.

CONCLUSION

This study further expanded the variation spectrum of the ACAN gene and demonstrated that Chinese children with short stature who carried ACAN heterozygous variants exhibited early growth cessation, which may remain unnoticed by clinicians as most of these children had very mild dysmorphic characteristics and showed BA that was consistent with the chronological age. Genetic testing may help in the diagnosis.

Evaluation of Growth Hormone Therapy in Seven Chinese Children With Familial Short Stature Caused by Novel ACAN Variants

OBJECTIVE

ACAN gene variants are an important cause of familial short stature (FSS). Appropriate growth-promoting therapies effectively improve the patient height. Here, we report a therapeutic assessment of cases of seven families of FSS patients with heterozygous ACAN variants. Our findings provide a valuable theoretical basis for the clinical diagnosis and treatment of this disease.

METHODS

From December 2020 to June 2021, 32 FSS patients were examined in Tianjin Medical University General Hospital (Tianjin, China) by whole-exome sequencing to determine whether ACAN variants were present. Their clinical data were summarized and scrupulously analyzed.

RESULTS

We found seven novel heterozygous ACAN variants: c.1051 + 2T > A, c.313T > C (p.S105P), c.2660C > G (p.S887X), c.2153C > A (p. T718K), c.7243delG (p.D2415Tfs^*4), c.2911G > T (p.G971X), c.758-7T > C. All seven patients had proportionate short stature and mild skeletal dysplasia. Endocrine examination results were normal. Only one of the patients had an advanced bone age (1.1 years older than chronological age), whereas the other patients had normal bone ages. All of them had a family history of short stature, with or without osteoarthritis or intervertebral disc disease. All seven patients accepted treatment with recombinant human growth hormone (rhGH) and were regularly followed up. One patient did not come at the follow-up visit. The height of the remaining six patients before and after the treatment was -2.89 ± 0.68 SDS, -1.91 ± 0.93 SDS, respectively, with a treatment course of 1.85 ± 1.91 years. A good therapeutic response was observed in all of them.

CONCLUSIONS

In this study, seven novel heterozygous variants in ACAN were discovered, which expanded the spectrum of the already established ACAN pathogenic variants. In FSS cohort, the proportion of ACAN variants accounted was large. The treatment with rhGH effectively increased the patient height, but further studies with longer follow-up periods and more extensive observations are required to elucidate the long-term effect.

Identification of novel ACAN mutations in two Chinese families and genotype-phenotype correlation in patients with 74 pathogenic ACAN variations

Background

ACAN (OMIM 155760) is located on chromosome 15q26 and encodes the production of aggrecan. Aggrecan is a large chondroitin sulfate proteoglycan with a molecular weight of 254 kDa and contains 2530 amino acids. It is a critical structural component of the extracellular matrix of cartilage, including growth plate, articular, and intervertebral disk cartilage. It plays a key role in bone development.

Methods

Here, we describe two pedigrees with loss‐of‐function variants in ACAN. Whole exome sequencing was performed for the probands from each family. We illustrate the clinical variability associated with ACAN variants.

Results

The proband of pedigree A manifested short stature, relative macrocephaly, mild flat nasal bridge, low‐set ears, short neck, and short thumbs. The proband of pedigree B had short height, abnormal vertebral development, and central precocious puberty. By trio‐based whole exome sequencing and in silico analyses, we identified two de novo heterozygous variants of ACAN: NM_013227.4: c.116dupT, p.Arg40Glufs*51 and NM_013227.4: c.2367delC, p.Ser790Glnfs*20 (accession number: AC103982.10).

Conclusion

The clinical manifestations of ACAN gene variants are diverse. ACAN gene variants are important genetic factors for short stature and should be considered as the differential diagnosis of children with idiopathic short stature (ISS).

Retrospective Diagnosis of a Novel ACAN Pathogenic Variant in a Family With Short Stature: A Case Report and Review of the Literature

Short stature is a frequent disorder in the pediatric population and can be caused by multiple factors. In the last few years, the introduction of Next Generation Sequencing (NGS) in the molecular diagnostic workflow led to the discovery of mutations in novel genes causing short stature including heterozygous mutations in ACAN gene. It encodes for aggrecan, a primary proteoglycan component specific for the structure of the cartilage growth plate, articular and intervertebral disc. We report a novel ACAN heterozygous pathogenic variant in a family with idiopathic short stature, early-onset osteoarthritis and osteoarthritis dissecans (SSOAOD). We also performed a literature review summarizing the clinical characteristic of ACAN's patients. The probands are two Caucasian sisters with a family history of short stature and osteoarthritis dissecans. They showed dysmorphic features such as mild midface hypoplasia, brachydactyly and broad thumbs, especially the great toes. The same phenotype was presented in the mother who had had short stature and suffered from intervertebral disc disease. DNA sequencing identified a heterozygous pathogenic variation (c.4390delG p.Val1464Ter) in the sisters, with a maternal inheritance. The nonsense mutation, located on exon 12, results in premature truncation and presumed loss of protein function. In terms of treatment, our patients underwent recombinant human growth hormone replacement therapy, associated with gonadotropin releasing hormone therapy, in order to block early growth cessation and therefore reach a better final height. Our case suggests that SSOAOD ACAN related should be considered in the differential diagnosis of children with autosomal dominant short stature and family history of joints disease.

A High Proportion of Novel ACAN Mutations and Their Prevalence in a Large Cohort of Chinese Short Stature Children

CONTEXT

Aggrecan, encoded by the ACAN gene, is the main proteoglycan component in the extracellular cartilage matrix. Heterozygous mutations in ACAN have been reported to cause idiopathic short stature. However, the prevalence of ACAN pathogenic variants in Chinese short stature patients and clinical phenotypes remain to be evaluated.

OBJECTIVE

We sought to determine the prevalence of ACAN pathogenic variants among Chinese short stature children and characterize the phenotypic spectrum and their responses to growth hormone therapies.

PATIENTS AND METHODS

Over 1000 unrelated short stature patients ascertained across China were genetically evaluated by next-generation sequencing-based test.

RESULT

We identified 10 novel likely pathogenic variants and 2 recurrent pathogenic variants in this cohort. None of ACAN mutation carriers exhibited significant dysmorphic features or skeletal abnormities. The prevalence of ACAN defect is estimated to be 1.2% in the whole cohort; it increased to 14.3% among those with advanced bone age and to 35.7% among those with both advanced bone age and family history of short stature. Nonetheless, 5 of 11 ACAN mutation carries had no advanced bone age. Two individuals received growth hormone therapy with variable levels of height SD score improvement.

CONCLUSION

Our data suggest that ACAN mutation is 1 of the common causes of Chinese pediatric short stature. Although it has a higher detection rate among short stature patients with advanced bone age and family history, part of affected probands presented with delayed bone age in Chinese short stature population. The growth hormone treatment was moderately effective for both individuals.

Growth-Promoting Therapies May Be Useful In Short Stature Patients With Nonspecific Skeletal Abnormalities Caused By Acan Heterozygous Mutations: Six Chinese Cases And Literature Review

OBJECTIVE

There are numerous reasons for short stature, including mutations in osteochondral development genes. ACAN, one such osteochondral development gene in which heterozygous mutations can cause short stature, has attracted attention from researchers in recent years. Therefore, we analyzed six cases of short stature with heterozygous ACAN mutations and performed a literature review.

METHODS

Clinical information and blood samples from 6 probands and their family members were collected after consent forms were signed. Gene mutations in the probands were detected by whole-exome sequencing. Then, we searched the literature, performed statistical analyses, and summarized the characteristics of all reported cases.

RESULTS

We identified six novel mutations in ACAN: c.1411C>T, c.1817C>A, c.1762C>T, c.2266G>C, c.7469G>A, and c.1733-1G>A. In the literature, more than 200 affected individuals have been diagnosed genetically with a similar condition (height standard deviation score [SDS] -3.14 ± 1.15). Among affected individuals receiving growth-promoting treatment, their height before and after treatment was SDS -2.92±1.07 versus SDS -2.14±1.23 (P<.001). As of July 1, 2019, a total of 57 heterozygous ACAN mutations causing nonsyndromic short stature had been reported, including the six novel mutations found in our study. Approximately half of these mutations can lead to protein truncation.

CONCLUSIONS

This study used clinical and genetic means to examine the relationship between the ACAN gene and short stature. To some extent, clear diagnosis is difficult, since most of these affected individuals' characteristics are not prominent. Growth-promoting therapies may be beneficial for increasing the height of affected patients.

ABBREVIATIONS

AI = aromatase inhibitor; ECM = extracellular matrix; GnRHa = gonadotropin-releasing hormone analogue; IQR = interquartile range; MIM = Mendelian Inheritance in Man; PGHD = partial growth hormone deficiency; rhGH = recombinant human growth hormone; SDS = standard deviation score; SGA = small for gestational age; SGHD = severe growth hormone deficiency.

Aggrecan, the Primary Weight-Bearing Cartilage Proteoglycan, Has Context-Dependent, Cell-Directive Properties in Embryonic Development and Neurogenesis: Aggrecan Glycan Side Chain Modifications Convey Interactive Biodiversity

This review examines aggrecan's roles in developmental embryonic tissues, in tissues undergoing morphogenetic transition and in mature weight-bearing tissues. Aggrecan is a remarkably versatile and capable proteoglycan (PG) with diverse tissue context-dependent functional attributes beyond its established role as a weight-bearing PG. The aggrecan core protein provides a template which can be variably decorated with a number of glycosaminoglycan (GAG) side chains including keratan sulphate (KS), human natural killer trisaccharide (HNK-1) and chondroitin sulphate (CS). These convey unique tissue-specific functional properties in water imbibition, space-filling, matrix stabilisation or embryonic cellular regulation. Aggrecan also interacts with morphogens and growth factors directing tissue morphogenesis, remodelling and metaplasia. HNK-1 aggrecan glycoforms direct neural crest cell migration in embryonic development and is neuroprotective in perineuronal nets in the brain. The ability of the aggrecan core protein to assemble CS and KS chains at high density equips cartilage aggrecan with its well-known water-imbibing and weight-bearing properties. The importance of specific arrangements of GAG chains on aggrecan in all its forms is also a primary morphogenetic functional determinant providing aggrecan with unique tissue context dependent regulatory properties. The versatility displayed by aggrecan in biodiverse contexts is a function of its GAG side chains.