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Article

Molecular Basis for Hypochondroplasia in Japan

1
Growth Hormone Treatment Study Committee, The Foundation for Growth Science, Tokyo 113-0033, Japan
2
Department of Pediatrics, Keio University School of Medicine, Tokyo 160-8582, Japan
3
Department of Pediatrics, Niigata University Medical and Dental Hospital, Niigata 951-8520, Japan
4
Department of Pediatrics, Tomakomai City Hospital, Tomakomai 053-8567, Japan
5
Department of Pediatrics, Tokyo-Kita Medical Center, Tokyo 114-0033, Japan
6
Department of Medical Genetics, Shinshu University School of Medicine, Nagano 390-8621, Japan
7
Center for Medical Genetics, Shinshu University Hospital, Nagano 390-8621, Japan
8
Department of Genetics and Genomics, Kitasato University Hospital, Sagamihara 252-0329, Japan
9
Department of Radiology, Musashino Yohwakai Hospital, Tokyo 180-0012, Japan
*
Author to whom correspondence should be addressed.
Endocrines 2022, 3(3), 428-432; https://doi.org/10.3390/endocrines3030034
Submission received: 15 May 2022 / Revised: 22 June 2022 / Accepted: 19 July 2022 / Published: 22 July 2022
(This article belongs to the Section Pediatric Endocrinology and Growth Disorders)

Abstract

:
Hypochondroplasia is an autosomal dominant genetic disorder due to a heterozygous pathogenic variant of the FGFR3 gene. The early diagnosis of hypochondroplasia is necessary, since growth hormone is effective for improving adult height. The genetic test for the FGFR3 gene could help the early diagnosis. The detailed characteristics of FGFR3 genotypes have not been widely investigated in Japan, except for a common pathogenic variant, p.Asn540Lys. This study retrospectively analyzed the FGFR3 genotypes of 35 patients from 30 families with hypochondroplasia (age, range 0–6 years, median 1 year) in Japan. The pathogenic variants of FGFR3 were identified in all the patients: p.Asn540Lys in 23 probands (76.7%), p.Lys650Gln in 2 (6.7%), p.Leu324His in 2 (6.7%), p.Leu324Val, p.Ser351Cys, and p.Lys650Thr in 1 each (3.2%). The median age at diagnosis, height SD score at diagnosis, or the severity of radiologic findings was not significantly different between probands with p.Asn540Lys and those with other variants. Intellectual disability or epilepsy was identified in seven patients with p.Asn540Lys, but none with other variants. The genetic test of FGFR3 can be useful for assessing the potential risk of neurological sequela in children with hypochondroplasia.

1. Introduction

Hypochondroplasia (HCH) is an autosomal dominant genetic disorder of bone dysplasia, characterized by disproportionate short stature with rhizomelic shortening of the limbs. HCH is caused by a heterozygous pathogenic variant of FGFR3 that constitutionally activates the signaling pathway of fibroblast growth factor receptor 3 [1]. The early diagnosis of HCH is necessary, since growth hormone is effective for improving adult height [2]. The genetic test for FGFR3 could help the early diagnosis of HCH. However, the possible role of FGFR3 genotyping in the diagnosis of HCH has not been clarified.
Pathogenic variants in FGFR3 are responsible for a group of bone dysplasia, including thanatophoric dysplasia, achondroplasia, or HCH [3]. The genotype–phenotype relationship in the FGFR3-related disorders is clear. Each FGFR3 genotype corresponds to each disorder without overlap [4]. p.Asn540Lys in FGFR3 is the most common pathogenic variant for HCH and is observed in 50–70% of the cases [1,5,6]. The variation and rarity of other variants preclude detailed investigation. There is no comprehensive study determining FGFR3 genotype in a large number of patients with HCH. Thus, the genotype–phenotype relationship in HCH has not been fully understood. This study conducted a molecular investigation on 35 Japanese patients with HCH to define the role of the genetic test in the clinical management of HCH.

2. Materials and Methods

2.1. Study Subjects

This study retrospectively investigated 35 patients with HCH from 22 institutions in all regions of Japan. Thirty-one were offered for genetic analysis of FGFR3 to the Department of Pediatrics, Keio University School of Medicine, and four were provided from the database of the Foundation for Growth Science. Four families with affected mothers and their offspring were included. All the patients were clinically diagnosed as HCH based on rhizomelic short stature and characteristic radiologic findings. The characteristic radiologic findings were assessed by an expert radiologist (G.N.). Clinical information of the patients was collected such as birth length and weight, development, epilepsy, or brain MRI. Three patients (Cases 4, 5, and 9) were already reported previously [7,8]. The study collected the clinical data of each patient including the age and height at diagnosis, the presence or absence of intellectual disability or epilepsy, and brain MRI findings.

2.2. FGFR3 Genotype

We collected genomic DNA samples from the 31 patients who were offered for the genetic analysis. Genomic DNA was extracted from peripheral white blood cells. We examined all coding exons and flanking introns of FGFR3 by Sanger sequencing. Primer sequences and PCR conditions are available upon request. This study was approved by the Ethics Committee of Keio University School of Medicine and the Ethics Committee of Tokyo Metropolitan Children’s Medical Center. We obtained written informed consent for molecular studies from the parents. The FGFR3 genotypes of the other four patients were provided directly from the database of the Foundation for Growth Science.

3. Results

Heterozygous missense variants of FGFR3 were observed in all the 35 patients with HCH (Table 1). The variants were p.Asn540Lys in 23 families (76.7%), p.Lys650Gln in 2 (6.7%), p.Leu324His in 2 (6.7%), p.Leu324Val in 1 each (3.2%), p.Ser351Cys in 1 each (3.2%), and p.Lys650Thr in 1 (3.2%). These six variants were previously reported as pathogenic [9]. The severity of radiologic findings was not significantly different between probands with p.Asn540Lys and those with other variants.
The age and height SD score at diagnosis in probands were plotted in Figure 1. The median age at diagnosis in probands was 2 years, ranging from 0 to 6 years. The median height SD score at diagnosis in probands was −3.1, ranging from −5.6 to −0.3. The height SD scores at diagnosis were below −2.0 SD in all the patients, except in two cases diagnosed at 4 months of age or younger (Case 27, −0.6 SD at 4 months of age; Case 31, −0.3 SD in the neonatal period). The median age or height SD score at diagnosis was not significantly different between probands with p.Asn540Lys (n = 23) and those with other variants (n = 7) (p = 0.635 or 0.649, respectively).
At least seven patients had intellectual disability or epilepsy. Temporal lobe dysgenesis was confirmed in two out of four patients with intellectual disability and two out of four with epilepsy who underwent a brain MRI scan.

4. Discussion

This study reported FGFR3 genotypes of 35 Japanese patients who were radiologically and genetically confirmed as having HCH. All 33 patients diagnosed older than 4 months of age had a height SD score less than −2.0 SD, resembling the finding of achondroplasia that short stature becomes evident during infancy [10]. Radiologic findings become evident even before decreased growth velocity. In fact, Saito et al. reported that radiological clues are useful to diagnose HCH in the neonatal period [8]. The early detection of patients was possibly explained by the expertise in diagnostic radiology. Despite a possible selection bias, these data can be helpful to reveal genotypic or phenotypic features of HCH in Japan.
p.Asn540Lys has been reported as the most prevalent pathogenic variant among different ethnicities [5,6]. The results from this study are consistent with those of previous studies, showing that p.Asn540Lys was observed in 76.7% of HCH. Rousseau et al. identified p.Asn540Lys in 8 of 16 familial cases (50.0%) and 13 of 13 sporadic cases (100.0%) [5]. Katsumata et al. reported p.Asn540Lys in 8 of 14 cases (57.1%) [6]. The proportions of p.Asn540Lys in HCH do not significantly differ between the previous and the present studies (chi-square test). The previous studies examined only the presence or absence of p.Asn540Lys. In contrast, this study identified other atypical variants than p.Asn540Lys. These atypical variants varied in terms of the position and substitution pattern of amino acid residue. This study did not find any significant differences in the radiological findings, age at diagnosis, or height SD score at diagnosis of patient groups between p.Asn540Lys and other variants. Further studies are warranted to delineate the relationship between genotype and phenotype among HCH.
Neurological sequela has been reported only for HCH [11,12], not for achondroplasia. Linnankiv et al. reported neurocognitive difficulties in 8 of 13 HCH patients with p.Asn540Lys (61.5%) and a possible relationship between the neurological sequela and temporal dysgenesis observed by brain MRI scan [13]. FGFR3 is expressed in the developing brain, but the mechanism underlying neurological sequela is not clarified yet. This study found intellectual disability or epilepsy in at least four or six patients with p.Asn540Lys, respectively. In contrast, no such sequela was reported in those with the atypical variants. The analysis with a small number of patients with atypical variants does not reach any conclusion. p.Asn540Lys might be a risk factor for neurological sequela, supporting the possible role of the genetic test for HCH in predicting neurological prognosis.
In this study, we determined pathogenic variants of FGFR3 in all cases of HCH. Thus, the combination of rhizomelic short stature and characteristic radiologic findings can reach the accurate diagnosis of HCH with the help of radiologic experts. The genetic test of FGFR3 is probably useful for atypical cases of suspected HCH such as relatively severe or mild cases resembling achondroplasia or idiopathic short stature, respectively. Furthermore, these results suggest that the genetic test is useful for assessing a potential risk of neurological sequela based on the presence of p.Asn540Lys.

Author Contributions

Conceptualization, T.I. and M.T.; resources, K.N., T.O., K.M., T.K. and F.T.; data curation, T.I., M.T. and G.N.; Formal analysis, T.I.; writing—original draft preparation, T.I.; writing—review and editing, M.T., K.N., T.O., K.M., T.K., F.T., G.N. and T.H.; supervision, G.N. and T.H.; funding acquisition, T.I. and T.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the grant entitled “A survey of contributing factors to therapeutic effect or adverse event of growth hormone” from the Foundation for Growth Science, Tokyo, Japan.

Institutional Review Board Statement

The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of Keio University School of Medicine (Protocol Code: 20170375 and date of approval March 30, 2018) and the Ethics Committee of Tokyo Metropolitan Children’s Medical Center (Protocol Code: H24-94).

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

Not applicable.

Acknowledgments

We appreciate the approval of this study and critical comments from the Foundation committee members of the Foundation for Growth Science (Susumu Yokoya, Akira Shimazu, Akira Matsuno, Yuko Hamasaki, Nobuyuki Murakami, Yoshikazu Nishi, Kunihiko Hanew, Reiko Horikawa, Toru Yorifuji, Yusuke Tanahashi, Junko Ito, Toshihiro Tajima, Koji Takano, Katsuyuki Matsui, Takahiro Mochizuki, Yutaka Takahashi, and Toshiaki Tanaka). We also thank Mizue Tsukui, Hiromichi Shoji, Yasuhiko Ikeda, Michiyo Matsuyama, Akiyoshi Nariai, Tomokazu Obi, Yasumichi Koide, Hiroshi Mochizuki, Mariko Ikeda, Mari Imamura, Yasushi Ito, Yuki Harada, Aya Shimada, Kazuhiro Shimura, Takeshi Munenaga, and Makoto Anzo for providing clinical information of their patients.

Conflicts of Interest

The authors declare no conflict of interest.

References

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Figure 1. Age and height SD score at diagnosis in probands with hypochondroplasia. Filled circles indicate those with p.Asn540Lys, and open circles show those with other variants.
Figure 1. Age and height SD score at diagnosis in probands with hypochondroplasia. Filled circles indicate those with p.Asn540Lys, and open circles show those with other variants.
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Table 1. Clinical and genetic characteristics of patients with hypochondroplasia.
Table 1. Clinical and genetic characteristics of patients with hypochondroplasia.
CaseFamilySexFGFR3 GenotypeAge at Diagnosis (Years)Height SDS at DiagnosisIntellectual DisabilityEpilepsyTemporal Lobe Dysgenesis
11Mc.1948A>C, p.Lys650Gln0NA
21Mc.1948A>C, p.Lys650Gln1NA
31Fc.1948A>C, p.Lys650Gln35−5.6
42Mc.970C>G, p.Leu324Val3−3.1NA
53Mc.1620C>A, p.Asn540Lys3−3.0NA
64Mc.1620C>A, p.Asn540Lys0NANANANA
75Fc.1620C>A, p.Asn540Lys3−3.7
85Fc.1620C>A, p.Asn540LysAdultNANA
96Mc.1052 C>G, p.Ser351Cys1−3.0NANANA
106Fc.1052 C>G, p.Ser351CysAdultNANANANA
117Fc.1620C>A, p.Asn540Lys5−2.2NANANA
128Mc.1949A>C, p.Lys650Thr6−2.9NANANA
139Mc.1620C>A, p.Asn540Lys2−2.4NANANA
1410Mc.1620C>A, p.Asn540LysNANA++
1511Fc.1620C>A, p.Asn540Lys5−2.9+NA
1612Fc.1620C>A, p.Asn540LysNANANA++
1713Fc.1620C>A, p.Asn540Lys5−5.1++
1814Fc.1620C>A, p.Asn540LysNANANANANA
1915Mc.1620C>A, p.Asn540Lys0NA+++
2016Mc.1620C>A, p.Asn540Lys1NANA
2117Fc.1620C>A, p.Asn540Lys2−3.2
2218Mc.1620C>A, p.Asn540LysNANANANANA
2319Fc.1950G>T, p.Lys650GlnNANANANANA
2420Fc.1620C>A, p.Asn540LysAdultNANANANA
2520Fc.1620C>A, p.Asn540Lys0.7−2.9+NA
2621Fc.1620C>A, p.Asn540LysNANANANANA
2722Mc.1620C>A, p.Asn540Lys0.3−0.6NA+NA
2823Mc.971T>A, p.Leu324His0.9−3.6NANANA
2924Fc.971T>A, p.Leu324His4−3.9NANANA
3025Mc.1620C>A, p.Asn540Lys1−3.3NANANA
3126Fc.1620C>A, p.Asn540Lys0−0.3NANANA
3227Fc.1620C>A, p.Asn540Lys3−3.5NANANA
3328Mc.1620C>A, p.Asn540Lys2−4.3NANANA
3429Fc.1620C>A, p.Asn540Lys2−3.4NANANA
3530Mc.1620C>A, p.Asn540Lys5−3.2NANANA
SDS, SD score; F, female; M, male; and NA, not available.
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MDPI and ACS Style

Ishii, T.; Takagi, M.; Nagasaki, K.; Ohara, T.; Miyai, K.; Kosho, T.; Takada, F.; Nishimura, G.; Hasegawa, T. Molecular Basis for Hypochondroplasia in Japan. Endocrines 2022, 3, 428-432. https://doi.org/10.3390/endocrines3030034

AMA Style

Ishii T, Takagi M, Nagasaki K, Ohara T, Miyai K, Kosho T, Takada F, Nishimura G, Hasegawa T. Molecular Basis for Hypochondroplasia in Japan. Endocrines. 2022; 3(3):428-432. https://doi.org/10.3390/endocrines3030034

Chicago/Turabian Style

Ishii, Tomohiro, Masaki Takagi, Keisuke Nagasaki, Toshio Ohara, Kentaro Miyai, Tomoki Kosho, Fumio Takada, Gen Nishimura, and Tomonobu Hasegawa. 2022. "Molecular Basis for Hypochondroplasia in Japan" Endocrines 3, no. 3: 428-432. https://doi.org/10.3390/endocrines3030034

APA Style

Ishii, T., Takagi, M., Nagasaki, K., Ohara, T., Miyai, K., Kosho, T., Takada, F., Nishimura, G., & Hasegawa, T. (2022). Molecular Basis for Hypochondroplasia in Japan. Endocrines, 3(3), 428-432. https://doi.org/10.3390/endocrines3030034

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