Criteria for radiologic diagnosis of hypochondroplasia in neonates

Molecular Basis for Hypochondroplasia in Japan

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.

Novel Physique Index for the Screening of Skeletal Dysplasia at Birth

This study aimed to devise a novel physique index and investigate its accuracy in identifying newborns with skeletal dysplasia in comparison with head circumference (HC)/height (HT) ratio. The birth weight (W), HT, and HC at birth of 1500 newborns were retrospectively collected. The linear regression equations and coefficients of determination (R²) were determined. The formulated equation was corrected by the mean weight for gestational age at birth (Wcorr) as a novel physique index for screening skeletal dysplasia. The index accuracy was assessed using receiver operating characteristic (ROC) curves in 11 newborns by fetal ultrasound and compared with that of the HC/HT ratio. The R² values between W and HT, (HT)², and (HT) ³ were 0.978, 0.990, and 0.993, respectively. Those between W and HC, (HC)², and (HC)³ were 0.974, 0.984, and 0.988, respectively. W/Wcorr × (HC/HT)³ was used as a novel physique index. Seven newborns had skeletal dysplasia. Our novel physique index had a higher area under the curve (AUC), sensitivity, and specificity than the HC/HT ratio (AUC: 1.00 vs. 0.86, sensitivity: 1.00 vs. 0.86, and specificity: 1.00 vs. 0.75, respectively). Our novel physique index was more accurate than HC/HT ratio and has the potential to accurately identify newborns with skeletal dysplasia.

Revisiting Skeletal Dysplasias in the Newborn

With over 400 reported disorders, the skeletal dysplasias represent a myriad of molecularly-based skeletal abnormalities. Arising from errors in skeletal development, the clinical spectrum of disease evolves through an affected individual's life. The naming and grouping of these disorders are ever-changing, but the fundamentals of diagnosis remain the same and are accomplished through a combination of prenatal ultrasonography and postnatal physical examination, radiography, and genetic analysis. Although some disorders are lethal in the perinatal and neonatal periods, other disorders allow survival into infancy, childhood, and even adulthood with relatively normal lives. The foundation of management for an affected individual is multidisciplinary care. Medical advances have offered new insights into reducing common morbidities through pharmacologic means. This review summarizes the normal skeletal development and discusses the 3 most common skeletal dysplasias that can affect the newborn.

Earlier detection of hypochondroplasia: A large single-center UK case series and systematic review

Hypochondroplasia (HCH) is a rare autosomal dominant skeletal dysplasia condition caused by FGFR3 mutations leading to disproportionate short stature. Classically HCH presents in toddlers or school-age children, as limb-to-trunk disproportion and is often mild and easily overlooked during infancy. We report experiences from a single-center UK HCH-cohort of 31 patients, the rate of antenatal HCH detection in our cohort (13/31, 41.9%) and describe relevant case-data for this subset of 13 patients. Inclusion criteria were patients with confirmed molecular HCH diagnosis (by age 3 years) and presenting with short long-bones or large head size on antenatal ultrasound scan. We then conducted a systematic literature review using PUBMED and MEDLINE, analyzing patients with HCH and related antenatal findings. Antenatally suspected (with subsequent molecular confirmation) HCH has been reported 15 times in the literature (2004-2019). Key markers (consistent in both groups) included reduced; femur length, humeral length and increased; biparietal diameter and head circumference. HCH is increasingly detected both antenatally and in infancy, contrary to previous descriptions. This is likely due to greater HCH awareness, improved imaging, and easier molecular testing. Thus, one should consider HCH outside the classical presenting period. Studying the natural history of younger patients with HCH is important with the advent of several targeted FGFR3 therapies currently in trials for Achondroplasia, that may soon be trialed in HCH.

Identification of a novel mutation of FGFR3 gene in a large Chinese pedigree with hypochondroplasia by next-generation sequencing: A case report and brief literature review

RATIONALE

Hypochondroplasia (HCH) is the mildest form of chondrodysplasia characterized by disproportionate short stature, short extremities, and variable lumbar lordosis. It is caused by mutations in fibroblast growth factor receptor 3 (FGFR3) gene. Up to date, at least thirty mutations of FGFR3 gene have been found to be related to HCH. However, mutational screening of the FGFR3 gene is still far from completeness. Identification of more mutations is particularly important in diagnosis of HCH and will gain more insights into the molecular basis for the pathogenesis of HCH.

PATIENT CONCERNS

A large Chinese family consisting of 53 affected individuals with HCH phenotypes was examined.

DIAGNOSES

A novel missense mutation, c.1052C>T, in FGFR3 gene was identified in a large Chinese family with HCH. On the basis of this finding and clinical manifestations, the final diagnosis of HCH was made.

INTERVENTIONS

Next-generation sequencing (NGS) of DNA samples was performed to detect the mutation in the chondrodysplasia-related genes on the proband and her parents, which was confirmed by Sanger sequencing in the proband and most of other living affected family members.

OUTCOMES

A novel missense mutation, c.1052C>T, in the extracellular, ligand-binding domain of FGFR3 was identified in a large Chinese family with HCH. This heterozygous mutation results in substitution of serine for phenylalanine at amino acid 351 (p.S351F) and co-segregates with the phenotype in this family. Molecular docking analysis reveals that this unique FGFR3 mutation results in an enhancement of ligand-binding affinity between FGFR3 and its main ligand, fibroblast growth factor 9.

LESSONS

This novel mutation is the first mutation displaying an increase in ligand-binding affinity, therefore it may serve as a model to investigate ligand-dependent activity of FGF-FGFR complex. Our data also expanded the mutation spectrum of FGFR3 gene and facilitated clinic diagnosis and genetic counseling for this family with HCH.

A rare case of pelvic bone duplication

Iliac bone malformations are rare and result from early disturbance of the genetic and epigenetic processes that come together to form the pelvic girdle. We report the case of a 5-month-old boy found to have a duplication of the ilium and describe the likely causes of this very rare malformation.