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.

Criteria for radiologic diagnosis of hypochondroplasia in neonates

BACKGROUND

A radiologic diagnosis of hypochondroplasia is hampered by the absence of age-dependent radiologic criteria, particularly in the neonatal period.

OBJECTIVE

To establish radiologic criteria and scoring system for identifying neonates with fibroblast growth factor receptor 3 (FGFR3)-associated hypochondroplasia.

MATERIALS AND METHODS

This retrospective study included 7 hypochondroplastic neonates and 30 controls. All subjects underwent radiologic examination within 28 days after birth. We evaluated parameters reflecting the presence of (1) short ilia, (2) squared ilia, (3) short greater sciatic notch, (4) horizontal acetabula, (5) short femora, (6) broad femora, (7) metaphyseal flaring, (8) lumbosacral interpedicular distance narrowing and (9) ovoid radiolucency of the proximal femora.

RESULTS

Only parameters 1, 3, 4, 5 and 6 were statistically different between the two groups. Parameters 3, 5 and 6 did not overlap between the groups, while parameters 1 and 4 did. Based on these results, we propose a scoring system for hypochondroplasia. Two major criteria (parameters 3 and 6) were assigned scores of 2, whereas 4 minor criteria (parameters 1, 4, 5 and 9) were assigned scores of 1. All neonates with hypochondroplasia in our material scored ≥6.

CONCLUSION

Our set of diagnostic radiologic criteria might be useful for early identification of hypochondroplastic neonates.

Prenatal ultrasound and MRI findings of temporal and occipital lobe dysplasia in a twin with achondroplasia

Thanatophoric dysplasia, hypochondroplasia and achondroplasia are all caused by FGFR3 (fibroblast growth factor receptor 3) mutations. Neuropathological findings of temporal lobe dysplasia are found in thanatophoric dysplasia, and temporal and occipital lobe abnormalities have been described recently in brain imaging studies of children with hypochondroplasia. We describe twins discordant for achondroplasia, in one of whom the prenatal diagnosis was based on ultrasound and fetal MRI documentation of temporal and occipital lobe abnormalities characteristic of hypochondroplasia, in addition to the finding of short long bones. Despite the intracranial findings suggestive of hypochondroplasia, achondroplasia was confirmed following postnatal clinical and genetic testing. These intracranial abnormalities have not been previously described in a fetus with achondroplasia.

Prenatal diagnosis of hypochondroplasia: Report of two cases

Hypochondroplasia (HCH) is an autosomal dominant skeletal dysplasia characterized by short extremities, short stature and lumbar lordosis, usually exhibiting a phenotype similar to but milder than achondroplasia (ACH). Mutations in the fibroblast growth factor receptor 3 (FGFR3) gene are present in a significant proportion of HCH patients. Reports of prenatal diagnosis of HCH are very rare and the phenotype/genotype correlation in these patients is poor. Here we present two sporadic cases with second trimester ultrasound findings consistent with a diagnosis of a non-lethal skeletal dysplasia. Ultrasound evaluation after 23 weeks of gestation showed a decreased rate of development of the femora (femur length <fifth centile), while biparietal diameter, abdominal circumference, and foot length were within normal limits. Femur length/foot and femur length/abdominal circumference ratios were <0.87 and <0.18, respectively. Prenatal cytogenetic and molecular genetic analysis was performed. Karyotype was normal and FGFR3 G380R mutation characteristic of ACH was excluded in both fetuses. Molecular genetic analysis carried out retrospectively revealed that both fetuses were heterozygous for the C1620A mutation resulting in N540K substitution in FGFR3, the most common mutation in HCH. We conclude that the combination of ultrasound and molecular genetic approach is helpful for establishing an accurate diagnosis of HCH in utero and subsequently for appropriate genetic counseling and perinatal management.

Prenatal Diagnosis of Hypochondroplasia: Three-Dimensional Multislice Computed Tomography Findings and Molecular Analysis

We report the first case of sporadic hypochondroplasia diagnosed in utero by computed tomography (CT) three-dimensional (3D) imaging and molecular analysis at 38 weeks' gestation. Prenatal sonographic examinations performed at 32 and 35 weeks' gestation revealed a rhizomelic shortness of the long bones (femur and humerus) with macrocephaly. Based on these findings, a nonlethal form of skeletal dysplasia was suspected and a multislice CT imaging with 3D reconstruction was performed depicting skeletal abnormalities which suggested hypochondroplasia. The prenatal diagnosis was confirmed by DNA mutation analysis of the fibroblast growth receptor 3 gene.

Radiographic and genetic diagnosis of sporadic hypochondroplasia early in the neonatal period

Hypochondroplasia is an autosomal dominant skeletal dysplasia expressing postnatal onset of short stature with mild rhizomelic shortening of the limbs. This manifestation leads to restricted prenatal diagnosis of the disorder. We report here on a sporadic case of a hypochondroplastic baby, whose prenatal sonographic measurements were serially recorded from 19 weeks of gestation. Mild shortening of the limbs became manifest after 26 weeks of gestation. Biparietal diameter was within the normal range throughout gestation. Both parents were of average stature. A tentative diagnosis of a nonlethal short-limb skeletal dysplasia was made. At birth, the clinical manifestations of the neonate were not characteristic, but the radiographic features raised the possibility of hypochondroplasia. Molecular analyses revealed a C to G mutation at nucleotide 1659 of the fibroblast growth factor receptor 3 (FGFR3) gene, a common mutation in hypochondroplasia.

Diagnosis of skeletal dysplasia by multidisciplinary assessment: a report of two cases of thanatophoric dysplasia

Skeletal dysplasias, a heterogeneous group of bone growth disorders, can be detected by routine prenatal ultrasound examination. As it is difficult to make a specific diagnosis, prediction of prognosis is of importance for obstetric management. In order to specify diagnosis, radiological, pathological and molecular genetic examination are often required. Our report describes two cases of thanatophoric dysplasia with different fetal sonographic findings. The classical classification of type I and II seems to be ambiguous as, in both cases, the same mutation in the fibroblast growth factor receptor 3 gene was found. The importance of comprehensive multidisciplinary assessment is emphasized.