Severe Form of Brachydactyly Type A1 in a Child with a c.298G > A Mutation in IHH Gene

Hypothesis: Symbrachydactyly

The term symbrachydactyly has been used for the phenotype of two or three short fingers or toes, hypoplasia of the middle and distal phalanges and variable syndactyly of the affected digits. Some clinicians have extended this diagnosis to include other phenotypes, specifically cleft hand, terminal transverse limb defects, hypoplasia of the thumb and fifth finger with nubbins for fingers 2, 3, and 4 and the hand deformity of the Poland anomaly. A malformations surveillance program can identify enough affected infants to characterize a phenotype. In the Active Malformations Surveillance Program in Boston (1972-2012) among 289,365 births, all infants and fetuses with structural abnormalities were identified from reading the examination findings by the pediatricians and pathologists and the results of diagnostic tests. Liveborn and stillborn infants were included, as well as fetuses from elective terminations because of anomalies identified in prenatal testing. We present the findings in 14 infants, all liveborn, who had symbrachydactyly of one or both hands (n = 12) or feet (n = 2). We suggest restricting the term symbrachydactyly to this single phenotype to improve counseling and to focus future research on identifying the cause(s).

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.

Application of two-dimensional and three-dimensional ultrasound in prenatal screening for brachydactyly deformity

This study aims to summarize the characteristics of prenatal ultrasonography of the fetus with brachydactyly. From November 2015 to December 2016, a total of 10,866 pregnant women underwent prenatal ultrasound screening at the gestational age of 17-26 weeks. Targeted ultrasonographic imaging of the fetal hands was performed. The multi-view observation of fetal fingers by ultrasound was performed at different flexions of fingers (stretching, bending and fist) to observe the ultrasonographic manifestations of metacarpals and phalanges, and the number, size, shape and arrangement of the ossification centers of metacarpals and phalanges. A comparation was performed on the prenatal sonographic findings and the results of follow-up after termination of pregnancy or birth. The prenatal ultrasound detected six cases of brachydactyly. Among these cases, five cases were bilateral and one case was unilateral. In these cases, more than one ossification center of phalanxes were invisible or significantly smaller. Furthermore, among the six cases of brachydactyly, the women of four cases chose to terminate the pregnancy, while the women of the other two cases had no other abnormalities and gave birth. In the two cases with multiple malformations, one case was complicated with osteodysplasty, cleft lip and palate, and pleural effusion, while the other case was complicated with limb body wall complex and malformation of the heart. Overall, our results suggest that the targeted two- and three-dimensional ultrasound imaging of the fetal hands in the second trimester of pregnancy can improve the detection of severe brachydactyly.

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.

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.