Vertebral Bone Density Abnormalities in Fetal Ultrasound: A Distinctive Clinical Sign of Spondylocarpotarsal Synostosis Syndrome MYH3‐Related

ABSTRACT

Background

Ultrasound diagnosis of fetal skeletal conditions remains challenging. MYH3 is a gene that encodes the embryonic myosin heavy chain; it is important for skeletal and muscular development and is strongly expressed during fetal development. Variants in MYH3 are involved in distal arthrogryposes 2A and 2B3 and in spondyocarpotarsal synostosis syndrome with contractures and pterygia, contractures of proximal and distal joints, variable spine anomalies and vertebral, carpal and tarsal fusions.

Key Findings

We describe a case in which prenatal ultrasonography detected abnormal bone density in the fetal spine. The fetus showed abnormal spinal segmentation, characterised by demineralisation and lacunar morphological tracts. x‐rays and histological examination confirmed the ultrasonographic findings. We describe a unique ultrasonographic phenotype of fetal spine that has not yet been described in the literature. This is likely associated with two MYH3 variants. Therefore, we believe that abnormal spinal segmentation should be considered a relevant ultrasound finding.

Discussion

Fetal ultrasound, together with radiological investigations, clinical examination of the fetal phenotype and histological investigations are essential in directing molecular genetic testing to identify rare diseases. We review the literature and describe a prenatal case with abnormal bone density in the spine. Whole‐exome sequencing (WES) analysis in the fetus was performed to explore variants compatible with ultrasound signs.

Summary.

• We believe that the ultrasound anomalies of the fetal spine we describe, could alert the clinician suspect a defective ossification as first sign of MYH3 related syndrome.

1. Introduction

Prenatal diagnosis of fetal skeletal conditions still remains a challenge, as detection of skeletal anomalies is possible by prenatal ultrasound, but an accurate and specific diagnosis is difficult. We describe the prenatal ultrasound features as well as phenotypic, radiological and histopathological characteristics of a fetus with spondylocarpotarsal syndrome and variants in the MYH3 gene. Starting from an increased nuchal translucency, we found that at 19 weeks of gestation the fetal spine showed an irregular aspect with alternating hyper‐ and hypoechogenic regions, suggestive of bone density abnormalities. Molecular analyses found two MYH3 variants.

The MYH3 gene (OMIM*160720) [1] is located at chromosome 17p13.1 and it is expressed in a variety of human fetal tissues: in the thymus, placenta, heart, liver, brain, as well as bone [2].

So far, over 60 variants of various types have been identified in MYH3‐associated diseases [3, 4, 5, 6]. In spondyocarpotarsal synostosis syndrome with contractures and pterygia, MYH3‐related (CPSFS1A and CPSFS1B), these are often respectively monoallelic or biallelic variants, in most cases loss of function [7, 8, 9, 10, 11, 12, 13], while missense variants in the MYH3 gene are most frequently associated with arthrogryposis 2A (OMIM#193700) and arthrogryposis 2B3 (OMIM#618436) [14]. In total, there are 38 individuals reported with CPSFS1A and 19 individuals with CPSFS1B [3, 5, 11, 14, 15, 16].

2. Case Report

A 38‐year‐old Egyptian woman was referred to our department for combined first trimester screening at 12 weeks of gestation. The husband was Caucasian and non‐consanguineous. Past maternal clinical and family history were unremarkable. Pregnancy was uneventful except for hypothyroidism treated with hormone replacement therapy. Conception was spontaneous and occurred after three previous pregnancies at term resulting in three male live births, one miscarriage at 7 weeks of gestation and before a healthy female.

Fetal ultrasound (Voluson E8, GE Medical System, Zipf, Austria) showed a crown‐rump length at the 5th percentile [17] with an increased nuchal translucency of 3.5 mm (> 99th percentile) [18]. Fetal anatomy was normal according to gestational age. Based on the increased risk for fetal aneuploidies, the couple consented to chorionic villus sampling, which revealed a 46,XX normal female karyotype. CGH‐Array analysis (Agilent CGH Microarray, 8x60K) identified a 1.10‐Mb deletion of maternal origin on chromosome 2: arr[GRCh37] 2q14.3(122863266_123973577). As it spans a region with no known coding genes and it has never been described in the literature or reported in disease (DECIPHER, ClinVar) [19, 20] or reference population (DGV) [21] databases, this copy number variant (CNV) was considered of uncertain significance.

At 19 weeks of gestation, second‐level ultrasound showed intrauterine growth restriction with fetal biometry and bone segmentation at the 5th and at the 3rd percentile for gestational age, respectively [22]. The fetal spine pointed out an irregular aspect with alternating hyper‐ and hypoechogenic regions, suggestive of bone density abnormalities rather than skeletal abnormalities (Figure 1). After further counselling, the woman proceeded to termination of pregnancy and a 297‐g fetus was delivered.

FIGURE 1.

Ultrasound images showing abnormal hypoechogenicity of the fetal spine. (a–c) Longitudinal planes showing the presence of alternating bright (white arrow with b) and hypoechogenic (white arrow with h) regions in the fetal spine, suggestive of bone density abnormalities and demineralisation. (d) 3D image of the fetal back showing the presence of bone structural abnormalities.

The x‐rays of the fetal skeleton showed absence of the D7 vertebral body and an abnormal spinal segmentation, characterised by demineralisation and lacunar morphological tracts (Figure 2a,b).

FIGURE 2.

x‐rays of the fetal skeleton and fetal autopsy examination after delivery. (a) Lateral and (b) front‐side images that reveal the absence of the seventh dorsal vertebra and an abnormal spinal segmentation characterised by demineralisation and lacunar sections. (c) The fetus showed a dysmorphic face with a broad forehead, mild hypertelorism, a long philtrum and low‐set ears. Lumbosacral scoliosis was rotated towards the right side of the body. The pelvis was also hypoplastic. (d) The lateral view of the face evidenced low‐set ears, a flat nasal profile, and micro‐retrognathia. (e) Histological section of the hemivertebra. The hypertrophic cartilage was irregularly oriented (arrows) and there were patchy areas of abnormal ossification (stars) (haematoxylin and eosin 4 HPF).

The fetal autopsy was performed according to international guidelines [23]. Tissue samples were fixed in 10% pH 7 buffered formalin. Fetal bones were kept in a weak decalcifier (fixative Gooding Stewart, Bio‐Optica, Milan, Italy) for 24–36 h, then dissected and processed. Histological slides were stained with standard haematoxylin and eosin. Growth restriction was confirmed (5th percentile) [24], and multiple dysmorphisms, such as broad forehead, mild hypertelorism, long philtrum, multiple bilateral pterygia, bilateral single transverse palmar crease, absence of foot creases, pulmonary hypoplasia and intestinal malrotation were noted (Figure 2c,d). Skeletal anomalies included right‐convex lumbosacral scoliosis and small pelvis. Histological examination displayed abnormal vertebral ossification and hypertrophic cartilage, confirming the ultrasound aspect of alternating hyper‐ and hypoechogenic regions (Figure 2e).

The hypotheses of spondylocarpotarsal synostosis syndrome (SCT) and spondylocarpotarsal synostosis syndrome with contractures and pterygia, MYH3‐related were formulated. Accordingly, whole‐exome sequencing (WES) analysis in the fetus was proposed to explore variants in the filamin B (FLNB) and myosin heavy chain 3 (MYH3) genes. Genomic DNA from the fetus was sequenced employing the Agilent All Exon V.6 kit (Agilent Technologies Inc., Santa Clara CA, USA) and HiSeq2500 Illumina sequencer (100‐bp paired end sequence). Alignment to the reference genome (GRCh37) was performed using the Burrows‐Wheeler Alignment (BWA) tool and Genome Analysis Toolkit (GATK). WES data of the fetus and read alignment analysis were checked for coverage depth and alignment quality employing the Bedtools software package. Sanger sequencing was performed on the DNA of the parents. No variants were found in the FLNB gene, while a de novo heterozygous missense variant c.590C>T, p.(Ala197Val) and a heterozygous nonsense variant of maternal origin c.5110G>T, p.(Glu1704*) were detected in the MYH3 gene (NM_002470.4) in the proband. Neither variant was present in reference population databases (gnomAD v4.0.0 and TOPMed Freeze 10, accessed on 2024.12.20) [25, 26]. The nonsense variant generates a premature stop codon likely leading to nonsense‐mediated decay of the transcript, or possibly to the synthesis of a severely truncated protein, which is compatible with the pathogenic mechanism for recessive MYH3‐related conditions [7]. The missense variant occurs at a conserved position within the myosin motor domain of the protein and was classified as deleterious by multiple in silico predictors (CADD, MutationTaster, MetaRNN) [27, 28, 29]. Either variant can be classified as likely pathogenic according to ACMG/AMP recommendations [30]. The phase of the two variants could not be determined.

3. Discussion

Herein we describe a fetus with bone density irregularities detected by ultrasound. The aspect of alternating hyperechoic and hypoechoic regions in the fetal spine is quite a unique finding.

The classification and the diagnosis of skeletal dysplasia itself have been hampered by the rarity of the condition and the various etiologies. Many skeletal conditions can be detected by an abnormally shortened femur length or by the presence of hand, foot abnormalities as well as deformities of the head and face. Sonographic assessment of the fetal spine may provide important information to lead on the type of skeletal dysplasia: unpaired and poorly formed vertebral centres resulting in a pebble‐like appearance are typically described in the Jarcho Levin syndrome [31]. Chondrodysplasia punctata can be suggested by the presence of calcifications in the coccyx and heel and mild stippling of the epiphysis due to premature calcification [32]. Hypophosphatasia includes a decreased echogenicity of the bones, with an undermineralisation of the skull and the spine [33].

In our case report we describe an abnormal spinal segmentation, characterised by demineralisation and lacunar morphological tracts, documented by x‐rays and histologically confirmed. The abnormal spinal segmentation should be considered a relevant ultrasound finding.

Molecular analysis found two variants in the MYH3 gene. As MYH3 is expressed in fetal bone and plays a role in morphogenesis, its loss may account for skeletal abnormalities [12]. MYH3‐related skeletal dysplasias, also called ‘contractures, pterygia and spondylocarpotarsal fusion syndrome’ (CPSFS1A, OMIM#178110 autosomal dominant and CPSFS1B, OMIM#618469 autosomal recessive), are characterised by contractures of proximal and distal joints, pterygia involving the neck, elbows, fingers and/or knees, and variable vertebral, carpal and tarsal fusions [34]. Inter‐ and intra‐familial variability has been observed [7]. Based on the MYH3‐associated phenotypes reported so far, we hypothesised that the two variants may be in trans, and either the de novo missense variant was sufficient to cause the observed clinical phenotype, or, more likely, the combination of the two variants was required to determine the phenotype in a recessive manner [7, 8, 9, 10, 11, 12, 13, 16]. However, the exact mode of inheritance of the condition remains undefined, because the phase of the variants could not be determined and the mother declined further analysis on the fetal tissues.

Only about 60 patients with MYH3 variants have been described in the literature. Prenatal diagnosis of fetal spinal anomalies associated with MYH3 variants is rare, probably due to the precocious lethal phenotype, which prevents a molecular diagnosis. We discuss afterwards the six published prenatal cases with variants in the MYH3 gene and spinal involvement [11, 15, 16, 35] (Table 1).

TABLE 1.

Prenatal, postnatal and molecular findings of our case and the six published prenatal cases with variants in the MYH3 gene and spine involvement.

Author	Carapito et al. [17]	Zhang et al. [19]	Kamien et al. [13]			Yang et al. [20]	Our case	Total
Consanguinity	−	−	−	+	+	−	−	2/7
Prenatal features
Time of first detection	10 WG	11+4 WG	1st trimester	1st trimester	12 WG	25 WG	12 WG
Increased nuchal translucency/cystic hygroma	+	+	+	+	+	+	+	7/7
Fetal biometry < 5th percentile	−	−	+	−	−	−	+	2/7
Pterigya	−	−	+	−	+	−	−	2/7
Flexion contractures	−	−	+	−	−	−	−	1/7
Clubfoot	−	−	+	−	−	−	−	1/7
Scoliosis and vertebral fusion	+	−	+	−	−	+	−	3/7
Alternating hypo/hyperechogenic regions in the spine	−	−	−	−	−	−	+	1/7
Fetal immobility/abnormal fetal movement	−	−	−	−	+	−	−	1/7
Genetic analyses
Karyotype	N (46,XX)	N	NA	N	NA	NA	N (46,XX)
CMA test	N	N	N	N	NA	N	arr[GRCh37] 2q14.3(122863266_123973577)x1 mat
WES/WGS analysis (MYH3 gene, NM_002470.4)	c.[4031 T>C];[=] p.[(Leu1344Pro)];[=]	c.[3044_3047delinsTCAATTTGTT];[=] p.[(Glu1015_Asp1016delinsValAsnLeuPhe)];[=]	c.[1259A>G];[4522 + 8A>C] p.[(Gln420Arg)];[(?)] a	c.[1376del];[1376del] p.[(Gly459Valfs*122)];[(Gly459Valfs*122)]	c.[4774C>T];[4774C>T] p.[(Gln1592*)];[(Gln1592*)]	c.[3872A>C];[=] p.[(Gln1291Pro)];[=]	c.[590C>T];[5110G>T] p.[(Ala197Val)];[(Glu1704*)]
ACMG/AMP variant class (and criteria)	4 (PM2, PP3, PP2, PP5)	4 (PM2, PM4, PP1, PP4)	I: 4 (PVS1, PM2, PP3) II: 4 (PVS1_S, PM2, PM3)	4 (PVS1, PM2)	4 (PVS1, PM2)	4 (PM2, PP3, PM6, PP2)	I: 4 (PS2, PM2, PP3, PP2) II: 4 (PSV1, PM2)
Autoptic/Postnatal features
Time of first examination	Birth	21+3 WG	21 WG	18 WG	25 WG	NA	21 WG
Vertebral fusions and scoliosis	+	−	+	+	+	NA	+	5/6
Short stature	+	−	+	−	−	NA	+	3/6
Multiple pterygia	+	−	+	+	+	NA	+	5/6
Muscular contractures	−	−	+	+	+	NA	−	3/6
Severe joint limitation	+	−	+	+	−	NA	−	3/6
Absent palmar creases	+	−	+	−	−	NA	+	3/6
Campodactyly	−	−	+	−	−	NA	−	1/6
Hypertelorism	−	−	+	+	−	NA	+	3/6
Posteriorly rotated ears	+	−	+	−	−	NA	−	2/6
Cleft palate	+	−	−	−	+	NA	−	2/6
Clubfoot, talipes equinovarus	−	−	+	−	−	NA	−	1/6
x‐rays findings
Fusion of vertebral bodies	+	NA	+	NA	NA	NA	−	2/3
Demineralisation and lacunar sections	−	NA	−	NA	NA	NA	+	1/3
Conclusion of pregnancy
	B	TOP	FD	FD	TOP	LF	TOP

Abbreviations: ACMG/AMP, American College of Medical Genetics and Genomics–Association for Molecular Pathology; B, born; CMA, chromosomal microarray analysis; FD, fetal death (< 24WG); LF, lost to follow‐up; N, normal; NA, data not available; S, stillbirth (≥ 24 WG); TOP, termination of pregnancy; WES, whole‐exome sequencing; WG, weeks of gestation; WGS, whole‐genome sequencing.

^a mRNA studies showed that both are splicing variants resulting in a nonsense‐mediated decay.

Carapito was the first to notice an increased nuchal translucency and abnormal spine in a fetus with a MYH3 variant [15]. Diffuse vertebral segmentation anomalies were confirmed after birth.

Zhang reported in 2020 a case of increased nuchal translucency associated with a MYH3 variant [16]. No specific skeletal fetal anomalies were evident. After the discovery of the familial variant, the couple opted for termination of pregnancy. Autopsy did not show skeletal anomalies or other abnormalities. Since the termination was at 21 weeks of gestation, we cannot exclude later manifestation usually associated with the MYH3 phenotype.

In 2022, Kamien described a lethal phenotype due to MYH3 variants in three families [11]. In the first family, first trimester screening detected a nuchal fold of 4.5 mm; at the time of amniocentesis, fetal biometry was < 5th percentile and the fetus showed micrognathia, mild scoliosis, and bilateral fixed flexion at the knees and wrists. The x‐rays at autopsy revealed fusion of the posterior elements of the vertebral bodies of the cervical and thoracic spine. In Family 2, the third and fourth pregnancies were marked by cystic hygroma and followed by fetal death and molecular analysis was performed only in the last pregnancy. In Family 3, the proband showed cystic hygroma and multiple pterygia. The post‐mortem examination also revealed scoliosis and vertebral fusion.

In 2023, Yang described two cases and only Case 2 showed a spinal involvement (irregularly placed thoracic vertebrae with scoliosis and partial vertebral fusion) and increased nuchal translucency [35].

In a recent publication, Qin in 2023 [36] analysed with WES 144 fetuses with structural anomalies: 25 of them showed musculoskeletal anomalies and in case 2949 with flexion contractures and clubfoot, a pathogenic variant of MYH3 was found. However, no anomalies in the spine are described.

To our knowledge, this is the first case of prenatal ultrasound evaluation of irregular fetal spine with alternating hyper‐ and hypoechogenic regions, associated with abnormal spinal segmentation characterised by demineralisation and lacunar morphological tracts at x‐rays post‐termination and confirmed by abnormal vertebral ossification and hypertrophic cartilage at the histological examination. The fact that an affected fetus could not show a severe phenotype like any other patients at the precocious gestational age may suggest that the manifestations might be aggravated dynamically during late pregnancy or perinatal period, as carpotarsal fusions or overlapping fingers [16]. So, we may speculate that the appearance of a different degree of spinal mineralisation could evolve during fetal development and the first detection of this feature should alert the clinician.

Patients with mono‐ or bi‐allelic variants in the MYH3 gene have contractures, mostly evident at birth. In one case out of seven, flexion contractures are reported also in the prenatal period [11]. All the prenatal reported cases showed increased nuchal translucency/cystic hygroma, a non‐specific feature found in different pathological conditions. Unlike previous findings, in our case, alternating hypo‐ and hyperechogenic regions were noticed in the spine, the possible first signal of this condition, which was confirmed in the autopsy with demineralisation and lacunar sections. In the radiological guidelines, defective ossification of vertebral bodies leads to a differential diagnosis between hypophosphatasia and achondrogenesis type 1A, 1B or 2 [37]. We can therefore state that defective ossification of vertebral bodies can also be considered a distinctive sign of spondyocarpotarsal synostosis syndrome MYH3‐related.

Our case is clinically impactful because it highlights the pivotal role that prenatal ultrasound plays in early detection and plausible expansion of the phenotypic spectrum of MYH3 variants, particularly those with early prenatal onset. To our knowledge, this is the first case in the literature where prenatal ultrasound features are reported together with the phenotypic, radiological and histopathological details of a fetus with spondylocarpotarsal syndrome and variants in the MYH3 gene and it can represent an example to guide the diagnostic suspicion. Fetal ultrasound, together with radiological investigations, clinical examination of the fetal phenotype and histological investigations, are of fundamental importance in directing molecular genetic testing to identify rare diseases.

Author Contributions

Immacolata Blasi: conceptualization (equal), resources (equal), writing – original draft (equal), writing – review and editing (equal). Marzia Pollazzon: conceptualization (equal), resources (equal), writing – original draft (equal), writing – review and editing (equal). Stefano Giuseppe Caraffi: investigation (equal), supervision (equal). Roberta Zuntini: investigation (equal), methodology (equal). Giuseppina Comitini: writing – review and editing (equal). Maria Paola Bonasoni: investigation (equal), methodology (equal). Jessica Daolio: data curation (equal). Sheila Unger: supervision (equal), validation (equal). Lorenzo Aguzzoli: supervision (equal). Andrea Superti‐Furga: supervision (equal), validation (equal), visualization (equal). Livia Garavelli: supervision (equal), validation (equal).

Consent

An appropriate informed consent to publish was signed by the parents.

Conflicts of Interest

The authors declare no conflicts of interest.

Blasi I., Pollazzon M., Caraffi S. G., et al., “Vertebral Bone Density Abnormalities in Fetal Ultrasound: A Distinctive Clinical Sign of Spondylocarpotarsal Synostosis Syndrome MYH3‐Related,” Australasian Journal of Ultrasound in Medicine 28, no. 3 (2025): e70015, 10.1002/ajum.70015.