Prenatal ultrasonography and genetic analysis of fetal cleidocranial dysplasia: A case report

Abstract

BACKGROUND

Cleidocranial dysplasia (CCD) is an infrequent clinical condition with an autosomal dominant inheritance pattern. It is characterized by abnormal clavicles, patent sutures and fontanelles, supernumerary teeth, and short stature. Approximately 60%-70% of patients with CCD have mutations in the RUNX family transcription factor 2 gene. However, prenatal diagnosis of CCD is difficult when the family history is unknown.

CASE SUMMARY

We report a rare case of fetal CCD with an unknown family history, confirmed by prenatal ultrasonography and genetic testing at a gestational age of 16 weeks. The genetic reports indicated that the fetus carried pathogenic mutations in the RUNX family transcription factor 2 gene (c.674G>A). After careful consideration, the pregnant woman and her family decided to continue the pregnancy.

CONCLUSION

Definitive prenatal diagnosis of CCD should include family history, ultrasound diagnosis, and genetic analysis, especially if family history is unknown.

Key Words: Cleidocranial dysplasia; Genetic analysis; Ultrasonic diagnosis; Prenatal; Case report

Core Tip: Cleidocranial dysplasia is rare and hidden condition, and many cases are gradually diagnosed after birth. Features include multiple teeth, partial or complete absence of the clavicle, delayed closure of the sagittal suture and fontanel, which have an adverse effect on physical and mental health. We report a rare case of fetal cleidocranial dysplasia with an unknown family history at 16 weeks gestation, confirmed by prenatal ultrasonography and genetic testing. This case can inform future clinicians to aid in timely and correct diagnosis.

INTRODUCTION

Cleidocranial dysplasia (CCD) is a rare autosomal dominant systemic bone dysplasia with an incidence of about one in a million people[1]. The disorder is caused by mutations in the RUNX family transcription factor 2 (RUNX2) gene on chromosome 6p21. The RUNX2 gene is essential for differentiation of stem cells into osteoblasts. Therefore, mutations may cause defective bone formation. The disease can occur at any age, and about one-third of the patients have no family history. No significant difference is observed between the sexes. Due to the occult nature of CCD, severe bone growth and developmental abnormalities are gradually observed after birth. There is a need for a multifunctional approach to treat this disease, including tooth extraction and orthodontics, which can have psychological and physical consequences for patients. Therefore, it is important to recognize the disease early, especially in the fetal period. However, early recognition of fetal CCD is difficult when the family history is unknown. Here, we report a case of CCD diagnosed in a pregnant woman at 16 weeks gestation, with unknown family history. Based on a review of previous studies, we explored fetal ultrasonography diagnosis and genetic characteristics of CCD to improve the understanding of obstetricians and imaging physicians.

CASE PRESENTATION

Chief complaints

A 31-year-old woman (gravida 2, para 1), with normal intellectual development, was referred for ultrasound examination after 16 weeks of suspected hypomineralization of the skull bones and absence of the nasal bones.

History of present illness

A routine ultrasound examination was performed at the local hospital at 12 weeks of gestation. The nasal bone was not ossified, but the nuchal translucency thickness was normal. At 16 weeks of gestation, ultrasound examination in a local hospital revealed fetal bone dysplasia. Therefore, she came to our hospital for consultation.

History of past illness

The woman had a regular menstrual cycle, denied a history of exposure to drugs, radiation, and toxins in early pregnancy, and denied having a history of acute and chronic infection, heart disease, hypertension, diabetes, etc.

Personal and family history

The patient’s family history is unknown, but she self-reported that her first son was normal in appearance and intelligence, but her mother had unclear speech, low intelligence, and a small clavicle and skull.

Physical examination

The physical examination of this pregnant woman revealed short stature, large head and small face, sunken forehead, widening eye distance, low and flat nose, and overcrowding and malocclusion of supernumerary teeth. Besides, the shoulder joint range of motion was large, and the two shoulders could be closed in the chest.

Laboratory examinations

In this genetic test, the whole blood samples of fetal amniotic fluid and both parents of the proband were collected, and whole-exome sequencing was performed to detect the pathogenic genes.

Imaging examinations

The results of ultrasound examination in our hospital were: Biparietal diameter 3.6 cm, head circumference 13.2 cm, abdominal circumference 10.8 cm, and femur length 1.7 cm. Also, the fetal heart rate was about 145 beats/min. No nasal bone was shown, the cranial suture was widened, ossification of the skull and clavicle (more serious on the right side) was poor, echo decreased, and femur length was less than the 2.5^th percentile of corresponding gestational age. The scapula and ilium were also smaller, and no obvious abnormalities were observed in the placenta, amniotic fluid, umbilical cord and spine. The ultrasound measurements were equivalent to 16 weeks and 3 days of gestation. Two-dimensional (2D) and 3D ultrasonography of the fetus revealed suspected CCD features, including poor ossification of the skull, large fontanelle, and absence of nasal bones. Furthermore, the clavicle was short and straight, without a typical “S” shape (Figure 1).

Figure 1 Two-dimensional and three-dimensional ultrasound of fetal cleidocranial dysplasia. A: Three-dimensional (3D) ultrasonography showed enlargement of the anterior fontanelle (thick arrow); B: 3D ultrasound showed temporal suture widening (thin arrow); C: 2D ultrasound showed the absence of nasal bone (short arrowhead); D: 2D ultrasound showed that the clavicle was short and straight without a typical “S” shape (long arrowhead).

FINAL DIAGNOSIS

The woman received prenatal counseling due to the suspected CCD on prenatal ultrasound. If a pregnant woman has CCD, the risk of giving birth to a child with CCD per pregnancy is 50%, regardless of the sex of the fetus. Even if similar mutations are found, the severity of the CCD phenotype cannot be predicted. Therefore, fetal amniotic fluid and blood samples from parents were collected for genetic testing. Whole-exome sequencing technology was used to detect the variation related to fetal ultrasound phenotype, RUNX2 gene c.674G>A mutation, which was verified by Sanger sequencing. The results were consistent with the whole exon sequencing results (Figure 2). In addition, it was found that the mother was heterozygous, and the father was wild type. It was suggested that the fetus had clavicular/metaphyseal and maxillary dysplasia with or without short finger (toe) deformity. As the woman was diagnosed with CCD, the whole blood samples of the woman’s first son and her mother were collected for the genetic verification of single-gene genetic disease. It was found that the mother was heterozygous, and her son did not have this mutation (Figure 3).

Figure 2 Sequencing results show that the fetus carried pathogenic mutations in the RUNX2 gene (c.674G>A) (black arrow).

Figure 3 Pedigree of the affected family. Circles and squares represent females and males, respectively. Affected individuals are shown in black. Diamond represents current pregnancy. Slash represents death.

TREATMENT

The obstetrician fully interpreted the ultrasound and genetic test and reported the results to the pregnant woman. They informed the patient about the delivery management measures of CCD and the possible disease characteristics after birth, and respected the woman’s reproductive choice.

OUTCOME AND FOLLOW-UP

After careful consideration by the pregnant woman and her family, she chose to continue the pregnancy until delivery. A male neonate was delivered by cesarean section at 38 + 2 weeks of gestation, with a birth weight of 3250 g, length of 48 cm, and Apgar scores of 9 and 10 at 1 and 5 minutes, respectively. The neonate was discharged home 4 days after delivery, without complications. At 2 years and 7 months follow-up, the boy had well-aligned baby teeth, incomplete closure of the fontanel, short collarbone, and normal intelligence. We will continue to follow up.

DISCUSSION

CCD triad includes multiple teeth, partial or complete absence of the clavicle, and delayed closure of the sagittal suture and fontanelle[2,3]. CCD can be categorized into three types according to the genetic relationship and different affected bones: (1) Type I is the standard type, with familial inheritance and incomplete ossification of the skull and clavicle; (2) Type II is familial, with familial inheritance, but the skull is not involved; and (3) Type III is sporadic, with no familial inheritance, and the skull and clavicle are involved. This patient had a family history and belonged to type I. As the woman did not know she had CCD, this indicated CCD was insidious, but its heritability became high once it occurred.

Approximately 60%-70% of patients with CCD have a loss of function or haploidy insufficiency mutation of the RUNX2 gene, which is located on chromosome 6p21 and is an important transcription factor in chondrocyte maturation, osteoblast differentiation, and bone formation[4,5]. RUNX2 regulates mesenchymal cell proliferation in sutures and suture closure by inducing the signaling pathways of fibroblast growth factor, parathyroid hormone-like hormone, hedgehog and Wnt genes[6]. At present, fetal CCD with prenatal ultrasound and genetic analysis is rarely reported. Our review of studies published in English revealed only eight cases of fetal CCD diagnosed with prenatal ultrasound, including the present case (Table 1). There are some similarities between this and previous CCD cases, such as poor mineralization of skull and clavicle, and missing nose bone, but the biggest difference is that the family history of this case was unknown, which aggravated the difficulty of diagnosis. Therefore, it is important to carefully ascertain the medical history, family history, and even observe the physical characteristics of the pregnant woman. Finally, we continue with a comprehensive ultrasound and retrospective history, as well as genetic testing to confirm the diagnosis of the disease. CCD mainly affects bones formed by intramembranous ossification, such as the skull and clavicles. Its main characteristics are: (1) Short stature; (2) Hypoplasia of the clavicle, resulting in hypermobility of the shoulder, which can usually be approached forward; (3) Skeletal abnormalities such as conical chest with short ribs, flat feet, genu valgus (genu varus deformity), and scoliosis; (4) Hand abnormalities, such as short fingers and distal phalanges; and (5) Repeated upper respiratory tract and ear infections, hearing loss, early infant respiratory distress, and even language disorders and seizures. The child is in good general health with normal intellectual development[1,7-10]. Although the biological characteristics of the fetus and pregnant woman were consistent with the aforementioned description, the mental health issues of the woman’s mother needed exploration using a large sample.

Table 1 Literature review of fetal cleidocranial dysplasia diagnosed by ultrasound.

Ref.	Family history	Maternal history	Previous pregnancy	Gestational week at detection	Prenatal ultrasound findings	Genetic diagnosis
Hassan et al[9], 1997	Unknown	G2P1	Healthy female	19 weeks	Abnormal skull ossification; short femora; short humeri	No chromosome rearrangement of chromosome 6
Stewart et al[15], 2000	Positive	G3P2	CCD male, healthy female	14 weeks + 4 days	The hypoplastic clavicles and the cranium appeared less well ossified than expected for gestational age	Undetected
Paladini et al[11], 2000	NA	NA	NA	37 weeks	Late-onset skeletal dysplasia; clear frontoparietal bossing; hypomineralization of the cranial bones; the low nasal bridge; clavicular hypoplasia	Refused genetic testing
Winer et al[3], 2003	Negative	NA	NA	24 weeks	Clavicular hypoplasia; no ossification of the cranial parietal bone; very poor ossification of the frontal and pubic bones; the long bones growth restriction	An apparently de novo balanced t(2q;6q)(q36;q16) translocation
Soto et al[13], 2006	Positive	G3P1	Open anterior fontanelle at 5-year-old	18 weeks + 3 days	18 weeks + 3 days: Absence of nasal bone, the widened fontanelles; hypomineralized occipital bones; 21 weeks + 3 days: Intrauterine clavicle fracture	No RUNX2 gene mutation
Hove et al[14], 2008	Positive	G2P1	CCD child	13 weeks + 6 days	Severely delayed ossification of the vertebral spine; barely visible clavicles; poorly ossified calvarial bones	NA
Hermann et al[12], 2009	Positive	NA	NA	15 weeks + 4 days	Large fontanelles; lack of nasal bones; clavicles without the typical “S” form; severe delay in calvarial ossification	NA
Present case	Unknown	G2P1	Healthy male	16 weeks	Lack of nasal bones; large fontanelles; widened cranial suture; the poor ossification of skull and clavicle; short femur	Pathogenic mutations in the RUNX2 gene (c.674G>A)

G: Gestation; P: Production; CCD: Cleidocranial dysplasia; NA: Not available; RUNX2: RUNX family transcription factor 2.

The correct diagnosis of CCD involves clinical history, symptoms, signs, imaging findings, and genetic analysis. The main problem in CCD management is early diagnosis. Previous case reports on prenatal ultrasound diagnosis of CCD were based on abnormalities of the clavicle (hypoplasia and hypocalcification) and malcalcification of the skull (large fontanelle and wide cranial suture)[11]. Some researchers found that almost all fetuses with CCD had missing nasal bones, which was consistent with the finding of this study[12,13]. Ultrasonography has found early suggestive features of CCD as early as 14 weeks of gestation, such as severely delayed spinal ossification, clavicular hypoplasia, and skull ossification below gestational age. However, few studies have reported the prospective diagnosis of CCD in patients with a negative family history[14,15]. In addition, the ultrasonic diagnostic criteria of fetal fontanel and cranial suture width should be further studied to avoid missed diagnosis due to subjective factors. Natural delivery may cause potential damage to the fetal brain due to the delayed nature of CCD skull ossification, and a planned cesarean section is recommended in these cases. Therefore, the prenatal identification of CCD is of clinical importance.

Ultrasound may be the only prenatal diagnostic technique that can detect CCD when family history is negative and DNA testing is not available during pregnancy. 3D ultrasound is a better alternative compared with 2D ultrasound when the craniofacial disease is suspected. The ultrasound findings of clavicular hypoplasia are an important marker of CCD in high-risk families. However, clavicular hypoplasia is also seen in other disorders, including skeletal dysplasia syndrome and chromosomal abnormalities. For example, osteogenesis imperfecta congenita, an autosomal dominant genetic disorder, has prenatal ultrasound findings that include generalized hypomineralization of the long bones and calvarium, multiple bone fractures and severe shortening and bowing of the long bones. Although nasal bone deletions are most common in chromosomal disorders (e.g., trisomy 21 and 18), fetuses with trisomy 21 often have a thickening of the nuchal pellucidum, nasal bone dysplasia, abnormal venous blood flow, heart defects, and excessive amniotic fluid. Other bones should be carefully examined in fetuses with nasal bone deletions but normal karyotypes.

CONCLUSION

The prenatal diagnosis of CCD requires confirmation by ultrasound and genetic testing. Other bones should be carefully examined, especially for fetuses with nasal bone loss of unknown family history. 3D ultrasonography is more likely than 2D ultrasonography to show an enlarged fontanelle and a low mineralized skull. Understanding the family history, clinical features, ultrasound findings, and genetic characteristics of CCD can help in the early diagnosis of fetal CCD so that clinicians can decide on an appropriate delivery mode and postnatal bone monitoring so as to improve function, prognosis, and aesthetics.

ACKNOWLEDGEMENTS

We thank the patients for consenting us to share the details. We also appreciate the support of the hospital and the ultrasound department.