Prenatal Diagnosis of a Heterotaxy Syndrome

A 35-year-old gravida 6, para 1 woman was referred to our fetal care center after a 12 6/7-week fetal sonogram in a dichorionic-diamniotic twin pregnancy revealed congenital anomalies. Previous to that ultrasonography, her pregnancy had been uncomplicated, but this early sonogram revealed the demise of 1 twin and a 2-vessel umbilical cord and a small omphalocele in the surviving twin. Subsequent imaging at 15 4/7 weeks' gestation noted additional abnormalities in the surviving twin, including a suspected complete atrioventricular canal (CAVC) defect, an abnormal cerebellum, and calcifications in the fetal abdomen. A repeated sonogram at 19 1/7 weeks' gestation also noted short long bones, echogenic kidneys, a sacrococcygeal extension, mild cerebral ventriculomegaly, and an absent cavum septum pellucidum in addition to the previously identified anomalies. The woman has a history of factor V Leiden and MTHFR variant, which were thought to contribute to her history of multiple miscarriages. Maternal karyotype was found to be normal (46, XX). Maternal medications included prenatal vitamins, methylfolate, and lovenox.Fetal magnetic resonance imaging (MRI), ultrasonography, and echocardiography were performed at 20 1/7 weeks' gestation. Imaging was notable for complex congenital heart disease consistent with double outlet right ventricle (DORV) with a CAVC defect, pulmonary hypoplasia, and partial anomalous pulmonary venous return (location of return unclear, but the images suggested a return to the central portion of the atrial mass), with the stomach on the right (Fig 1). This combination of features was consistent with heterotaxy syndrome.Additional anomalies identified included a small liver-containing omphalocele, a small posteriorly positioned fetal stomach with an echogenic and irregular internal surface, multiple abnormal calcifications in the fetal abdomen (Fig 2), sacrococcygeal extension, mild bilateral cerebral ventriculomegaly (10 mm on each side measured at the widest point of each lateral ventricle in the axial view), a widely spaced gap between the first and second toe on each foot, intermittent distention of the fetal hypopharynx, echogenic intracardiac focus, a 2-vessel umbilical cord, and overall small fetal measurements with long bones lagging behind gestational age by 2 to 3 weeks (Fig 3).Due to the clinical concern for heterotaxy syndrome, the family was consulted by a multidisciplinary team at our center including cardiology, general surgery, neurology, and genetics.The cardiology team reviewed that right atrial isomerism is a subset of heterotaxy syndrome and that DORV, CAVC defects, and anomalous pulmonary venous return are common findings with this type of heterotaxy. In this patient, DORV was associated with a small posterior pulmonary artery and a large anterior aorta with antegrade flow across the pulmonary valve into small branch pulmonary arteries, and the CAVC defect was observed to have good function. It was unclear based on imaging at 20 weeks' gestation whether 1 or 2 ventricles were present, and venous anatomy was ambiguous, although single-ventricle physiology was thought to be the more likely outcome. At 36 weeks' gestation, another fetal echocardiogram was performed, which revealed a left-dominant CAVC defect with severe right ventricular hypoplasia and DORV. Bilateral superior vena cava was also noted, which was consistent with isomerism. Antegrade pulmonary flow was still observed with a mildly small pulmonary valve but with normal-sized confluent branch pulmonary arteries. The cardiology team counseled the family that postnatal management would include transfer to the cardiac ICU soon after birth, with the timing of intervention dependent on other factors, such as the degree of pulmonary stenosis.Due to the omphalocele, general surgery was consulted. It was estimated that less than 5% of the total hepatic volume was within the small omphalocele, which also had a small aperture. The anticipated plan of treatment was to cover the omphalocele with a small xeroform dressing to protect it or reduce the liver and tie the umbilical cord at the skin level if the aperture was sufficiently large. Given the small nature of the omphalocele, the surgical team thought that a vaginal delivery was appropriate and that formal closure would not be needed in the newborn period.Neurologic consultation was undertaken to address the mild lateral cerebral ventriculomegaly. There was no observation of discrete parenchymal injury, hemorrhage, or cerebral malformation, suggesting that this could be a normal variant or subtle early manifestation of cerebral malformation. The inferior vermis appeared slightly blunted, which at 20 weeks' gestation could indicate inferior vermian hypoplasia or could normalize over the course of the pregnancy. The family was counseled that these features, especially in the setting of the other anomalies, were suggestive of an underlying genetic condition, and a repeated brain MRI was recommended at approximately 30 weeks' gestation to assess for interval brain growth and additional anomalies. A postnatal MRI was recommended when clinically stable and other conditions were assessed.Genetics was consulted to discuss the potential for an underlying genetic syndrome. Cell-free DNA screening for common aneuploidies had not been pursued due to the co-twin's death and challenges in differentiating the origin of the fetal DNA in the maternal circulation. Amniocentesis was performed at 16 1/7 weeks' gestation. Chromosomal microarray showed normal chromosomes (46,XY), without identification of a pathogenic variant. Infectious testing on amniotic fluid for cytomegalovirus via polymerase chain reaction was negative.Trio exome sequencing was then pursued to evaluate for potential monogenic conditions. A pathogenic hemizygous variant in ZIC3 (c.1060 + 1G>T) was identified in the fetal sample and noted to be maternally inherited. ZIC3 is associated with X-linked heterotaxy syndrome as well as X-linked VACTERL (vertebral anomalies, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, limb anomalies) association (Online Mendelian Inheritance in Man [OMIM 306955]: VACTERL association X-linked with or without hydrocephalus). The family was counseled about the 50% recurrence risk in a subsequent male fetus given that the variant is maternal in origin. The team reviewed screening and testing options for future pregnancies because there is also a 50% chance that a female fetus could carry this variant. The genetics team discussed that most female carriers do not have significant manifestations, but congenital heart defects have been reported in these individuals.The remainder of the pregnancy was monitored per the primary obstetrician without significant additional concerns.The male infant was born at 38 and 6/7 weeks' gestation via vaginal delivery with vacuum assistance. The infant was vigorous at birth, with Apgar scores of 8 and 8 at 1 and 5 minutes, respectively, and had a birthweight of 2,830 g (13th percentile), length of 18.5 in (47 cm) (9th percentile), and head circumference of 12.6 in (32 cm) (5th percentile). He required brief continuous positive airway pressure in the delivery room but transitioned to room air with normal oxygen saturations. His physical examination was notable for a 2/6 systolic murmur best heard at the left upper sternal border, a small omphalocele contained in the umbilical cord, and absence of sacral anomalies or dimples. He was brought to the cardiac ICU for further care.Abdominal ultrasonography on the newborn day was consistent with heterotaxy syndrome, including midline liver, right-sided stomach, asplenia, and left-sided inferior vena cava. No gallbladder was visualized. Echocardiography on the newborn day demonstrated a left-dominant CAVC defect, DORV, and multilevel subvalvular pulmonary stenosis. Head ultrasonography did not show any abnormalities.He remained in the cardiac ICU for the first week after birth and then transferred to the NICU for another week of care. He was hemodynamically stable and received daily furosemide. He remained in room air with goal oxygen saturation greater than 75% and was predominantly in the 80s. He was feeding ad lib by mouth and taking standard term formula and vitamin D supplementation. At 7 days of age, he had primary omphalocele closure with wedge resection of the liver; he tolerated the procedure well, and no complications were reported. His blood smear noted Howell-Jolly bodies were noted on blood smear, consistent with functional asplenia, for which he was started on prophylactic amoxicillin. Immunology was consulted with the plan for outpatient evaluation at 6 weeks after discharge.Despite a normal external-appearing sacral region, a spinal sonogram was performed at 13 days of age due to prenatal suspicion of sacrococcygeal extension, which revealed a low-lying position of the conus medullaris at the L3 level with a clumped appearance of the nerve roots, layering in a nondependent fashion with decreased pulsatility, concerning for tethered cord. Neurosurgery was consulted and recommended outpatient spinal MRI 3 months after discharge. Neurology also was consulted and recommended that brain MRI be obtained with spinal imaging.After his course in the NICU, he was then transferred to the cardiology floor. Due to poor weight gain, his feedings were increased to 24 kcal/oz. He passed his hearing screening and had normal results on the newborn screen. The infant was discharged at 18 days of age with a weight of 2,610 g and normal neurologic examination findings.At 2 months of age, the infant was readmitted to the hospital for symptoms of tachypnea, increased work of breathing, lethargy, and pale and mottled appearance. He was tachycardic, with heart rates in the 170s. This was diagnosed as decompensated heart failure with volume overload in the setting of pulmonary overcirculation and severe atrioventricular valve regurgitation. Chest radiography was performed, and a Morgagni-type diaphragmatic hernia was detected (Fig 4), with subsequent primary repair. He was started on bilevel positive airway pressure and milrinone, with captopril added 2 days after admission to facilitate weaning of milrinone. He was weaned to continuous positive airway pressure on hospital day 12 and then to room air the following day. At that time, propranolol was added to his regimen for rate control. The infant was discharged 31 days later with low-dose captopril and propranolol, with good cardiorespiratory status and improved function with medical management. He was unable to achieve full oral feedings and so was discharged with nasogastric feedings. He had follow-up appointments scheduled with cardiology, general surgery, and gastroenterology.At 6 months old, the infant underwent bilateral bidirectional Glenn connections and restriction of antegrade pulmonary blood flow by banding the main pulmonary artery. Fontan completion of single ventricle palliation will be considered closer to age 3 years. A nasal ciliary biopsy was also performed for evaluation of a primary ciliary dyskinesia, which was negative.By 11 months of age, the low-lying position of the conus medullaris normalized, when lumbosacral MRI noted normal termination of the conus at L2.At 2 years old, the child continues to be followed by cardiology and cardiac neurodevelopmental specialists. He is being observed for hypogammaglobinemia by immunology but has recovered from upper respiratory tract infections well and continues to take daily amoxicillin prophylaxis to manage a higher susceptibility to encapsulated bacteria due to his asplenia. He is also followed by a nutrition team because he experienced a lack of appetite after discharge until 2 years old, when the addition of cyproheptadine increased his appetite and growth. He has been evaluated by orthopedics due to ankle pronation, difficulty walking, and delayed motor milestones. Early intervention and physical therapy were pursued, and a supramalleolar orthosis was provided, (3) which helped him begin to walk. Fortunately, at his 2-year checkup, the patient has met all appropriate developmental milestones and is growing well (Fig 5).Heterotaxy is a rare condition in which incorrect left-right patterning during fetal development leads to abnormalities of the thoracoabdominal organs. Heterotaxy overall has an incidence of 1 in 5,000 to 1 in 7,000 live births. (1) Studies suggest that only approximately 20% of cases of heterotaxy will have an identified underlying genetic etiology. (1) Yi et al (1) identified a 1.4% rate of aneuploidy, a 2.8% rate of copy number variants, and a single gene etiology in 15.3% of cases. Autosomal recessive inheritance is the most common inheritance pattern observed in heterotaxy syndrome, but autosomal dominant and X-linked inheritance patterns are also observed. (2) ZIC3, located on Xq26, was the first gene known to be associated with heterotaxy syndrome and composes 3% to 5% of diagnosed cases. (3) More than 50 genes have been implicated in heterotaxy syndrome to date, revealing extensive locus heterogeneity. (3)(4) In addition to genetic heterogeneity, significant variability in phenotypic presentation exists due to the number of organs that undergo right-left differentiation during development.The combination of genetic and phenotypic heterogeneity makes it challenging to delineate a comprehensive categorization system. (5) Congenital heart defects are the most common structural anomaly associated with heterotaxy and have an incidence of approximately 1 in 125 live births. (1)(6) Basic classifications have been established in the categories of cardiac and extracardiac abnormalities, which are based on cardiac isomerism. (2) The first of 2 main classifications of heterotaxy is right isomerism, which entails asplenia, bilaterally bilobed lungs, and congenital heart defects and pulmonary artery anomalies. It is an observed abnormality in the left side patterning and a display of right-sided bilateralness. (3) The other classification is left isomerism, which often involves polysplenia, bilaterally trilobed lungs, congenital heart defects, and heart block. It is an observed abnormality in right side patterning and a display of left-sided bilateralness. (3) There is a significant overlap in cardiac phenotypic presentation between both classes of heterotaxy of the cardiovascular system, (7) but in general, there is greater severity in malformations seen in patients with right isomerism compared with left isomerism. (8) Both categories have significant rates of mortality from cardiovascular complications of approximately 10% in early childhood. (9) Life expectancy for patients with heterotaxy 1 year after diagnosis is greater than 85% for patients diagnosed as having asplenia and greater than 50% for patients diagnosed as having polysplenia.ZIC3 encodes a transcription factor in the ZIC family of the C2H2-type zinc finger proteins, which plays a role in the early development of the right and left axes. (10)(11) The zinc-binding region is highly conserved, and missense or nonsense mutations in the N-terminal can result in a loss of gene function. (12) ZIC3-related anomalies exist on a spectrum and can include isolated congenital heart disease but can also present as a syndrome with multiple affected organ systems. Some other associated anomalies include omphalocele, spinal anomalies, intrauterine growth restriction, and ventriculomegaly. (7) ZIC3 is the most common etiology of X-linked heterotaxy syndrome, and variants in ZIC3 have been reported in more than 75% of familial X-linked heterotaxy syndrome and approximately 1% of sporadic cases. (12) These changes can include nonsense and missense variants, insertions, and polyalanine repeat expansions. (3)(7) Variants in ZIC3 have also been associated with VACTERL association with or without the presence of hydrocephalus. (10) Eighty-six percent of males with a ZIC3 variant will present with heterotaxy and complex congenital heart defects, whereas most females are asymptomatic carriers. (7) Rarely, females can present with situs inversus and congenital heart disease likely due to skewed X inactivation. (7)To our knowledge, the variant identified in this patient has not been previously reported to be a pathogenic variant and is not present in ClinVar; however, the patient's clinical findings and genetic pattern suggest that this variant is associated with disease. The identified anomalies in this patient are consistent with the known ZIC3 phenotype. The variant is a canonical splice site variant expected to result in a null allele and loss of function, and the variant is also not present in gnomAD (Genome Aggregation Database).A unique finding in the patient we describe was the presence of a sacrococcygeal extension (also described as a vestigial tail). Human vestigial tails are dorsal protrusions from the lumbar, sacrococcygeal, or para-anal region and are extremely uncommon. (13) Human sacrococcygeal extensions can be classified as true tails or pseudotails. (14) True tails are covered by skin, contain muscle tissue, and have blood vessels and nerves, but no vertebrae or bony structures. They can be surgically removed if indicated. (13) A pseudotail is an overarching term for diverse types of lesions with the commonality of location in the lumbosacral region. (13) In a study examining fetal tail presence, 7 of 4,040 patients presented with sacrococcygeal extensions on fetal imaging. Two of those patients had a diagnosis of trisomy 13, and another fetus had Pfeiffer syndrome. (15) Outcomes are variable depending on the underlying genetic etiology and other associated anomalies. (15)There are no previous reports of patients with heterotaxy presenting with vestigial tails, and, to our knowledge, there is no known link between heterotaxy and the presence of a vestigial tail. However, variants in ZIC3 have also been identified in VACTERL association as well as heterotaxy syndrome, and sacrococcygeal extension or vestigial tail has been reported several times with the VATER/VACTERL association. (16)(17) Although both heterotaxy syndrome and VACTERL association can be composed of multiple congenital anomalies in multiple organ systems, the main overlap between the 2 is congenital heart defects. The most common congenital heart disease observed in VACTERL association is ventricular septal defects, (18) whereas DORV and atrioventricular canal defects are more commonly seen in heterotaxy syndrome. Moreover, it is known that all human embryos have a distinct tail during early fetal development, but it regresses and typically disappears at the end of the embryonic phase of development. We do note a similar delayed regression in this case where on fetal imaging there was a quite prominent sacrococcygeal extension, but at birth, the sacral region was grossly normal, and therefore no interventions were indicated. On a spinal sonogram at 13 days of age, the conus medullaris was low-lying at L3 with the suggestion of a tethered cord. By 11 months of age, when the lumbosacral MRI occurred, the conus medullaris was at L2 and there was no evidence of a tethered cord. Given this regression, it is possible that sacrococcygeal extension during fetal life is underdiagnosed because most affected fetuses do not have such detailed prenatal imaging.In summary, heterotaxy syndrome is a rare genetic developmental disorder in which visceral organs develop in atypical orientation throughout the body. Heterotaxy is clinically and genetically heterogeneous but is commonly associated with complex cardiovascular conditions along with anomalies in other organs that have laterality such as the lungs, spleen, and stomach. Evaluation should include comprehensive fetal imaging and broad genetic testing, such as exome sequencing, which should be included in parental counseling discussions in conjunction with genetic counseling for heterotaxy. Attention should be given to similar or overlapping conditions to guide screening and potentially provide anticipatory guidance for other concerns and considerations.