Evidence with neck webbing

Nuchal translucency (NT) refers to the fluid-filled space at the back of a fetus’s neck, visible during an ultrasound scan. Increased NT, due to a more significant fluid buildup, is referred to as nuchal edema, which is visible as swelling at the back of the fetus’s neck. Cystic hygroma is a significantly more severe form of increased nuchal translucency, often presenting as a multi-loculated fluid collection. ^{Reference Chervenak, Isaacson and Blakemore14,Reference Bekker, Haak, Rekoert-Hollander, Twisk and Van Vugt21,Reference Castelli, Todros, Mattutino, Torre and Panattoni50} Neck webbing (pterygium colli) is the result of excess skin folds in the neck area, which develop due to the resolution of a nuchal cystic hygroma formed in utero. Nuchal cystic hygroma occurs when there is an obstruction of the jugular lymphatic vessel, causing lymph to accumulate in the nuchal region’s lymphatic sacs. ^{Reference Chervenak, Isaacson and Blakemore14} The optimal window for nuchal translucency screening is between 11 and 14 weeks of gestation. ^{Reference Nicolaides47} Cardiovascular defects, such as bicuspid aortic valves and aortic coarctation, are common in individuals with Turner syndrome and other conditions involving neck webbing. About one-third of females with Turner syndrome have congenital heart defects. ^{Reference Richards and Garg8} Aside from genetic factors, it has been suggested that another proposed cause for these defects is lymphatic obstruction extending into the mediastinum. This can lead to significant fetal lymphedema that compresses the heart and major vessels, altering the blood flow and potentially causing defects like aortic coarctation, left ventricular hypoplasia and aortic valve anomalies . ^{Reference Loscalzo, Van and Ho9,Reference Chervenak, Isaacson and Blakemore14}

Putte (1977) explored the embryology of the lymphatic system to explain the link between webbed neck and congenital heart defects. Normally, jugular lymphatic sacs, which form lateral to the internal jugular vein, drain upper body lymphatic fluid into the venous system through the internal jugular vein. In Turner syndrome, these sacs fail to connect properly to the veins, causing lymph fluid to accumulate and the sacs to dilate. This elevated lymphatic pressure may also cause cardiac lymphatics to expand, potentially compressing the ascending aorta and altering intracardiac blood flow, which can lead to complex congenital heart defects. ^{Reference Putte48} Observations showed that lymphatic vessels converge at the heart’s base, with lymphatic ducts running alongside the aorta to the jugular lymphatic sac. ^{Reference Clark10} Clark (1984) suggested a similar theory where increased hydrostatic pressure in the obstructed jugular lymphatic sac might lead to the expansion of cardiac lymphatics at the base of the heart, compressing the developing ascending aorta and causing abnormalities in the left heart outflow tract. ^{Reference Clark10} Lacro (1988) further examined Clark’s theory in a study of 12 fetuses with Turner syndrome and nuchal cystic hygroma, aborted between 16- and 26-weeks’ gestation. In 9 of these fetuses, distended lymphatics were observed at the heart’s base, supporting the idea that increased pressure in the jugular lymphatic sac can extend to the cardiac lymphatics. ^{Reference Lacro, Jones and Benirschke16}

Studies on embryos with a 45X genotype and cystic hygroma, accompanied by dilated lymphatics around the heart and great vessels, have reported various left-sided congenital defects, such as hypoplastic left heart, aortic valve defects, aortic hypoplasia and coarctation. ^{Reference Lacro, Jones and Benirschke16,Reference Miyabara, Nakayama, Suzumori, Yonemitsu and Sugihara17} In a review of 193 patients with a 45X karyotype, Clark found that 30% of those with webbed necks had congenital heart defects, while 9% had normal hearts. ^{Reference Clark10} Coarctation of the aorta was observed in 25% of patients with neck webbing, but only in 3% of those with a normal neck. ^{Reference Stevenson and Hall49} In the study by Lacro et al. (1988), 75% of fetuses with cystic hygroma and hydrops fetalis had left-sided heart defects. ^{Reference Lacro, Jones and Benirschke16} While the characteristic features of Turner syndrome are often attributed to the abnormal 45X karyotype, in a prospective study conducted by Loscalzo et al. (2005) of 134 females with Turner syndrome, they found a strong association between central lymphedema (indicated by neck webbing) and both bicuspid aortic valve and aortic coarctation, regardless of karyotype. ^{Reference Loscalzo, Van and Ho9} The findings from Byrne et al. (1984) studies on female fetuses with cystic hygromas also suggest that nuchal cystic hygroma is a better indicator of cardiac abnormalities than the 45 X karyotype. ^{Reference Byrne, Blanc, Warburton and Wigger19} Berdahl et al. (1995) provided supporting evidence by analyzing data from the Iowa Birth Defects Registry, identifying 120 fetuses with webbed neck or excessive nuchal skin born between 1983 and 1988. Of these, 66% had blood flow defects. They also compared the incidence of congenital heart defects and flow-related abnormalities in patients with Down, Ullrich-Turner, and Noonan syndromes, with and without a webbed neck. The study found a higher incidence of flow-related defects in those with a webbed neck compared to those without. ^{Reference Berdahl, Wenstrom and Hanson15}

Research on fetuses with evidence of lymphatic abnormalities such as neck webbing indicates a strong link between abnormalities in the cardiac lymphatic system and congenital heart disease. Neck webbing, resulting from jugular lymphatic obstruction, is particularly associated with congenital heart defects, especially coarctation of the aorta. ^{Reference Clark10} These studies show a high prevalence of cardiac defects in individuals with neck webbing. Therefore, the presence of webbed neck or nuchal cystic hygroma on prenatal ultrasound or newborn examination should prompt thorough screening for congenital heart disease.

Evidence of a link with nuchal translucency

The nuchal translucency (NT) test is a common screening method used to identify fetuses at risk for chromosomal abnormalities such Down syndrome. This test uses ultrasound to measure the fluid at the back of the fetus’s neck, typically between 10 and 14 weeks of gestation. Bekker et al. (2005) suggested that an increase in the number of fetal jugular lymphatic sacs could be a cause of increased nuchal translucency, noting that 22 of 26 fetuses with increased nuchal translucency had a greater number of jugular lymphatic sacs, most likely due to a delay in the development of the lymphatic system. ^{Reference Bekker, Haak, Rekoert-Hollander, Twisk and Van Vugt21,Reference Castelli, Todros, Mattutino, Torre and Panattoni50}

Initially, heart defects in fetuses with increased NT were thought to result from chromosomal abnormalities. However, studies in euploid fetuses revealed that the incidence of cardiovascular defects increased with higher NT and that the degree of NT reflected the risk of congenital heart disease. ^{Reference Hyett, Moscoso, Papapanagiotou, Perdu and Nicolaides20,Reference Carvalho51} In a study by Hyett et al. (1996), 19 out of 21 cases of chromosomally normal fetuses with increased NT showed cardiac abnormalities, with aortic isthmus stenosis being the most common. ^{Reference Hyett, Moscoso, Papapanagiotou, Perdu and Nicolaides20} Carvalho (2005) suggested that nuchal translucency could serve as a predictor for heart defects, although it cannot be linked to a specify the type of cardiac abnormality. ^{Reference Carvalho51}

Nuchal edema and congenital heart defects both involve abnormal differentiation during embryogenesis. Our findings confirm a strong association between increased nuchal translucency (NT) in the first trimester and major cardiac defects in fetuses with normal karyotypes, with the risk of such defects rising as NT measurements increase. Given the significant relationship between NT and congenital heart disease, it can be used as a screening tool for congenital heart defects. According to Bansal (2013), one-third of fetuses with severe CHD can be identified through nuchal screening based on this association. ^{Reference Bansal5} Thus, echocardiography is recommended for all fetuses with increased NT, particularly those with measurements above the 99th percentile.

A potential genetic linkage

Recent advances in comparative molecular analysis have shown that vascular and lymphatic endothelial cells share a common lineage . ^{Reference Lampejo, Ghavimi, Hägerling, Agarwal and Murfee52,Reference Hong, Shin and Detmar53} This connection is supported by findings in lymphedema-distichiasis syndrome, an autosomal dominant disorder caused by a mutation in the FOXC2 gene and characterized by limb lymphedema, double rows of eyelashes, cardiac defects, cleft palate, extradural cysts and photophobia. ^{Reference Fang, Dagenais and Erickson13,Reference Brice, Mansour and Bell31,Reference Mellor, Tate and Stanton46,Reference Lampejo, Ghavimi, Hägerling, Agarwal and Murfee52} The FOXC2 gene is involved in the development of both the heart and the cardiac lymphatic system. ^{Reference Kume, Jiang, Topczewska and Hogan32,Reference Jiang, Tian, Nicolls and Rockson54} Mutations in FOXC2 result in normal-looking vessels with impaired lymphatic drainage due to abnormal valve development and defective mural cell coating in the collecting vessels. ^{Reference Petrova, Karpanen and Norrmén43} Therefore, haploinsufficiency of the FOXC2 gene can give rise to both cardiac defects and lymphatic abnormalities. ^{Reference Fang, Dagenais and Erickson13,Reference Brice, Mansour and Bell31}

In a systematic review by Burger et al. (2015), 15 genes were found to be essential for both cardiac and lymphatic vascular development in mouse embryos. Fourteen of these genes, when altered, resulted in both cardiac defects and NT. These genes primarily were involved in encoding components of the endothelium, emphasizing a link to endothelial differentiation, which is crucial for forming the heart, blood vessels and lymphatic vessels. ^{Reference Burger, Bekker, de Groot, Christoffels and Haak30} These findings suggest that alterations in genes critical to both lymphatic and cardiovascular development may explain the strong association between the two, with abnormal endothelial differentiation as the underlying pathophysiology.

The SOX18 transcription factor is another gene involved in both cardiovascular and cardiac lymphatic development . ^{Reference Irrthum, Devriendt and Chitayat12} SOX18 plays a crucial role in lymphangiogenesis ^{Reference Jones and Min1,Reference Csányi and Singla55} and cardiogenesis. ^{Reference Wegner56} In hypotrichosis–lymphedema–telangiectasia (HLT) syndrome, mutations in SOX18 lead to vascular, hair follicle and lymphatic defects. ^{Reference Irrthum, Devriendt and Chitayat12} Francois et al. (2008) found that mice with SOX18 mutations showed abnormalities in both the lymphatic and blood vascular systems. ^{Reference François, Caprini and Hosking42} Additionally, SOX18, along with SOX7 and SOX17 (collectively known as SOX F genes), are involved in the development of the heart, blood vessels, and lymphatic vessels, guiding endothelial cell differentiation during these processes. Mice with SOX17/SOX18 mutations exhibited deformities in anterior blood vessels, reduced endocardial cell differentiation, and abnormal endocardial fusion, which disrupts the formation of heart septa and valves, potentially giving rise to defects like atrioventricular septal defects. ^{Reference François, Caprini and Hosking42,Reference Francois, Koopman and Beltrame57} However, Sakamoto et al. (2007) did not find significant anomalies with SOX17/18 mutations, though weak SOX7 expression was linked to malformations in the anterior dorsal aorta and head/cervical vasculature, suggesting a regional effect. ^{Reference Sakamoto, Hara and Kanai-Azuma33} Despite these findings, the role of SOX17/18 in cardiac lymphatics and CHD remains uncertain and requires further research.

The PROX1 gene is essential for the development of both lymphatic vessels and the heart. It plays a key role in establishing and maintaining lymphatic endothelial cell identity by determining the specification of these cells from their precursors. ^{Reference Wigle and Oliver41,Reference Jiang, Tian, Nicolls and Rockson54} Deleting PROX1 can disrupt lymphatic development including cardiac lymphatics, as shown by Johnson et al. (2008), where PROX1 knockout mice developed blood-filled lymphatics and irregular lymphatic vasculature. ^{Reference Johnson, Dillard and Baluk44} Shakoor (2021) reported that PROX1 knockout mice had structural heart abnormalities, such as reduced heart size, hypoplastic ventricles, and a disorganized interventricular septum. Total PROX1 loss led to significant lymphatic defects in the aorta, myocardium, atrioventricular cushions and coronary arteries, resulting in a failure to separate blood and lymphatic vessels, which led to the development of postnatal chylothorax in some mice. ^{Reference Shakoor, Wu and Muley34} . According to Csányi (2019), PROX1 knockout mouse embryos did not survive beyond mid-gestation due to liver and lymphatic defects. ^{Reference Wigle and Oliver41} Additionally, a missense mutation in integrin alpha-9, whose expression is controlled by PROX1, was linked to severe chylothorax in human fetuses. ^{Reference Mishima, Watabe and Saito38,Reference Brouillard, Boon and Vikkula58}

The gene PODOPLANIN is also believed to play a role in the association between lymphatic system abnormalities and cardiovascular defects. Shakoor et al. (2021) found that PODOPLANIN-deficient mice had issues with separating blood and lymphatic vessels and some developed postnatal chylothorax. These knockout mice exhibited congenital lymphedema, impaired lymphatic transport and absent lymphatic capillaries. ^{Reference Shakoor, Wu and Muley34,Reference Schacht, Ramirez and Hong40} Thus, PODOPLANIN is crucial for differentiating lymphatic endothelial vasculature from embryonic. ^{Reference Breiteneder-Geleff, Soleiman and Kowalski39,Reference Vuorio, Tirronen and Ylä-Herttuala59}

Noonan syndrome is an autosomal dominant disorder marked by abnormal development in various parts of the body. Noonan syndrome occurs due to mutations in genes of the RAS-MAPK pathway, and the lymphatic defects in these syndromes have been demonstrated to have a genetic basis. ^{Reference Brouillard, Boon and Vikkula58} Joyce et al. (2016) found that all 11 patients with Noonan syndrome in their study had persistent lymphatic abnormalities, with nine patients having genital edema and eight patients having chylous reflux with lymphorrhea. The PTPN11 gene, which encodes SHP2, is commonly mutated in Noonan syndrome, appearing in 6 of the 11 patients studied. ^{Reference Joyce, Gordon and Brice35} PTPN11 mutation causes Noonan syndrome in about 50% of cases, with half of these patients also experiencing lymphedema. ^{Reference Smpokou, Tworog-Dube, Kucherlapati and Roberts45} Other mutations, such as a missense RIT1 variant, have also been associated with the syndrome. Kouz et al. (2016) noted that the phenotype associated with RIT1 mutations was particularly linked to a higher incidence of cardiovascular issues, such as hypertrophic cardiomyopathy and lymphatic complications. ^{Reference Kouz, Lissewski and Spranger36}

These studies suggest that mutations in shared genes may explain the possible association between lymphatic abnormalities and congenital heart defects. This supports the hypothesis of a shared molecular marker linking cardiac lymphatics and CHD. The genes discussed are highlighted in Table 2 and represent key candidates for future research into the underlying causes and potential treatments of CHD.