Lymphedema Panel

The lymphatic system is a subset of the circulatory system with vessels and nodes that transport lymph throughout the body and includes the tonsils, adenoids, spleen, and thymus. Lymph is a clear-to-white interstitial fluid comprised primarily of white blood cells, proteins, and lipids. The primary functions of the lymphatic system include ridding the body of infection and maintaining fluid balance. Improper lymphatic function can lead to lymph accumulation and swelling known as lymphedema. The prevalence of lymphedema is approximately 1.3 - 1.4 per 1000 people (Rockson et al. 2008. PubMed ID: 18519968). Lymphedema can result in infections and other complications including a form of lymphatic cancer called lymphangiosarcoma. Primary lymphedema is caused by pathologic development of the lymphatic system. Secondary lymphedema can arise from other conditions or treatments; most commonly from cancer and cancer treatments including lymphadenectomy (Gordon and Mortimer. 2007; Warren et al. 2007. PubMed ID: 17901744).

Hereditary lymphedema is clinically and genetically heterogeneous. Pathogenic variants in the following genes represent some of the more frequent causes of hereditary lymphedema.

FLT4 – Milroy Disease (MD; also known as Lymphedema Type I) is an autosomal dominant form of primary lymphedema with reduced penetrance. MD is characterized by lymphedema of the lower limbs (Brice et al. 2005. PubMed ID: 15689446). The swelling is often present at birth or develops in early infancy. Other common features include hydrocele in males, cellulitis, prominent veins, upslanting toenails, and papillomas.

FAT4 – Hennekam lymphangiectasia-lymphedema syndrome 2 (HKLLS) is an autosomal recessive form of primary lymphedema of the limbs and lymphangiectasia affecting the gut, pericardium, lungs, kidneys, and genitalia (Alders et al. 2014. PubMed ID: 24913602). Pathogenic variants in FAT4 are also associated with autosomal recessive Van Maldergem syndrome 2 (VMLDS2) which has many overlapping features with HKLLS, including distinct facial features such as flat face and nasal bridge, hypertelorism, epicanthus, small ears and mouth, and abnormal teeth (Alders et al. 2014. PubMed ID: 24913602). FAT4 pathogenic variants were found in 20% of patients with Hennekam lymphangiectasia; pathogenic variants in CCBE1 are also associated with Hennekam lymphangiectasia (Alders et al. 2014. PubMed ID: 24913602)

CCBE1 – Hennekam Syndrome is an autosomal recessive form of primary lymphedema characterized by severe lymphedema in the limbs, genitalia and face and complicated by facial dysmorphism and mental retardation (Hennekam et al. 1989. PubMed ID: 2624276). Facial features vary, but are typically characterized by a flattened face and nasal bridge, hypertelorism, epicanthal folds, small mouth, tooth anomalies, and ear defects accompanied by hearing loss. Lymphedema is progressive, often beginning in utero with hydrops fetalis, and can be asymmetrical (Van Balkom et al. 2002. PubMed ID: 12376947). Edema is typically accompanied by hypoproteinemia and immunologic abnormalities such as hypogammaglobulinemia and lymphocytopenia. Angiectasis of lymph vessels in the intestines and other organs (pleura pericardium, thyroid, and kidneys) are a hallmark of Hennekam Syndrome (Hennekam et al. 1989. PubMed ID: 2624276; Alders et al. 2009. PubMed ID: 19935664). Additional features may include congenital heart defects, pyloric stenosis, glaucoma, hypothyroidism, camptodactyly, rectal prolapse and renal anomalies (Angle and Hersh. 1997. PubMed ID: 9217224; Van Balkom et al. 2002. PubMed ID: 12376947; Al-Gazali et al. 2003. PubMed ID: 14564208; Bellini et al. 2003. PubMed ID: 17294699).

FOXC2 – Lymphedema-distichiasis (LD) Syndrome is an autosomal dominant form of primary lymphedema that presents with lymphedema of the lower extremities, a double row of eyelashes and a variable age of onset (Mansour et al. 2012. PubMed ID: 20301630). Patients may also have cleft palate, extradural cysts, cardiac defects, or photophobia. Other ocular findings may include: exotropia, ptosis as well as congenital ectropion and cataracts.

GATA2 – Several disorders are related to autosomal dominant pathogenic variations in the GATA2 gene. These disorders include Emberger syndrome (Ostergaard et al. 2011. PubMed ID: 21892158) and combined immunodeficiencies termed, dendritic cell, monocyte, B and NK lymphoid deficiency (aka DCML) (Dickinson et al. 2011. PubMed ID: 21765025), or monocytopenia and mycobacterial infection syndrome (aka MonoMAC) (Hsu et al. 2011. PubMed ID: 21670465). DCML/MonoMAC is characterized by decreased or absent dendritic cells, monocytes, B and natural killer (NK) cells, and moderately low T cell numbers. Patients have an increased susceptibility to disseminated nontuberculous mycobacterial infections, viral infections (HPV), and fungal infections (Vinh et al. 2010. PubMed ID: 20040766; Bigley et al. 2011. PubMed ID: 21242295). Emberger syndrome is characterized by primary lymphedema, deafness, and varying degrees of pancytopenia. Onset of Emberger syndrome and DCML/MonMac is usually in childhood followed by progression to myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) over decades. Pathogenic variants in the GATA2 gene have also been identified in families with hereditary MDS/AML, but with no other hematopoietic defects (Hahn et al. 2011. PubMed ID: 21892162).

GJA1 – Brice et al. 2013 reported a three generation family with a GJA1 variant c.617A>G (p.Lys206Arg) that segregated with autosomal dominant oculodentodigital dysplasia (ODDD) with primary lymphedema (Brice et al. 2013. PubMed ID: 23550541). In addition to lower extremity lymphedema, patients may display characteristics of ODDD which include a range of facial, eye, dental, and digit anomalies. GJA1 encodes a gap junction protein, connexin 43, that is important for lymphatic system function. Another gap junction protein associated with proper lymphatic function is connexin 47 which is encoded by GJC2.

GJC2 – Autosomal dominant Lymphedema Type 1C presents most commonly with lower limb lymphedema. Onset ranges from birth to 40 years with most experiencing symptoms within the first or second decades (Ostergaard et al. 2011. PubMed ID: 21892158). The severity of the disease varies from mild lower limb swelling to edema in all four limbs. More severe cases may involve skin infections and cellulitis (Ferrell et al. 2010. PubMed ID: 20537300; Ostergaard et al. 2011. PubMed ID: 21892158). Pathogenic variants in the GJC2 gene are also associated with Pelizaeus-Merzbacher-Like disease (PMLD). Patients with PMLD have reduced formation of myelin in the brain (Van der Knaap et al. 1999. PubMed ID: 10540652) and present with nystagmus, hypotonia, motor delay, cerebellar ataxia, and spasticity (Uhlenberg et al. 2004. PubMed ID: 15192806).

KIF11 – Microcephaly, primary lymphedema, and chorioretinal dysplasia (MLCRD) is inherited in an autosomal dominant manner with lymphedema typically confined to the dorsa of the feet (Ostergaard et al. 2012. PubMed ID: 22284827). Patients display mild to severe microcephaly with characteristic facial features including palpebral fissures, broad nose with rounded tip, long philtrum with thin upper lip, and prominent chin and ears. Eye abnormalities may or may not be present and include chorioretinopathy, retinal folds, microphthalmia, and astigmatism. Features of MLCRD overlap those of chorioretinal dysplasia, microcephaly, and mental retardation (CDMMR) and it has been suggested that these disorders represent a single disorder with a broad spectrum of clinical features (Ostergaard et al. 2012. PubMed ID: 22284827).

PIEZO1 – Pathogenic variants in PIEZO1 have been reported in patients with autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis (hereditary lymphedema III, LMPH3, Fotiou et al. 2015. PubMed ID: 26333996). LMPH3 is characterized by widespread lymphedema around the body and non-immune hydrops fetalis resulting in death or that resolved postnatally, but was followed by childhood lymphedema. Other characteristics such as severe facial cellulitis and spherocytosis are also associated with LMPH3, and patients are reported to have normal intelligence (Fotiou et al. 2015. PubMed ID: 26333996).

PTPN14 – Pathogenic variants in PTPN14 are associated with autosomal recessive Choanal atresia and lymphedema. The PTPN14 protein is part of a larger protein complex including VEGFC and VEGFR3 proteins that is essential for lymphangiogenesis (Au et al. 2010. PubMed ID: 20826270). Pathogenic variants in PTPN14 have been reported in only a few families and comprise a small insertion and a deletion of an exon (Au et al. 2010. PubMed ID: 20826270; see also Bordbar et al. 2017. Meta Gene 14). Additional clinical characteristics may include high-arched palate and pericardial effusion with early onset edema of the lower extremities.

SOX18 – Lymphedema with Hypotrichosis and Telangiectasia displays both autosomal recessive and dominant inheritance (Irrthum et al. 2003. PubMed ID: 12740761). Lymphedema is present in the legs of patients or is more generalized. Onset of lymphedema is birth to puberty. Hypotrichosis (sparse hair) is present at birth or develops in infancy. Hypotrichosis includes absence of eyebrows and eyelashes. Telangiectasia (abnormal dilation of blood vessels leading to focal red lesions) is present on palms, soles, scalp and legs.

VEGFC – Pathogenic variants in VEGFC have been reported in patients with autosomal dominant Milroy-like disease (Gordon et al. 2013. PubMed ID: 23410910; Balboa-Beltran et al. 2014. PubMed ID: 24744435). Pathogenic variants in FLT4 are the primary cause of Milroy disease and account for ~ 70% of cases whereas VEGFC variants have been reported in only a few patients. Milroy and Milroy-like disease are characterized by lower limb lymphedema, prominent veins in lower limbs, and dysplastic toenails. Changes in the skin of affected areas may include hyperkeratosis, papillomatosis, fibrosis, and cellulitis (Gordon et al. 2013. PubMed ID: 23410910; Balboa-Beltran et al. 2014. PubMed ID: 24744435).

For more information about mutation spectra in these genes and the molecular biology of gene products, see the individual gene test descriptions.

The incidence of lymphedema (primary or secondary) is uncertain, though one estimate suggests approximately 1.4 per 1000 people (Rockson and Rivera 2008. PubMed ID: 18519968). Primary lymphedema is reportedly rare in children and affects approximately 1.2 per 100,000 persons under 20 years of age (Smeltzer et al. 1985. PubMed ID: 4022694; Sitzia et al. 1998. PubMed ID: 9919113). The percentages of lymphedema cases that can be attributed to each of the known hereditary lymphedema genes is currently unclear.

Large deletions and duplications are not common in the lymphedema panel genes. Missense and nonsense variants are the primary causes of disease among most of the lymphedema genes. Large deletions or duplications have been reported for the GATA2, FOXC2, and GJC2 genes, but are rare and comprise a small fraction of the reported variants for these genes. For the PTPN14 gene, one small insertion and one large deletion have been reported. No large deletions or duplications have been reported for the other genes in the lymphedema panel.

This test is performed using Next-Gen sequencing with additional Sanger sequencing as necessary.

This panel typically provides 97.1% coverage of all coding exons of the genes plus 10 bases of flanking noncoding DNA in all available transcripts along with other non-coding regions in which pathogenic variants have been identified at PreventionGenetics or reported elsewhere. We define coverage as ≥20X NGS reads or Sanger sequencing. PGnome panels typically provide slightly increased coverage over the PGxome equivalent. PGnome sequencing panels have the added benefit of additional analysis and reporting of deep intronic regions (where applicable).

Dependent on the sequencing backbone selected for this testing, discounted reflex testing to any other similar backbone-based test is available (i.e., PGxome panel to whole PGxome; PGnome panel to whole PGnome).