Epidermolysis Bullosa (EBS) and Related Disorders Panel

Epidermolysis Bullosa (EB) is a clinically and genetically heterogeneous skin separation disorder. Based on the level of skin separation, it can be divided into four major subgroups: EB simplex (EBS), Junctional Epidermolysis Bullosa (JEB), Dystrophic Epidermolysis Bullosa (DEB), and Kindler Syndrome (Fine et al. 2014. PubMed ID: 24690439).

Epidermolysis Bullosa Simplex (EBS) is a skin separation disorder characterized by congenital blistering, skin atrophy, and skin fragility caused by minor physical trauma (Fine et al. 2008. PubMed ID: 18374450). Pathogenic variants in KRT5 cause epidermolysis bullosa simplex of the following subtypes: Dowling-Degos disease, epidermolysis bullosa simplex with migratory circinate erythema, epidermolysis bullosa simplex with mottled pigmentation epidermolysis bullosa simplex Dowling-Meara type, epidermolysis bullosa simplex Koebner type and epidermolysis bullosa simplex Weber-Cockayne type.

Junctional epidermolysis bullosa (JEB) is one of the four major types of epidermolysis bullosa (EB), in which blisters develop within the mid portion or junction (lamina lucida). Morphologically, it can be divided into generalized JEB and localized JEB, which includes junctional epidermolysis bullosa and epidermolysis bullosa with pyloric atresia (Fine et al. 2014. PubMed ID: 24690439). Other features in this syndrome include congenital pyloric atresia, ureterovesical stenosis, pyelonephrosis, esophageal atresia, congenital cutis aplasia, and arthrogryposis (Fine et al. 2008. PubMed ID: 18374450; Varki et al. 2006. PubMed ID: 16473856; Pfendner et al. 2014. PubMed ID: 20301304).

Dystrophic Epidermolysis Bullosa (DEB) is characterized by blister formation induced by mild trauma. Autosomal recessive DEB (RDEB) can be further divided in to severe generalized RDEB (also called Hallopeau-Siemens type) and generalized, not severe RDEB (also called non-Hallopeau-Siemens type). Severe generalized RDEB is the most severe form of DEB, where blisters may develop in the neonatal period and affect the whole body. Erosions and fusions can lead to restrictions in oral, corneal, esophageal, and lung tissue. Pseudosyndactly caused by extensive blistering and erosion can be a hallmark of severe generalized RDEB. Autosomal dominant DEB (DDEB) is the second most common subtype of epidermolysis bullosa, where the dystrophic nails may be the only manifestation in some DDEB patients, and blisters tend to be mild and localized to hands, knees and elbows. DEB patients are at high risk to develop squamous cell carcinoma (Fine et al. 2008. PubMed ID: 18374450; Pfendner et al. 2016. PubMed ID: 20301481; Intong et al. 2012. PubMed ID: 22137229). In addition to DEB, deleterious variants in COL7A1 also cause other DEB-related disorders including epidermolysis bullosa BART type, epidermolysis bullosa pruriginosa, epidermolysis bullosa pretibial, isolated toenail dystrophy, and transient bullous dermolysis of the newborn.

Kindler syndrome is the fourth major type of epidermolysis bullosa, characterized by congenital blistering, skin atrophy, photosensitivity, and skin fragility (Fine et al. 2008. PubMed ID: 18374450). Other features include palmoplantar keratoderma, gingival erosions, and ocular, esophageal, gastrointestinal and urogenital involvement. Patients with Kindler syndrome are also at risk to develop mucocutaneous malignancy (Lai-Cheong et al. 2010. PubMed ID: 19945624).

This panel tests the following genes that contribute to epidermolysis bullosa and related disorders: COL7A1, COL17A1, DSP, DST, FERMT1, ITGA3, ITGA6, ITGB4, JUP, LAMA3, LAMB3, LAMC2, PKP1, KRT10, KRT14, KRT5, PLEC and TGM5.

Genes involved in autosomal recessive conditions: DST, FERMT1, ITGA6, LAMA3, LAMC2, PKP1 and TGM5.

Genes involved in both autosomal dominant and autosomal recessive conditions: COL7A1, COL17A1, DSP, ITGB4, JUP, LAMB3, KRT14, KRT5, and PLEC.

Epidermolysis bullosa simplex (EBS): EBS is caused by variants in KRT5 and KRT14, which are usually inherited in an autosomal dominant manner; however, a few recessive cases have also been reported. Biallelic pathogenic variants in TGM5 also cause EBS (Pfendner et al. 2016. PubMed ID: 20301481). In the epidermis of the skin, keratin 5 protein partners with keratin 14 protein to form keratin intermediate filaments, which attach keratinocytes together and anchor the epidermis to underlying layers of skin.

Pathogenic variants in KRT5 cluster in exons 1, 5, and 7. The majority of the reported point variants are missense (except for 7 nonsense variants). About 20 small deletions, insertions, indels and splicing variants have been reported (Human Gene Mutation Database); Arin et al. 2010. PubMed ID: 20199538; Bolling et al. 2011. PubMed ID: 21375516). Three large deletions involving KRT5 have been reported (Human Gene Mutation Database).

To date, about 117 KRT14 pathogenic variants have been documented in Human Gene Mutation Database. The common pathogenic variants in KRT14 cluster in exons 1, 4, and 6. Pathogenic variants include missense (65%), nonsense (10%), small deletions/ insertions (15%) and splicing variants (3%). Only three large insertions and one large genomic rearrangement involving KRT14 have been reported (Human Gene Mutation Database).

The majority of TGM5 pathogenic variants are missense (15/21). Additionally, a small number of nonsense, small deletions, duplications and indels have been reported (Human Gene Mutation Database).

Pathogenic variants in KRT10 cause epidermolytic heperkeratosis (Makino et al. 2012. PubMed ID: 21463361) a disorder with similar skin phenotype to epidermolysis bullosa.

Junctional epidermolysis bullosa (JEB) is an autosomal recessive disorder caused by pathogenic variants in the LAMA3, COL17A, LAMB3, and LAMC2 genes. Pathogenic variants in LAMB3, LAMA3, COL17A1 and LAMC2 account for ~70%, 12%, 9%, and 9% of pathogenic variants reported in JEB cases, respectively. Most known pathogenic variants (>80%) in these four genes are truncating (nonsense, frameshift and splicing). Generally, splicing variants result in relatively milder JEB, and nonsense variants in both alleles tend to cause severe forms of JEB. One study reported that the variant c.1903C>T, p. Arg635* comprised ~40% of mutant alleles identified in LAMB3 gene (Varki et al. 2006. PubMed ID: 16473856). Also, ethnically-related LAMB3 variants have also been described (such as p.Arg635* and c.727C>T, p.Gln243* in Europeans, and c.124C>T, p.Arg42* in Hispanics and African Americans). The c.151dupG in exon 39 of LAMA3 was found in LOC syndrome and c.1981C>T, p.Arg661* (also referred as Arg650* in exon 54 of LAMA3) was predominantly seen in Pakistan JEB patients. A heterozygous variant c.1880G>T, p.Gly627Val in COL17A1 was reported in an autosomal dominant JEB patient with an enamel defect (Almaani et al. 2009. PubMed ID: 19120338). A variant in COL17A1 was also identified in a patient affected with epidermolysis bullosa simplex (Pasmooij et al. 2004. PubMed ID: 15377356). Furthermore, germline mosacism and uniparental disomy were reported in JEB cases involving the three laminin-332 genes (Varki et al. 2006. PubMed ID: 16473856; Pfendner et al. 2014. PubMed ID: 20301304;, Kiritsi et al. 2011. PubMed ID: 21357940). ITGA3 pathogenic variants cause pulmonary fibrosis and junctional epidermolysiss bullosa (Has et al. 2012. PubMed ID: 22512483; Yalcin et al. 2015. PubMed ID: 25810266). Epidermolysis bullosa with pyloric atresia is an autosomal recessive disorder caused by pathogenic variants in the ITGB4, ITGA6, and PLEC genes.

Dystrophic Epidermolysis Bullosa (DEB) is mainly caused by pathogenic variants in the COL7A1 gene. To date, more than 700 distinct pathogenic variants have been documented in (Human Gene Mutation Database) including missense, nonsense, splicing variants and small insertions/deletions. Only 14 large genome rearrangements involving COL7A1 were reported. In addition, one DEB case with maternal COL7A1 UPD was reported (Fassihi et al. 2006. PubMed ID: 16710310), and a case of a de novo variant in recessive DEB (Lee et al. 2016. PubMed ID: 26940370). Approximately 75% of the dominant DEB pathogenic variants occur in exons 73-75; while recessive DEB are caused by truncated pathogenic variants scattered throughout COL7A1 (Varki et al. 2006. PubMed ID: 16473856; Pfendner et al. 2016. PubMed ID: 20301481).

Kindler syndrome is an autosomal recessive disorder caused by pathogenic variants in FERMT1. To date, more than 80 distinct pathogenic variants have been documented (Human Gene Mutation Database). The majority are truncating variants. Only 8 large deletions involving FERMT1 have been reported (Lai-Cheong et al. 2010. PubMed ID: 19945624; Chmel et al. 2015. PubMed ID: 26083552).

Pathogenic variants in JUP cause autosomal dominant Arrhythmogenic right ventricular dysplasia 12 and autosomal recessive Naxos disease (McKoy et al. 2000. PubMed ID: 10902626).

Pathogenic variants in DST cause autosomal recessive Epidermolysis bullosa simplex and autosomal recessive hereditary sensory and autonomic neuropathy, type VI (Groves et al. 2010. PubMed ID: 20164846; Liu et al. 2012. PubMed ID: 22113475; Turcan et al. 2017. PubMed ID: 28558912).

Pathogenic variants in DSP gene mainly cause autosomal dominant Arrhythmogenic right ventricular dysplasia 8. This gene has also been reported to be involved with autosomal recessive cardiomyopathy dilated with woolly hair, autosomal recessive Epidermolysis bullosa lethal acantholytic, and autosomal recessive skin fragility-woolly hair syndrome (Norgett et al. 2006. PubMed ID: 16628197; Zhou et al. 2015. PubMed ID: 25765472).

Pathogenic variants in KRT10 cause epidermolytic hyperkeratosis and epidermolytic ichthyosis (Makino et al. 2012. PubMed ID: 21463361; Abdul-Wahab et al. 2016. PubMed ID: 26338057). Mostly missense variants in KRT10 have been reported to be causative for epidermolytic hyperkeratosis. Other reported variants include nonsense, splicing, small frameshift deletion and duplications (Makino et al. 2012. PubMed ID: 21463361; Human Gene Mutation Database).

Pathogenic variants in the COL7A1 gene can be found in ~95% of Dystrophic Epidermolysis Bullosa patients diagnosed via skin biopsy (Kern et al. 2006. PubMed ID: 16484981; Pfendner et al. 2016. PubMed ID: 20301481).

In a retrospective study, all 76 studied patients diagnosed with severe Junctional Epidermolysis Bullosa based on skin biopsies were found to have pathogenic variants in one of the LAMA3, COL17A, LAMB3, or LAMC2 genes (Hammersen et al. 2016. PubMed ID: 27375110). Pathogenic variants in ITGB4, PLEC, and ITGA6 account for ~60%, 15%, and 5%, respectively, of pathogenic variants reported in Epidermolysis Bullosa with Pyloric Atresia cases (Pfendner et al. 2017. PubMed ID: 20301336).

KRT5 and KRT14 pathogenic variants together account for ~75% of Epidermolysis Bullosa Simplex cases diagnosed with skin biopsy (Arin et al. 2010. PubMed ID: 20199538; Bolling et al. 2011. PubMed ID: 21375516). The percentage of cases due to each gene is approximately equal.

Ashton et al. found 17 different loss-of-function FERMT1 pathogenic variants in 41 clinically diagnosed Kindler syndrome families (Ashton et al. 2004. PubMed ID: 14987263).

In one study, the pathogenic variant (c.2038_2039delTG) in the JUP gene was detected in in all 19 Naxos patients of Greek origin (McKoy et al. 2000. PubMed ID: 10902626).

Pathogenic variants in the DSP gene were found in 16% of patients with clinical diagnosis of Arrhythmogenic right ventricular dysplasia (Bauce et al. 2005. PubMed ID: 15941723).

Only about 10 large genome rearrangements involving COL7A1 have been reported. In addition, one Dystrophic Epidermolysis Bullosa case with maternal COL7A1 Uniparental Disomy was reported (Fassihi et al. 2006. PubMed ID: 16710310; Human Gene Mutation Database).

Several large CNVs have been reported involving the FERMT1 gene (Chmel et al. 2015. PubMed ID: 26083552).

Only a few large CNVs involving the COL17A1, DSP, ITGB4, LAMB3, LAMC2, KRT14, PLEC, LAMA3, and KRT5 genes have been reported (Huber et al. 2002. PubMed ID: 11851893; Norgett et al. 2006. PubMed ID: 16628197; Schumann et al. 2013. PubMed ID: 23496044; Pulkkinen et al. 1995. PubMed ID: 7550237; Posteraro et al. 2004. PubMed ID: 15373767; Kopecková et al. 2016. PubMed ID: 26707537; Vahidnezhad et al. 2017. PubMed ID: 28830826; Has et al. 2017. PubMed ID: 28576738; Human Gene Mutation Database).

No large CNVs have been reported involving the DST, ITGA6, JUP, PKP1 genes.

Approximately 5% of pathogenic TGM5 variants cause epidermolysis bullosa (Pfendner et al. 2016. PubMed ID: 20301481).

To date, only 11 causative variants in ITGA3 have been detected in individuals with interstitial lung disease, nephrotic syndrome and epidermolysis bullosa (Yalcin et al. 2015. PubMed ID: 25810266; Has et al. 2012. PubMed ID: 22512483).

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

This panel provides 100% 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).