Primary features of Waardenburg syndrome (WS) may include distinctive facial abnormalities; unusually diminished pigmentation (hypopigmentation) of the hair, the skin, and/or the irides or the iris of both eyes (partial albinism); and/or deafness that is present at birth (congenital). However, as mentioned earlier, associated symptoms and findings may be extremely variable, including among affected members of the same family (kindred). For example, while some affected individuals may have only one characteristic feature, others may have several abnormalities associated with the disorder.
In some individuals with WS, there is abnormal sideways (lateral) displacement of the inner angles (canthi) of the eyes formed by the junction of the upper and lower eyelids (dystopia canthorum). In addition, the condition may be associated with unusually low (inferior) openings to the tear (lacrimal) ducts and an increased susceptibility to infections of the lacrimal sacs (dacryocystitis). (Each inner canthus opens into a small space that contains the opening to a lacrimal duct.) Due to dystopia canthorum, affected individuals may have an abnormally wide, high nasal bridge and underdeveloped nasal “wings” (hypoplastic nasal alae), resulting in narrow nostrils. In addition, in some cases, the eyebrows may be unusually bushy and/or may grow together (synophrys). Rarely, affected individuals also have widely spaced eyes (ocular hypertelorism). As mentioned previously, researchers have described different forms of WS based upon certain symptoms and specific genetic findings. WS type II (WS2) is distinguished from WS type I (WS1) by the absence of dystopia canthorum.
In some individuals with WS, additional facial abnormalities may be present. These may include an unusually rounded nasal tip that may be slightly upturned; abnormal “smoothness” of the vertical groove of the upper lip (philtrum); full lips; and/or mild protrusion of the lower jaw (mandibular prognathism). There have also been a few reports in which the disorder has been associated with incomplete closure of the roof of the mouth (cleft palate) and/or an abnormal groove in the upper lip (cleft lip).
WS is often associated with pigmentary abnormalities due to deficiency of the pigment melanin. Some with the disorder have a white forelock (poliosis) at birth that tends to disappear with age or patches of white hair other than a forelock. (There have also been cases in which a black rather than a white forelock is present.) The eyebrows, eyelashes, and scalp hair may become prematurely gray or white (beginning as early as mid-childhood, adolescence, or early adulthood). In addition, some affected individuals have irregular patchy skin regions that lack pigmentation (leukoderma or vitiligo), particularly on the face and arms. WS may also be associated with underdevelopment (hypoplasia) of the connective tissue fibers that comprise most of the colored region (iris) of both eyes (irides). As a result, affected individuals may have unusually pale blue eyes or differences in the pigmentation of the two irides or within different areas of the same iris (heterochromia irides). For example, the iris of one eye may be blue while the other has a different color or one or both irides may seem unusually “mottled” in appearance. Some reports suggest that heterochromia irides may be more frequent in WS2 while the presence of a white forelock and depigmented skin patches are more common in those with WS1.
Some individuals with WS are also affected by congenital deafness. Such hearing impairment appears to result from abnormalities or absence of the organ of Corti, a structure within the hollow, coiled passage of the inner ear (cochlea). The organ of Corti contains minute hair cells that convert sound vibrations into nerve impulses, which are then transmitted via the auditory nerve (vestibulocochlear nerve) to the brain. Abnormalities of the organ of Corti may prevent the transmission of such nerve impulses, resulting in hearing impairment (known as sensorineural or cochlear deafness). In most affected individuals with WS, congenital sensorineural deafness affects both ears (bilateral). However, in rare cases, only one side may be affected (unilateral). Evidence suggests that congenital sensorineural deafness is more frequently associated with WS2 than WS1.
In some cases, characteristic facial, eye (ocular), and hearing (auditory) features of WS may occur in association with bilateral malformations of the arms and hands (upper limbs). This form of the disorder, which has been described as a severe presentation of WS1, is sometimes referred to as WS type III (WS3), Klein-Waardenburg syndrome, or Waardenburg syndrome with upper limb anomalies. Bilateral defects may include underdevelopment (hypoplasia) and abnormal shortness of the upper limbs; abnormal bending of certain joints of the fingers in fixed positions (flexion contractures); fusion of wrist (carpal) bones; and/or webbing or fusion (syndactyly) of certain fingers. In some cases, other skeletal abnormalities may be present, such as abnormal elevation of the shoulder blades (Sprengel deformity).
A fourth form of WS has also been described in which primary features of WS occur in association with Hirschsprung disease. This form of the disorder may be referred to as WS4, Waardenburg-Shah syndrome, or Waardenburg-Hirschsprung disease. Hirschsprung disease (also known as aganglionic megacolon) is a gastrointestinal (GI) disorder characterized by absence of certain nerve cell bodies (ganglia) in the smooth muscle wall within a region of the large intestine (i.e., colon). As a result, there is absence or impairment of the involuntary, rhythmic contractions that propel food through the GI tract (peristalsis). Associated symptoms and findings may include an abnormal accumulation of feces within the colon; widening of the colon above the affected segment (megacolon); abdominal bloating (distension); vomiting; lack of appetite (anorexia); failure to grow and gain weight at the expected rate (failure to thrive); and/or other abnormalities.
Rare cases of WS4 have been described in which affected individuals have also had neurologic symptoms due to abnormalities of the brain and spinal cord (central nervous system). In such instances, additional findings have included growth restriction; abnormally diminished muscle tone (hypotonia); flexion or extension of certain joints in various fixed postures (arthrogryposis); and/or other abnormalities.
In most cases, Waardenburg syndrome type I (WS1) and type II (WS2) are inherited as autosomal dominant traits with variable penetrance and expressivity. Some cases of Waardenburg syndrome type III (WS3) and type IV (WS4) appear to have an autosomal recessive pattern of inheritance. Mutations in the EDN3, EDNRB, MITF, PAX3 and SOX10 genes cause Waardenburg syndrome.
In dominant disorders, a single copy of the disease gene (received from either the mother or father) will be expressed “dominating” the other normal gene, potentially resulting in the appearance of the disease. The risk of transmitting the disease gene from parent to offspring is 50 percent for each pregnancy regardless of the sex of the resulting child. In autosomal dominant disorders with variable penetrance and expressivity, manifestations of the disorder may not be present in all those who inherit the altered (mutated) gene for the disease. In those who do develop symptoms, the specific characteristics that are manifested may vary greatly in range and severity from case to case.
In some individuals with WS1 or WS2, there may be no apparent family history of the disorder. In such cases, researchers indicate that the disorder may sometimes result from new genetic changes (mutations) that occur spontaneously (sporadically) for unknown reasons. (In other instances, an apparent lack of a positive family history may be due to incomplete penetrance and/or variable expressivity as discussed above.) Evidence suggests that new (sporadic) mutations for WS1 may be associated with advanced age of the father (advanced paternal age).
Researchers have located a gene responsible for WS1–known as the “PAX3″ gene–on the long arm (q) of chromosome 2 (2q35). Multiple specific mutations of the PAX3 gene have been identified in different individuals and families (kindreds) affected by WS1. Chromosomes are found in the nucleus of all body cells. They carry the genetic characteristics of each individual. Pairs of human chromosomes are numbered from 1 through 22, with an unequal 23rd pair of X and Y chromosomes for males and two X chromosomes for females. Each chromosome has a short arm designated as “p” and a long arm identified by the letter “q.” Chromosomes are further subdivided into bands that are numbered. Therefore, “chromosome 2q35″ refers to band 35 on the long arm of chromosome 2.
The function of the PAX3 gene remains unknown. However, some researchers suggest that PAX3 helps to regulate the functioning of another gene (known as “MITF”) that has been implicated in some cases of WS2.
In some families with WS2, researchers have determined that the disorder results from mutations of a gene designated “MITF” (for “microphthalmia-associated transcription factor”) on chromosome 3 (3p14.1-p12.3). WS2 due to MITF gene mutations is known as “WS2A.” However, in other families, genetic analysis has demonstrated that WS2 does not result from mutations of the MITF gene. Thus, researchers indicate that there is at least one other genetic form of WS2, which they have designated “WS2B.” SOX10 mutations and deletions are also responsible for WS2.
The MITF gene is thought to regulate the production of a protein that plays an essential role in the development of certain pigment (melanin)-producing cells known as melanocytes. Absence or impaired functioning of melanocytes affects pigmentation of the eyes, skin, and hair and has been shown to affect hearing function of the cochlea of the inner ear. Thus, investigators indicate that mutations of the MITF gene may result in abnormalities of melanocyte development, leading to the reduced pigmentation (hypopigmentation) and hearing loss potentially associated with WS2. As mentioned above, evidence suggests that the MITF gene is regulated by the PAX3 gene. Therefore, researchers indicate that mutations of the PAX3 gene may cause failed regulation of the MITF gene, potentially leading to the pigmentary and hearing abnormalities also seen in WS1.
As with WS1, Waardenburg syndrome type III (WS3) may result from certain mutations of the PAX3 gene that may be inherited as an autosomal dominant trait or occur sporadically. In addition, some investigators suggest that WS3 may sometimes result from mutations of the PAX3 gene of both chromosomes (homozygosity). For example, in a large family (kindred) in which several members were affected by WS1, one child was diagnosed with severe WS3. The parents, who were closely related by blood (consanguineous), were both affected by mild WS1. Evidence suggested that siblings with WS1 inherited one mutated copy of the PAX3 gene (heterozygosity) from one parent, whereas the child with WS3 inherited mutated copies of the PAX3 gene from both parents. In other individuals with WS3, the disorder has been shown to result from deletion of the PAX3 gene and adjacent genes on chromosome 2.
Waardenburg syndrome type IV (WS4), also known as Waardenburg-Hirschsprung disease, has been shown to result from mutations of several different genes that have also been implicated in causing some isolated cases of Hirschsprung disease. These include the EDNRB gene (mapped to chromosome 13q22), the EDN3 gene (chromosome 20q13.2-q13.3), or the SOX10 gene (chromosome 22q13).
Researchers have identified mutations of the EDNRB gene or the EDN3 gene on both chromosomes (homozygosity) in some individuals with WS4, whereas single mutations of these genes (i.e., heterozygosity) may result in Hirschsprung disease alone. Therefore, researchers indicate that WS4 due to mutation of the EDNRB or EDN3 gene may be inherited as an autosomal recessive trait. In recessive disorders, the condition does not appear unless a person inherits the same defective gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease but usually will not show symptoms. The risk of transmitting the disease to the children of a couple, both of whom are carriers for a recessive disorder, is 25 percent. Fifty percent of their children risk being carriers of the disease but generally will not show symptoms of the disorder. Twenty-five percent of their children may receive both normal genes, one from each parent, and will be genetically normal (for that particular trait). The risk is the same for each pregnancy.
In contrast, evidence suggests that a single mutated copy of the SOX10 gene may result in WS4. Thus, WS4 due to mutation of the SOX10 gene may be inherited as an autosomal dominant trait or may appear to occur sporadically due to new gene mutations. Together with the PAX3 gene, the SOX10 gene is thought to play some role in activating expression of the MITF gene. As mentioned above, mutations of the PAX3 gene have been identified in individuals with WS1 and WS3. MITF gene mutations have been implicated in some cases of WS2 (i.e., WS2A). Thus, researchers suggest that mutations leading to alterations in the interaction between the PAX3, MITF, and SOX10 genes may result in the pigmentary and hearing abnormalities seen in the Waardenburg syndromes. In addition, because some individuals with WS4 due to SOX10 mutations have had Hirschsprung disease as well as certain abnormalities of the central nervous system (CNS), the SOX10 gene is also thought to play some role in the early development of the autonomic nervous system and the CNS, particularly glial cells. The autonomic nervous system helps to regulate involuntary functions of the body. Glial cells are connective tissue cells of the CNS that hold together and protect certain nerve cells (neurons).
Waardenburg syndrome (WS) is named after the investigator (PJ Waardenburg) who first precisely described the disorder in 1951. At least 1,400 cases have since been recorded in the medical literature. Evidence suggests that WS may have a frequency of approximately one in 40,000 births and account for about two to five percent of cases of congenital deafness. The disorder appears to affect males and females relatively equally.
Waardenburg syndrome (WS) may be diagnosed at birth or early childhood (or, in some cases, at a later age) based upon a thorough clinical evaluation, identification of characteristic physical findings, a complete patient and family history, and various specialized studies. For example, in those with suspected WS, diagnostic evaluation may include use of a caliper to measure the distances between the inner angles of the eyes (inner canthi), the outer angles of the eyes (outer canthi), and the pupils (interpupillary distances). (A caliper is an instrument with two hinged, movable, curved arms used to measure thickness or diameter.) Researchers indicate that obtaining and evaluating a composite of these measurements (i.e., using a predefined biometric index known as the “W-index”) may sometimes be helpful in confirming the presence or absence of dystopia canthorum, a finding that may suggest WS1.
Additional diagnostic studies may be conducted to help detect or characterize certain abnormalities potentially associated with WS. Such studies may include examination with an illuminated microscope to visualize internal structures of the eyes (slit-lamp examination); specialized hearing (auditory) tests; and/or advanced imaging techniques, such as to evaluate inner ear abnormalities, skeletal defects (e.g., seen in WS3), Hirschsprung disease (e.g., seen in WS4), etc. For example, researchers indicate that computed tomography (CT) scanning may help to characterize inner ear defects responsible for congenital sensorineural deafness. (During CT scanning, a computer and x-rays are used to create a film showing cross-sectional images of internal structures.) In selected cases, diagnostic evaluation may also include the removal (biopsy) and microscopic examination of certain tissue samples, such as rectal biopsies to help confirm Hirschsprung disease. In some instances, additional diagnostic studies may also be recommended.
The treatment of WS is directed toward the specific symptoms that are apparent in each individual. Such treatment may require the coordinated efforts of a team of medical professionals, such as physicians who specialize in skin disorders (dermatologists); eye specialists (ophthalmologists); hearing specialists; physicians who diagnose and treat disorders of the skeleton, joints, muscles, and related tissues (orthopedists); physicians who specialize in diseases of the digestive tract (gastroenterologists); speech-language pathologists; physical therapists; and/or other health care professionals.
Early recognition of sensorineural deafness may play an important role in ensuring prompt intervention and appropriate supportive management. In some instances, physicians may recommend treatment with a cochlear implant, a device in which electrodes implanted in the inner ear stimulate the auditory nerve to send impulses to the brain. In addition, early, special instruction may be recommended to assist in the development of speech and certain methods (e.g., sign language, lip reading, the use of communication devices, etc.) that may aid communication.
Because individuals with pigmentary abnormalities of the skin may be prone to sunburns and a risk of skin cancer, physicians may recommend avoiding direct sunlight, using sunscreen with a high sun protection factor (SPF), wearing sunglasses and coverings that help to protect against the sun (e.g., hats, long sleeves, pants, etc.), and following other appropriate measures. For those with diminished pigmentation of the irides, lateral displacement of the inner angles of the eyes (dystopia canthorum), and/or other associated ocular abnormalities, ophthalmologists may also recommend certain supportive measures. These may include the use of specially tinted glasses or contact lenses (e.g., to help reduce possible sensitivity to light), measures to help prevent or treat infection, or other preventive or therapeutic steps.
In individuals with upper limb abnormalities, treatment may include physical therapy and various orthopedic techniques, potentially including surgical measures. In addition, surgery may sometimes be recommended to help treat other abnormalities that may be associated with the disorder. The specific surgical procedures performed will depend upon the severity and location of the anatomical abnormalities, their associated symptoms, and other factors.
For example, for affected individuals with Hirschsprung disease, treatment may require removal of the affected intestinal region and surgical “rejoining” of healthy intestinal areas. In some instances, before surgical correction of the condition, treatment may require the creation of an artificial outlet for the colon through an opening in the abdominal wall (i.e., a temporary colostomy).
Additional supportive services that may be beneficial for some affected individuals include special education and/or other medical, social, or occupational services. Genetic counseling will also be of benefit for affected individuals and their families. Other treatment for this disorder is symptomatic and supportive.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. Government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
Tollfree: (800) 411-1222
TTY: (866) 411-1010
For information about clinical trials sponsored by private sources, contact:
For information about clinical trials conducted in Europe, contact:
Contact for additional information about Waardenburg syndrome:
Waardenburg Syndrome Resources(Please note that some of these organizations may provide information concerning certain conditions potentially associated with this disorder [e.g., hearing impairment, eye abnormalities, hypopigmentation, Hirschsprung's disease, etc.].)
Gorlin RJ, et al., eds. Syndromes of the Head and Neck. 5th ed. New York, NY: Oxford University Press; 2010:1369.
Jones KL. Smith’s Recognizable Patterns of Human Malformation. 6th ed. Philadelphia, PA: W.B. Saunders Company; 2006:278-79.
Behrman RE, et al., eds. Nelson Textbook of Pediatrics. 17th ed. Philadelphia, PA: W.B. Saunders Company; 2004:405,2091,2179.
Buyse ML. Birth Defects Encyclopedia. Dover, MA: Blackwell Scientific Publications, Inc.; 1990:79-80, 1773-74.
Zaman A, Capper R, Daddoo W. Waardenburg syndrome: more common than you think! Clin Otolaryngol. 2015;40(1):44-8.
Arimoto Y, Namba K, Nakano A, Matsunaga T. Chronic constipation recognized as a sign of a SOX10 mutation in a patient with Waardenburg syndrome. Gene. 2014;540(2):258-62.
Jelena B, Christina L, Eric V, Fabiola QR. Phenotypic variability in Waardenburg syndrome resulting from a 22q12.3-q13.1 microdeletion involving SOX10. Am J Med Genet A. 2014;78(6):1512-9.
Zhang H, Chen H, Luo H, et al. Functional analysis of Waardenburg syndrome-associated PAX3 and SOX10 mutations: report of a dominant-negative SOX10 mutation in Waardenburg syndrome type II. Hum Genet. 2012;131(3):491-503.
Chaoui A, Watanabe Y, Touraine R, et al. Identification and functional analysis of SOX10 missense mutations in different subtypes of Waardenburg syndrome. Hum Mut. 2011;32:1436-49.
Tamayo ML, Gelvez N, Rodriguez M, et al. Screening program for Waardenburg syndrome in Colombia: clinical definition and phenotypic variability. Am J Med Genet A. 2008;146A:1026-31.
Iso M, Fukami M, Horikawa R, Azuma N, Kawashiro N, Ogata T. SOX10 mutation in Waardenburg syndrome type II. Am J Med Genet A. 2008;146A:2162-3.
Bondurand N, Dastot-Le Moal F, Stanchina L, et al. Deletions at the SOX10 gene locus cause Waardenburg syndrome types 2 and 4. Am J Hum Genet. 2007;81:1169-85.
Milunsky JM, Maher TA, Ito M, Milunsky A. The value of MLPA in Waardenburg syndrome. Genet Test. 2007;11:179-82.
Madden C, Halsted MJ, Hopkin RJ, Choo DI, Benton C, Greinwald JH. Temporal bone abnormalities associated with hearing loss in Waardenburg syndrome. Laryngoscope. 2003;113:2035-41.
Wollnik B, Tukel T, Uyguner O, et al. Homozygous and heterozygous inheritance of PAX3 mutations causes different types of Waardenburg syndrome. Am J Med Genet A. 2003;122A:42-5.
Bondurand N, Pingault V, Goerich DE, et al. Interaction among SOX10, PAX3 and MITF, three genes altered in Waardenburg syndrome. Hum Mol Genet. 2000;9(13):1907-17.
Touraine RL, Attié-Bitach T, Manceau E, et al. Neurological phenotype in Waardenburg syndrome type 4 correlates with novel SOX10 truncating mutations and expression in developing brain. Am J Hum Genet. 2000;66(5):1496-503.
Inoue K, Tanabe Y, Lupski JR. . Myelin deficiencies in both the central and the peripheral nervous systems associated with a SOX10 mutation. Ann Neurol. 1999;46(3):313-18.
Tachibana M. A cascade of genes related to Waardenburg syndrome. J Investig Dermatol Symp Proc. 1999;4:126-29.
Watanabe A, et al. Epistatic relationship between Waardenburg syndrome genes MITF and PAX3. Nature Genet. 1998;18:283-86.
DeStefano AL, et al. Correlation between Waardenburg syndrome phenotype and genotype in a population of individuals with identified PAX3 mutations. Hum Genet. 1998;102:499-506.
Read AP, et al. Waardenburg syndrome. J Med Genet. 1997;34:656-65.
Nobukuni Y, et al. Analyses of loss-of-function mutations of the MITF gene suggest that haploinsufficiency is a cause of Waardenburg syndrome type 2A. Am J Hum Genet. 1996;59:76-83.
Tachibana M, et al. Ectopic expression of MITF, a gene for Waardenburg syndrome type 2, converts fibroblasts to cells with melanocyte characteristics. Nat Genet. 1996;14:50-54.
Wildhardt G, et al. Two different PAX3 gene mutations causing Waardenburg syndrome type I. Molec Cell Probes. 1996;10:229-31.
Tassabehji M, et al. The mutational spectrum in Waardenburg syndrome. Hum Molec Genet. 1995;4:2131-37.
Liu XZ, et al. Waardenburg syndrome type II: phenotypic findings and diagnostic criteria. Am J Med Genet. 1995;55:95-100.
Zlotogora J, et al. Homozygosity for Waardenburg syndrome. Am J Hum Genet. 1995;56:1173-78.
Baldwin CT, et al. Mutations in PAX3 that cause Waardenburg syndrome type I: ten new mutations and review of the literature. Am J Med Genet. 1995;58:115-22.
Reynolds JE, et al. Analysis of variability of clinical manifestations in Waardenburg syndrome. Am J Med Genet. 1995;57:540-47.
Farrer LA, et al. Locus heterogeneity for Waardenburg syndrome is predictive of clinical subtypes. Am J Hum Genet. 1994;55:728-37.
Tassabehji M, et al. PAX3 gene structure and mutations: close analogies between Waardenburg syndrome and the ‘splotch’ mouse. Hum Molec Genet. 1994;3:1069-74.
Hughes AE, et al. A gene for Waardenburg syndrome type 2 maps close to the human homologue of the microphthalmia gene at chromosome 3p12-p14.1. Nat Genet. 1994;7:509-12.
Pilz AJ, et al. Mapping of the human homologs of the murine paired-box-containing genes. Mammalian Genome. 1993;4:78-82.
Pasteris NG, et al. A chromosome deletion 2q35-36 spanning loci HuP2 and COL4A3 results in Waardenburg syndrome type III (Klein-Waardenburg syndrome) [abstract]. Am J Hum Genet. 1992;51 (suppl):A224.
Farrer LA, et al. Waardenburg syndrome (WS) type I is caused by defects at multiple loci, one of which is near ALPP on chromosome 2: first report of the WS Consortium. Am J Hum Genet. 1992;50:902-13.
Arias S, et al. Apparent non-penetrance for dystopia in Waardenburg syndrome type I, with some hints on the diagnosis of dystopia canthorum. J Genet Hum. 1978;26:103-31.
Arias S. Genetic heterogeneity in the Waardenburg syndrome. Birth Defects Orig Art Ser. 1971;VII: 87-101.
Waardenburg PJ. A new syndrome combining developmental anomalies of the eyelids, eyebrows and nose root with pigmentary defects of the iris and head hair and with congenital deafness. Am J Hum Genet. 1951;3:195.
Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Waardenburg Syndrome, Type 1; WS1. Entry No: 193500. Last Edited 04/03/2012. Available at: http://omim.org/entry/193500 Accessed May 19, 2015.
Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Waardenburg Syndrome, Type 4A; WS4A. Entry No: 277580. Last Edited 04/10/2015. Available at: http://omim.org/entry/277580 Accessed May 19, 2015.
Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Waardenburg Syndrome, Type 2A; WS2A. Entry No: 193510. Last Edited 03/15/2010. Available at: http://omim.org/entry/193510 Accessed May 19, 2015.
Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Waardenburg Syndrome, Type 2E; WS2E. Entry No: 611584. Last Edited 09/27/2013.Available at: http://omim.org/entry/611584 Accessed May 19, 2015.
Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Waardenburg Syndrome, Type 3; WS3. Entry No: 148820. Last Edited 03/15/2010. Available at: http://omim.org/entry/148820 Accessed May 19, 2015.