Waardenburg Syndrome

Etiology

WS is an autosomal dominant disorder. It is caused by mutations in different genes that affect the function of the neural crest.[5] For a child to have the disease, only one affected gene is necessary to pass on. The penetration and expression of different genes are also different. Mutations in the PAX3 gene at chromosome 2q is the cause of type 1 and type 3 syndrome. Mutation in MITF gene chromosome 3q causes type 2A WS. On the other hand, WS type 2B has gene mutations on chromosome 1q, and WS type 2C occurs due to mutation at chromosome 8q. Mutations in the SNAI2 gene at chromosome 8q causes WS Type 2D. Type 4 WS is due to mutations in the genes for one of its receptors, EDNRB or endothelin-3, which is autosomal recessive and a very rare variant.[6]

Epidemiology

The prevalence is variable around the world. An estimation of Waardenburg syndrome cases is  1/212,000 individuals in the general population of Netherland (low penetrance about 20%), but the entire syndrome is approximately 1/42,000 globally. Type 1 and 2 are commonly reported worldwide, while type 3 is very rarely reported.[7] Type 4 is reported in around 19% of cases of Waardenburg syndrome. In persons with deaf-mutism, the syndrome is observed in 0.9 to 2.8%. It affects all races worldwide with no gender difference. Waardenburg syndrome can be recognized immediately after birth, but skin changes occur with age. The clinical presentation of the syndrome varies, and most of the time, it is difficult to reach the final diagnosis to get an accurate prevalence.

Pathophysiology

WS is a genetic disorder with autosomal dominant inheritance.[5] There are various hypotheses proposed about the pathogenesis and to explain the different types and clinical features. One hypothesis suggests the abnormal development of the neural crest as causing the syndrome, and it is explained by the deficient neural crest theory. According to this hypothesis, there is an association of Waardenburg syndrome with Hirschsprung syndrome. The first arch syndrome also has features of Waardenburg syndrome.[6] 

A relationship between the intrauterine necrosis theory and Waardenburg syndrome with status dysraphicus has also been proposed. Among all these different hypotheses, none can explain all the features of Waardenburg syndrome. Individuals with deafness account for 50% of inherited causes, in which 70% have different single genes mutations that alone impair the functions of hearing. Syndromic deafness is also sometimes associated with other developmental abnormalities.[3] In Waardenburg syndrome, the genes which cause deafness include MITF and PAX3 in type 2 and type 1 syndrome, respectively. Type 4 WS is due to one of its receptors, EDNRB, or endothelin-3 gene mutations.[4]

Histopathology

The characteristic histopathological finding of Waardenburg syndrome is the absence of melanocytes (few dihydroxyphenylalanine positive cells are present). In the hypopigmented skin, melanosomes or indeterminate dendritic cells in the keratinocytes are present. Langerhans cells are normal in the epidermis, while on the edge of depigmented areas, the number of pigment cells is decreased with many abnormalities of nuclear and cytoplasm. Inside of vacuoles, a clear halo appears with some surrounding melanosomes.[8]

Histopathological findings of ears reveal atrophy of the spinal ganglion, the number of nerve fibers are also decreased with the absence organ of Corti.

History and Physical

Clinically, Waardenburg syndrome can be recognized by specific morphological features that appear after birth. These typical features are white forelock, broad nasal root, and the difference in the color of eyes. According to parents, the child usually does not respond to sounds. Every case of Waardenburg syndrome does not present with all clinical features. Based on genetic and clinical criteria, four types of WS are identified.[1]

Type 1 is characterized by dystopia canthorum, broad nasal root, short philtrum, and short retropositional maxilla. Patients with type 2 Waardenburg syndrome have normally located canthi, sensorineural deafness, and different colored irises. Type 3 WS (also called Klein-Waardenburg syndrome) has the same features as type-1, but musculoskeletal abnormalities are more prominent, like small carpal bones not differentiated fully, aplasia of first and second ribs, sacral cysts, abnormalities of the arms, and hypoplasia of muscles with syndactyly. Some cases of type 3 present with all primary features plus severe skeletal abnormalities, mental disability, and microcephaly. Type 4 WS (also called Shah-Waardenburg syndrome) has the same features as type 2 WS, but it is associated with congenital megacolon (Hirschsprung disease). Pigmentary abnormalities of WS affect skin, hair, and eyes. Skin abnormalities manifest as achromic spots and hyperpigmented macules over normal skin. Eye changes include heterochromia and bilateral isohypochromia. Waardenburg syndrome is a clinical diagnosis, but 2 criteria are used for diagnosis, i.e., major and minor criteria.[9]

Major criteria: Heterochromia, sensorineural deafness, white forelock, lateral displacement of inner canthi of eyes, and a first-degree relative with WS

Minor criteria: Broad nasal root, white macules/patches on the skin, synophrys, premature greying of the scalp hairs, and hypoplasia of nasal alae. For clinical diagnosis of Type 1 WS, two major or one minor and two minor criteria are needed.[10]

Evaluation

Waardenburg syndrome is mostly due to the genes changes in Type 1 and Type 3 due to the point mutations and can be detected by the use of multiplex ligation-dependent probe amplification in specific genes. Other tests include detecting the dystopia canthorum by three intraocular distances: 1)distance between angles of two inner canthi 2)the near papillary distance 3)distance between other canthi angles.[2]

There are no other specific radiological tests for Waardenburg syndrome.[1]

Treatment / Management

WS is a genetic disorder that currently has no definitive treatment.[11] In children with this disease, early diagnosis, and improvement of the deafness and hearing abnormalities are important for mental health development in order to decrease the sense of being ignored by others. The definitive/effective surgical treatment available is cochlear implantation. Sun protection is necessary for hypopigmented patches because these patients are susceptible to sun damage.[12] Genetic counseling is very important for these patients.

Differential Diagnosis

Differential diagnosis of Waardenburg syndrome include:

• Piebaldism: It is a genetic disorder characterized by depigmentation of skin and hair.[13]
• Tietz syndrome: A rare disorder present with musculoskeletal abnormalities.
• Oculocutaneous albinism: A disorder characterized by the absence of melanocytes. It clinically presents as depigmentation of skin and hairs with a change of eye color.
• Vogt-Koyanagi-Harada disease: Usually affects the skin, eyes, ear, and nervous system.
• Vitiligo: It clinically presents as multiple depigmented patches of skin and hair.

Prognosis

WS is a chronic condition. Life expectancy in children with Waardenburg syndrome is normal. Morbidity is related to the defect of neural crest-derived tissues, including mental disability, deafness and, ocular disorders (cataracts), skeletal anomalies, and psychiatric disorders.[14]

Complications

A complication of type 1 Waardenburg syndrome is blepharophimosis. Type 2 complications include sensorineural deafness (70%) Type 3 is associated with skeletal abnormalities, and the severe form presents with mental disability and microcephaly. Hirschsprung syndrome is the main complication of type 4 Waardenburg syndrome.[15]