Frontonasal dysplasia

Frontonasal dysplasia
Synonyms	median cleft face syndrome, frontonasal dysostosis, frontonasal malformation, Tessier cleft number 0/14
Classification and external resources
Specialty	medical genetics
ICD-10	Q75.8
ICD-9-CM	756.0
OMIM	136760
MeSH	C538065
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Frontonasal dysplasia (FND) is a congenital malformation of the midface. For the diagnosis of FND, a patient should present at least two of the following characteristics: hypertelorism (an increased distance between the eyes), a wide nasal root, vertical midline cleft of the nose and/or upper lip, cleft of the wings of the nose, malformed nasal tip, encephalocele (an opening of the skull with protrusion of the brain) or V-shaped hair pattern on the forehead. The cause of FND remains unknown. FND seems to be sporadic (random) and multiple environmental factors are suggested as possible causes for the syndrome. However, in some families multiple cases of FND were reported, which suggests a genetic cause of FND.

Midfacial malformations can be subdivided into two different groups. One group with hypertelorism, this includes FND. The other with hypotelorism (a decreased distance between the eyes), this includes holoprosencephaly (failure of development of the forebrain). In addition, a facial cleft can be classified using the Tessier classification. Each of the clefts is numbered from 0 to 14. The 15 different types of clefts are then subdivided into 4 groups, based on their anatomical position in the face: midline clefts, paramedian clefts, orbital clefts and lateral clefts. FND is a midline cleft, classified as Tessier 0/14.

Besides this, the additional anomalies seen in FND can be subdivided by region. None of these anomalies are specific for the syndrome of FND, but they do occur more often in patients with FND than in the population. The anomalies that may be present are:

The clefts of the face that are present in FND are vertical clefts. These can differ in severity. When they are less severe, they often present with hypertelorism and normal brain development. Mental retardation is more likely when the hypertelorism is more severe or when extracephalic anomalies occur.

There are multiple classification systems for FND. None of these classification systems have unraveled any genetic factors as the cause of FND. Yet, all of them are very valuable in determining the prognosis of an individual. In the subheadings below, the most common classifications will be explained.

This is a classification based on the embryological cause of FND.

This classification is based on the morphologic characteristics of FND, that describes a variety of phenotypes

Both of these classifications are further described in table 1. This table originates from the article ‘Acromelic frontonasal dysplasia: further delineation of a subtype with brain malformations and polydactyly (Toriello syndrome)', Verloes et al.

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