What is a cleft?
Cleft lip (cheiloschisis) and cleft palate (palatoschisis), which can also occur together as cleft lip and palate, are variations of a type of clefting congenital deformity caused by abnormal facial development during gestation. A cleft is a fissure or opening—a gap. It is the non-fusion of the body's natural structures that form before birth.
The face of a child begins to develop at approximately seven to nine weeks after conception.  The lip develops first at about seven weeks and the roof of the mouth, which is the hard and soft palate, at about the ninth week.  As the lip and the palate develop independently, it is possible to have either a cleft of the lip, a cleft of the palate or a combination of both.

Cleft lip
If the cleft does not affect the palate structure of the mouth it is referred to as cleft lip. Cleft lip is formed in the top of the lip as either a small gap or an indentation in the lip (partial or incomplete cleft) or it continues into the nose (complete cleft). It is due to the failure of fusion of the maxillary and medial nasal processes (formation of the primary palate).  The alveolar ridge (the portion of the bone where the teeth grow through the gum) may also be cleft.  The lip can be cleft to any degree on one side (unilateral) or on both sides (bilateral).

         

Unilateral incomplete                 Unilateral complete                   Bilateral complete

How common is cleft lip and/or palate?

In Australia approximately one in every 700 babies born will have some type of cleft.
In WA for the 2009 calendar year 70 babies were born with a cleft.

Cleft palate
Cleft palate is a condition in which the two plates of the skull that form the hard palate (roof of the mouth) are not completely joined. Palate cleft can occur as complete (soft and hard palate, possibly including a gap in the jaw) or incomplete (a 'hole' in the roof of the mouth, usually as a cleft soft palate). When cleft palate occurs, the uvula is usually split. It occurs due to the failure of fusion of the lateral palatine processes, the nasal septum, and/or the median palatine processes (formation of the secondary palate).
The hole in the roof of the mouth caused by a cleft connects the mouth directly to the nasal cavity.
Note: the next images show the roof of the mouth. The top shows the nose, the lips are colored pink. For clarity the images depict a toothless infant.

                  

Incomplete cleft palate          Unilateral complete lip and palate     Bilateral complete lip and palate

A direct result of an open connection between the oral cavity and nasal cavity is velopharyngeal inadequacy (VPI). Because of the gap, air leaks into the nasal cavity resulting in a hypernasal voice resonance and nasal emissions. Secondary effects of VPI include speech articulation errors (e.g., distortions, substitutions, and omissions) and compensatory misarticulations (e.g., glottal stops and posterior nasal fricatives). Possible treatment options include speech therapy, prosthetics, augmentation of the posterior pharyngeal wall, lengthening of the palate, and surgical procedures.
In a few instances a cleft will occur in the muscles of the soft palate only, leaving a veering of skin or “mucous membrane” still intact over the cleft.  This is called a submucous cleft and is not easily detected.

Combined cleft lip and palate
Any combination of the above clefts can occur together to produce a complete cleft of the lip and palate.

Pierre Robin Sequence
Some cleft babies have Pierre Robin Sequence which is characterized by an unusually small mandible (micrognathia),[1] posterior displacement or retraction of the tongue (glossoptosis), and upper airway obstruction. Incomplete closure of the roof of the mouth (cleft palate), is present in the majority of patients, and is commonly U-shaped.

Cause
The development of the face is coordinated by complex morphogenetic events and rapid proliferative expansion, and is thus highly susceptible to environmental and genetic factors, rationalising the high incidence of facial malformations. During the first six to eight weeks of pregnancy, the shape of the embryo's head is formed. Five primitive tissue lobes grow:
a) one from the top of the head down towards the future upper lip; (Frontonasal Prominence)
b-c) two from the cheeks, which meet the first lobe to form the upper lip; (Maxillar Prominence)
d-e) and just below, two additional lobes grow from each side, which form the chin and lower lip; (Mandibular Prominence)
If these tissues fail to meet, a gap appears where the tissues should have joined (fused). This may happen in any single joining site, or simultaneously in several or all of them. The resulting birth defect reflects the locations and severity of individual fusion failures (e.g., from a small lip or palate fissure up to a completely malformed face).
The upper lip is formed earlier than the palate, from the first three lobes named a to c above. Formation of the palate is the last step in joining the five embryonic facial lobes, and involves the back portions of the lobes b and c. These back portions are called palatal shelves, which grow towards each other until they fuse in the middle. This process is very vulnerable to multiple toxic substances, environmental pollutants, and nutritional imbalance. The biologic mechanisms of mutual recognition of the two cabinets, and the way they are glued together, are quite complex and obscure despite intensive scientific research.

Genetics
Genetic factors contributing to cleft lip and cleft palate formation have been identified for some syndromic cases, but knowledge about genetic factors that contribute to the more common isolated cases of cleft lip/palate is still patchy.

Many clefts run in families, even though in some cases there does not seem to be an identifiable syndrome present, possibly because of the current incomplete genetic understanding of midfacial development.

Environmental influences may also cause, or interact with genetics to produce, orofacial clefting. An example for how environmental factors might be linked to genetics comes from research on mutations in the gene PHF8 that cause cleft lip/palate (see above). It was found that PHF8 encodes for a histone lysine demethylase and is involved in epigenetic regulation. The catalytic activity of PHF8 depends on molecular oxygen a fact considered important with respect to reports on increased incidence of cleft lip/palate in mice that have been exposed to hypoxia early during pregnancy. In humans, fetal cleft lip and other congenital abnormalities have also been linked to maternal hypoxia, as caused by e.g. maternal smoking, maternal alcohol abuse or some forms of maternal hypertension treatment. Other environmental factors that have been studied include: seasonal causes (such as pesticide exposure); maternal diet and vitamin intake; retinoids - which are members of the vitamin A family; anticonvulsant drugs; alcohol; cigarette use; nitrate compounds; organic solvents; parental exposure to lead; and illegal drugs (cocaine, crack cocaine, heroin, etc.).

Current research continues to investigate the extent to which Folic acid can reduce the incidence of clefting.  Click here to read about the latest research on the link between folate in the diet and the occurence of isolated cleft lip.  The full article from the British Medical Journal can also be read by clicking here.
 

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