The condition now known as Prader-Willi Syndrome (PWS) was first described by Langdon-Down in 1887, and the term Prader Labhart Willi Syndrome (later shortened to Prader-Willi Syndrome) was coined by Prader, Labhart and Willi in 1956 [1,2,3,4,5]. Currently, most authors agree that PWS is a complex multisystemic genetic disorder caused by the lack of expression of certain paternal genes located on the chromosome 15q11-q13 [4, 6, 7].
In 1981, Ledbetter demonstrated that most patients with PWS had an interstitial deletion of the proximal long arm of chromosome 15 at region q11–q13. Consequently PWS was described as one of the first examples of an error in genomic imprinting (GI) in humans. GI is a molecular process by which some genes are not expressed, due to the carrier parent. It is an epigenetic phenomenon in which the phenotype is modified depending on the mono-allele gene that is inherited from one of the parents. Therefore, the printing marks the genes in such a way that the origin of the two copies can be distinguished, with one parent’s copy being activated and the other’s copy silenced [8,9,10]. In the case of PWS, the process depends on the father, there is a fragment of the father’s chromosome 15q that is imprinted, that is to say, silenced, and so it is not expressed [9,10,11].
There are three genetic subtypes of PWS, whose common feature is the loss of expression of genes located at the 15q11-q13 locus. In descending order of frequency, these subtypes are: the deletion (DEL) of the 15q11-q13 region of paternal origin in about 65% of cases; maternal uniparental disomy (MUD) in about 30%, in which the individual presents two copies of the maternal chromosome 15; an imprinting center defect in less than 5% and rare cases of translocation involving the chromosome 15q11-q13 region [10]. This genetic anomaly leads to a pattern of physical characteristics with cognitive, neurological and endocrine abnormalities that change over the course of the patient’s life [12].
So PWS is a rare genetic disorder that can affect any race and sex [5, 8, 12,13,14] and has an estimated prevalence of 3.1: 100000 live newborns in Europe [15]. With regard to the patient’s eating habits, it is characterized by two stages. Newborns present severe hypotonia (Fig. 1), global developmental delay and lack of appetite. As a result they have difficulty gaining weight, and in most cases, feeding via nasogastric tube is necessary [4, 6, 13]. The second stage begins during early childhood; it is characterized by an eating disorder known as hyperphagia, which favors overweight and obesity [4, 6, 13, 16, 17].
In fact, PWS is the genetic syndrome most commonly associated with obesity, and its complications decrease life expectancy [4, 6, 9, 18, 19]. Apart from hyperphagia, patients also have a malfunctioning hypothalamus. The hypothalamus is a part of the brain that is responsible for integrating the nervous and endocrine systems which, together with the pituitary system, regulate aspects of growth, development, metabolism and homeostasis. Its main functions are the control of the autonomic nervous system by regulating visceral activity and the secretion of several glands; the production of hormones such as the growth hormone; the regulation of emotions, memory and behavior; the regulation of appetite; control of body temperature, and regulation of the heart rate and states of consciousness [20].
As a result, hypothalamic alterations can cause intellectual disability, behavioral problems, thermoregulatory dysfunction, a high pain threshold, respiratory sleep disorders, hypopigmentation, hypogonadism, pubertal delay and infertility, short stature, and small hands and feet (Fig. 2) [8, 21].
As for the facial phenotype, patients with PWS usually present a narrow forehead, elongated almond-shaped eyes with ascending oblique palpebral fissures, and a triangular mouth with commissures facing downwards and thin upper lip [1, 22,23,24].
The dietary problems associated with this general systemic condition increase the risk of oral pathology. It has been observed that patients with PWS are at greater risk of suffering oral diseases such as enamel hypoplasia, caries, tooth wear caused by attrition, erosion or abrasion, periodontal disease, delayed tooth eruption, candidiasis, oral lesions and decreased salivary flow (Fig. 3) [1, 18,19,20, 22, 24,25,26].
The Prader-Willi syndrome is characterized by low salivary quantity and quality due to atrophy of the salivary glands, which in turn is due to the low birth weight. Increased amounts of salivary ions and proteins make the saliva sticky, sparse and unable to perform its functions (Fig.4) [25, 27, 28]. The enamel hypoplasia may be caused by malnutrition and low birth weight, and is associated with the first phase of the syndrome [27, 29]. In addition, the combination of the lack of oral hygiene, reduced salivary flow and the preference for foods high in carbohydrates raises the risk of caries and gingivitis [18, 19, 24, 30]. These alterations in the oral cavity may be aggravated by the hypotonia which hinders suction, swallowing and chewing and makes the introduction of a soft diet mandatory [25].
The aim of this case-control study was to evaluate the oral conditions of children with Prader-Willi syndrome and to establish a prevention protocol for these patients.