Common molecular categories such as deletions and UPDs exhibit significant differences in clinical features. Paternal absence is associated with significant nutritional problems, sleep disturbances, depigmentation, speech impairment, and other symptoms [17]. Conversely, cases of UPD are often associated with prolonged gestation, increased verbal IQ, psychosis, and autism [18]. However, a UPD patient is less likely to have her PWS facies and pigmentation. To date, no genetic mutation has been described as a contributor to the devolopment of the syndrome. In a previous study, our group proposed an individualized analysis of genes and their role in the devolopment of clinical phenotypes. As has been demonstrated in this paper, the extensive clinical spectrum and the absence of a genotype phenotype specific correlation suggest that the multiple genes associated with PWS have an additive deleterious effect when deficiently expressed. Nevertheless, the lack of expression of the SNORD116 gene cluster appear to be the best explanation for most of the PWS phenotype, although there is a need to investigate more of its mechanisms of action [13]. After that, the next step was to analyze if there was a genotype–phenotype correlation of our patients.

Clinical data from 45 PWS patients, mostly aged 1–28 years (mean 9 years), showed a frequency of 64.4% in deletion and 35.6% in UPD groups, slightly consistent with previous studies [7, 19]. Studies have also found an older maternal age within her UPD groups compared to deletions [4, 20, 21]. In particular, data on maternal age were not available in our study, however national statistics from DataSUS [22] show that between 2005 and 2020, maternal age increased annually in Brazil, especially in the 30–34 and 35–39 age groups, with increases of 28% and 62.6%, respectively. The higher frequency of UPD patients found in our study may be attributed, in part, to current trend of later pregnancies among women, which is a risk factor to the occurrence of UPD. In our cohort, we also conducted an analysis of the age at diagnostics, which ranged from 5 months to 23 years, with a median age of 1 year and 4 months, highlighting the crucial role of the reference laboratory in molecular diagnostics of PWS.

Regarding the possible influence of sex on patients with PWS, previous studies have shown discrepant results. Sanjeeva et al. [23] highlighted a higher prevalence of diagnoses in boys than in girls, while Gunay-Aygun et al. [24] reported a similar gender ratio. In our study, the gender ratio among PWS patients was approximately 1:1 (21 boys and 24 girls). Although our results do not manifest this difference between genders, certain specific signs, and symptoms of the syndrome, such as cryptorchidism, are more easily identifiable in boys. Establishing some level of complexity in the clinical diagnosis of these patients.

This study investigated the main clinical phenotypes in newborns with PWS, including severe neonatal hypotonia that improves with age (100%), almond-shaped eyes (86.6%), failure to thrive in childhood (82.2%), reduced fetal activity (80%), cryptorchidism (77.2%), and weak crying (62.2%). The results of WANG et al. [25] presented rates of hypotonia and weak crying higher than 95%, which is consistent with our data on hypotonia; however, the difference in results regarding weak crying may be explained by the fact that this clinical sign is subjectively judged by physicians.

Hypothalamic dysfunction underlies the major symptoms of patients with PWS [26, 27]. Symptoms of genital maldevelopment vary by gender, affecting the genitalia in men and the clitoris or genitalia in women. Male signs are evident at birth, whereas unlike male signs, female signs during the neonatal period can be obscured by obesity [28, 29]. In our study, 90.5% of 21 men had such symptoms, whereas only 29.1% of 24 women had such symptoms. Clinical observation bias could impact the analysis outcomes.

In this study, all cases of hypopigmentation were observed in patients with a deletion. However, this finding did not show a statistically significant difference in our analysis. We found a lower incidence of skin hypopigmentation (20.7%) in our study group compared to the 70–100% incidence of cutaneous hypopigmentation described in different studies [24, 30]. One possible explanation that should be investigated by us is the ethnic groups of the patients, as skin hypopigmentation is less easily identified among Caucasian individuals. The discrepancies can be attributed to (a) small sample sizes that are susceptible to selection bias or (b) the absence of a standardized clinical evaluation for skin hypopigmentation that is easily overlooked. Therefore, to determine if our results align with these studies, we need to increase the sample size, standardize the evaluation criteria, and conduct further research. The analysis of 54 cases of pediatric patients with PWS by Cassidy et al. [31] reported that the incidence rate of skin hypopigmentation in cases associated with deletion is much higher than that in UPD. Analyzing the structure of the genomic region of chromosome 15 associated with PWS, we observed the presence of the OCA2 gene associated with type 2 oculocutaneous albinism, tyrosinase-positive. This gene is within the different breakpoints that lead to the appearance of two different deletion sizes.

In the present study, it was not possible to identify patients with defects in the imprinting center. The use of MS-MLPA confirmed the diagnosis by MS-HRM and in some cases allowed the identification of some deletions in 58% of the patients. Due to a limitation of the technique, individuals where deletions were not identified (52%) were analyzed indirectly for UPD and directly for the imprinting center defect.

In summary, hypotonia, feeding difficulties, and underdeveloped genital are general clinical features of PWS. Hypopigmentation of the skin, poor development of sex glands, specific facial characteristics, GH deficiency, and other characteristics described in Table 1 did not show significant differences between deletion and UPD.

Sinnema et al. [32] reported that patients with PWS have higher rates of maladaptive behaviors compared to other syndromes with intellectual disability. Webb et al. [33] suggested that UPD cases have milder maladaptive behaviors compared to deletion cases but have a higher risk of autism spectrum disorders and psychosis.

In our study, myopia showed a significant difference between the groups (p < 0.05). Myopia, following the diagnostic criteria established by Holm et al. [2], is considered a minor criterion and is associated with deletion. One possible molecular explanation is the loss of the HERC2 gene. This gene belongs to the HERC gene family, which encodes a group of proteins that have various structural domains. All members have at least one copy of an N-terminal region showing homology to the cell cycle regulator RCC1, and a C-terminal HECT domain (homologous to the C-terminus of E6-AP) found in a series of ubiquitin protein ligase E3s. Genetic variations in this gene are associated with variability in skin, hair, and eye pigmentation. Several pseudogenes of this gene are located on chromosomes 15 and 16. This gene is also associated with the development of refractive abnormalities characterized by the ability to see near objects, which is associated with the phenotype of myopia [13].

Hypothalamic dysfunction is associated with clinical phenotypes such as hyperphagia and obesity in PWS due to hypometabolism. GH deficiency is common because GH affects IGF-I synthesis [34]. Regarding obstructive sleep apnea, a significant difference was observed, with a higher frequency in deletion cases than in UPD cases (p < 0.05). This condition may be associated with hypothalamic endocrine dysfunction that affects ventilatory control, leading to sleep-disordered breathing (SDB) [35]. From a molecular point of view, consultation with the Human Phenotype Ontology– HPO, using the key term obstructive sleep apnea, resulted in the association of genes and diseases present in the molecular region of PWS. For example, MAGEL2 deletion has been associated with Prader-Willi-like syndrome (ORPHA ID:398,069), including a UPD case (ORPHA ID:98,754) with a role for the SNRPN, OCA2, MAGEL2, and NDN genes. Deletion outcomes vary by type (ORPHA ID: 98,793, ORPHA ID: 177,901), including type 2 genes such as SNORD116-1, SNRPN, SNORD115-1, OCA2, MAGEL2, NDN, and their role in the development of apnea. and the desired phenotype are revealed.

Despite research on PWS, little is known about its cognitive aspects. Patients with PWS often have mild to moderate intellectual disability, poor short-term memory, improved visual motor skills, and spatial awareness [18, 36]. People with PWS are known to have a special talent for putting puzzles together. Compared to other individuals with some form of intellectual disability reported, the parents of these patients had a greater pleasure their children had with puzzle assembly. Holm et al. [2], based on clinical impressions, included the unusual ability with puzzles as a supportive criterion for the clinical diagnosis of PWS. This unusual ability with puzzles can be explained due to the visual-motor strengths that many of these patients present, as well as their obsessive-compulsive tendencies, need for order, accuracy, and for things to be “just right” [37]. Dykens [18] was the first to examine clinical impressions that people with PWS have puzzle and word search abilities. In our study, this significant difference was observed more frequently in deletion cases than in DUP cases (p < 0.05). Consistent with our results, Dykens showed that DUM patients performed worse than paternal deletion patients with puzzle assembly abilities. Due to the lack of studies regarding this finding, little is still known about how the lack of information derived from the paternal allele on chromosome 15 is associated with puzzle assembly abilities or why they vary among genetic subtypes.

HOLM and colleagues [2] developed a preclinical form for identifying individuals with suspected PWS, considering age, and creating a scoring system for diagnosis. Observing the results of these studies, we see that individuals present major within the criteria and that differences in favor of deletion, such as myopia and obstructive sleep apnea, were observed in minor characteristics. Additionally, in our population, we see these differences in supportive criteria, where in favor of deletion, the unusual ability with puzzles was a statistically significant finding. This makes sense since the molecular screening (MS-HRM) and clinical diagnoses were consistent.

The silencing of the MKRN3, NDN, and SNRPN-SNURF genes present on maternal chromosome 15 is associated with specific CpG island methylation in the promoter region of these genes [38], while their copies on the paternal allele are unmethylated and expressed. Based on the different methylation statuses of SNRPN-SNURF, combining MS-HRM and MS-MLPA techniques yields good results in diagnosis and genetic counseling. With the increasing availability and use of molecular diagnostics in clinical applications, an increasing number of patients with PWS are diagnosed at an early stage. Currently, there are few studies of PWS in large samples of newborns with Brazilian genetic constitution. This pilot study included 45 cases of PWS in Brazilians and is able to delineate the major clinical phenotypes of PWS carriers in Brazil.