What are the signs and symptoms of Prader-Willi syndrome? In infancy, Prader-Willi syndrome (PWS) is characterized by weak muscle tone (hypotonia), feeding difficulties, poor growth, and delayed development. In later infancy or early childhood, affected children develop an extreme appetite, which leads to overeating and obesity. Other signs and symptoms of PWS may include: mild to moderate intellectual disability sleep abnormalities unusually fair skin underdeveloped genitals delayed or incomplete puberty short stature strabismus scoliosis small hands and feet distinctive facial features such as a narrow forehead, almond-shaped eyes, and a triangular mouth Behavioral problems are common and often include temper tantrums, stubbornness, and obsessive-compulsive tendencies. The Human Phenotype Ontology provides the following list of signs and symptoms for Prader-Willi syndrome. If the information is available, the table below includes how often the symptom is seen in people with this condition. You can use the MedlinePlus Medical Dictionary to look up the definitions for these medical terms. Signs and Symptoms Approximate number of patients (when available) Delayed speech and language development 90% Failure to thrive in infancy 90% Generalized hypotonia 90% Growth hormone deficiency 90% Hypogonadotrophic hypogonadism 90% Infertility 90% Motor delay 90% Narrow palm 90% Obesity 90% Polyphagia 90% Poor suck 90% Short foot 90% Short palm 90% Short stature 90% Specific learning disability 90% Cryptorchidism 85% Attention deficit hyperactivity disorder 75% Scrotal hypoplasia 69% Adrenal insufficiency 60% Primary amenorrhea 56% Abnormality of chromosome segregation 50% Abnormality of dental enamel 50% Abnormality of the palate 50% Almond-shaped palpebral fissure 50% Behavioral abnormality 50% Brachydactyly syndrome 50% Clinodactyly of the 5th finger 50% Clitoral hypoplasia 50% Cognitive impairment 50% Cutaneous photosensitivity 50% Decreased muscle mass 50% Delayed puberty 50% Delayed skeletal maturation 50% Downturned corners of mouth 50% Glomerulopathy 50% Hypoplasia of penis 50% Hypoplasia of the ear cartilage 50% Hypoplastic labia minora 50% Incoordination 50% Intrauterine growth retardation 50% Kyphosis 50% Microcephaly 50% Micropenis 50% Muscular hypotonia 50% Narrow forehead 50% Narrow nasal bridge 50% Nasal speech 50% Recurrent respiratory infections 50% Scoliosis 50% Seizures 50% Single transverse palmar crease 50% Sleep apnea 50% Strabismus 50% Telecanthus 50% Type I diabetes mellitus 50% Hypopigmentation of hair 33% Hypopigmentation of the skin 33% Impaired pain sensation 33% Iris hypopigmentation 33% Oligomenorrhea 33% Ventriculomegaly 33% Type II diabetes mellitus 25% Autism 19% Psychosis 15% Hip dysplasia 10% Carious teeth 7.5% Esotropia 7.5% Frontal upsweep of hair 7.5% Myopia 7.5% Osteopenia 7.5% Osteoporosis 7.5% Poor fine motor coordination 7.5% Radial deviation of finger 7.5% Syndactyly 7.5% Temperature instability 7.5% Upslanted palpebral fissure 7.5% Precocious puberty 4% Abdominal obesity - Clinodactyly - Decreased fetal movement - Dolichocephaly - Generalized hypopigmentation - Hyperinsulinemia - Hypermetropia - Hypoventilation - Poor gross motor coordination - Sporadic - The Human Phenotype Ontology (HPO) has collected information on how often a sign or symptom occurs in a condition. Much of this information comes from Orphanet, a European rare disease database. The frequency of a sign or symptom is usually listed as a rough estimate of the percentage of patients who have that feature. The frequency may also be listed as a fraction. The first number of the fraction is how many people had the symptom, and the second number is the total number of people who were examined in one study. For example, a frequency of 25/25 means that in a study of 25 people all patients were found to have that symptom. Because these frequencies are based on a specific study, the fractions may be different if another group of patients are examined. Sometimes, no information on frequency is available. In these cases, the sign or symptom may be rare or common.