The most common symptoms of Williams syndrome are heart defects and unusual facial features. Other symptoms include failure to gain weight appropriately in infancy (failure to thrive) and low muscle tone. Individuals with Williams syndrome tend to have widely spaced teeth, a long philtrum, and a flattened nasal bridge.

Most individuals with Williams syndrome are highly verbal relative to their IQ, and are overly sociable, having what has been described as a "cocktail party" type personality. Individuals with WS hyperfocus on the eyes of others in social engagements.

One of the most prominent and visible symptoms of Nevo Syndrome is the prenatal overgrowth, which continues into the infant and toddler stage. This excessive weight gain can be attributed to the low concentrations of growth hormone and insulin growth factor that are normally present to regulate weight gain. Other common symptoms associated with Nevo Syndrome are the outward wrist-drop, edema in hands and feet, undescended testes, low-set ears, hypotonia, the presence of low muscle tone in children, and long tapered fingers, and a highly arched palate.

The following is a list of symptoms that have been associated with Roberts syndrome:

- Bilateral Symmetric Tetraphocomelia- a birth defect in which the hands and feet are attached to shortened arms and legs

- Prenatal Growth Retardation

- Hypomelia (Hypoplasia)- the incomplete development of a tissue or organ; less drastic than aplasia, which is no development at all

- Oligodactyly- fewer than normal number of fingers or toes

- Thumb Aplasia- the absence of a thumb

- Syndactyly- condition in which two or more fingers (or toes) are joined together; the joining can involve the bones or just the skin between the fingers

- Clinodactyly- curving of the fifth finger (little finger) towards the fourth finger (ring finger) due to the underdevelopment of the middle bone in the fifth finger

- Elbow/Knee Flexion Contractures- an inability to fully straighten the arm or leg

- Cleft Lip- the presence of one or two vertical fissures in the upper lip; can be on one side (unilateral) or on both sides (bilateral)

- Cleft Palate- opening in the roof of the mouth

- Premaxillary Protrusion- upper part of the mouth sticks out farther than the lower part of the mouth

- Micrognathia- small chin

- Microbrachycephaly- smaller than normal head size

- Malar Hypoplasia- underdevelopment of the cheek bones

- Downslanting Palpebral Fissures- the outer corners of the eyes point downwards

- Ocular Hypertelorism- unusually wide-set eyes

- Exophthalmos- a protruding eyeball

- Corneal Clouding- clouding of the front-most part of the eye

- Hypoplastic Nasal Alae- narrowing of the nostrils that can decrease the width of the nasal base

- Beaked Nose- a nose with a prominent bridge that gives it the appearance of being curved

- Ear Malformations

- Intellectual disability

- Encephalocele (only in severe cases)- rare defect of the neural tube characterized by sac-like protrusions of the brain

Mortality is high among those severely affected by Roberts syndrome; however, mildly affected individuals may survive to adulthood

Most people with this condition have extra fingers and/or toes (polydactyly), and the skin between some fingers or toes may be fused (cutaneous syndactyly). An abnormal growth in the brain called a hypothalamic hamartoma is characteristic of this disorder. In many cases, these growths do not cause any medical problems; however, some hypothalamic hamartomas lead to seizures or hormone abnormalities that can be life-threatening in infancy. Other features of Pallister–Hall syndrome include a malformation of the airway called a bifid epiglottis, laryngeal cleft, an obstruction of the anal opening (imperforate anus), and kidney abnormalities. Although the signs and symptoms of this disorder vary from mild to severe, only a small percentage of affected people have serious complications.

The syndrome is a rare clinical disorder.

- Physical

- Overgrowth

- Accelerated skeletal maturation

- Dysmorphic facial features

- Prominent eyes

- Bluish sclerae

- Coarse eyebrows

- Upturned nose

- Radiologic examination

- Accelerated osseous maturation

- Phalangeal abnormalities

- Tubular thinning of the long bones

- Skull abnormalities

- Mental

- Often associated with intellectual disability (of variable degree)

Little is known about the natural history of Roberts syndrome due to its wide clinical variability. The prognosis of the disease depends on the malformations, as the severity of the malformations correlates with survival. The cause of death for most fatalities of Roberts syndrome have not been reported; however, five deaths were reportedly due to infection.

The following are observations that have been made in individuals with cytogenetic findings of PCS/HR or ESCO2 mutations:

- The symptom of prenatal growth retardation is the most common finding and can be moderate to severe. Postnatal growth retardation can also be moderate to severe and correlates with the degree of severity of limb and craniofacial malformations.

- In limb malformations, the upper limbs are typically more severely affected than the lower limbs. There have been many cases of only upper limb malformation.

- In hand malformations, the thumb is most often affected, followed by the fifth finger (the little finger). In severe cases, the patient may only have three fingers and in rare cases only one.

- In craniofacial malformations, mildly affected individuals will have no abnormalities of the palate. The most severely affected will have a fronto-ethmoid-nasal-maxillary encephalocele.

- The severity of limb malformations and craniofacial malformations is correlated.

- Other abnormalities can occur in different parts of the body, including:

- Heart- atrial septal defects, ventricular septal defects, patent ductus arteriosus

- Kidneys- polycystic kidney, horseshoe kidney

- Male Genitals- enlarged penis, cryptorchidism

- Female Genitals- enlarged clitoris

- Hair- sparse, silvery-blonde scalp hair

- Cranial Nerve Paralysis, Moyamoya disease, Stroke, Intellectual disability

The earliest observable symptoms of Williams syndrome include low birth weight, failure to thrive, trouble breastfeeding, nocturnal irritability and gastroesophageal reflux. Facial dysmorphies thought to be characteristic of the syndrome are also present early in development, as is heart murmur. Research on the development of the syndrome suggest that congenital heart disease is typically present at an early age, often at the infant's first pediatric appointment. Heart problems in infancy often lead to the initial diagnosis of Williams syndrome.

Developmental delays are present in most cases of Williams syndrome, and include delay of language abilities and delayed motor skill development. Individuals with Williams syndrome develop language abilities quite late relative to other children, with the child's first word often occurring as late as three years of age. Language abilities are often observed to be deficient until adolescence, in terms of semantics, morphology, and phonology, though not in vocabulary.

Williams syndrome is also marked by a delay in development of motor skills. Infants with Williams develop the ability to lift their heads and sit without support months later than typically developing children. These delays continue into childhood, where patients with Williams syndrome are delayed in learning to walk. In young children, the observed motor delay is around five to six months, though some research suggests that children with Williams syndrome have a delay in development that becomes more extreme with age. Children with motor delays as a result of Williams syndrome are particularly behind in development of coordination, fine motor skills such as writing and drawing, response time, and strength and dexterity of the arms. Impaired motor ability persists (and possibly worsens) as children with Williams syndrome reach adolescence.

Adults and adolescents with Williams syndrome typically achieve a below-average height and weight, compared with non-affected populations. As individuals with Williams syndrome age, they frequently develop joint limitations and hypertonia, or abnormally increased muscle tone. Hypertension, gastrointestinal problems, and genitourinary symptoms often persist into adulthood, as well as cardiovascular problems. Adults with Williams syndrome are typically limited in their ability to live independently or work in competitive employment settings, but this developmental impairment is attributed more to psychological symptoms than physiological problems.

As noted above, the hypothalamic hamartoma can cause seizures.

The most common types of seizures that occur are known as gelastic epilepsy.

The term "gelastic" originates from the Greek word ""gelos" which means "laughter". Seizures may begin at any age but usually before three or four years of age. The seizures usually start with laughter and the laughter is often described as being "hollow" or "empty" and not very pleasant. The laughter occurs suddenly, comes on for no obvious reason and is usually completely out of place. The most common areas of the brain which give rise to gelastic seizures are the hypothalamus (a small but extremely important structure deep in the centre of the brain), the temporal lobes and the frontal lobes. If the child has gelastic seizures and precocious puberty, then it is likely that the child will be found to have a hypothalamic hamartoma (a hamartoma in the hypothalamus part of the brain).

Nevo Syndrome is a rare autosomal recessive disorder that usually begins during the later stages of pregnancy. Nevo Syndrome is caused by a NSD1 deletion, which encodes for methyltransferase involved with chromatin regulation. The exact mechanism as to how the chromatin is changed is unknown and still being studied. Nevo Syndrome is an example of one of about twelve overgrowth syndromes known today. Overgrowth syndromes are characterized with children experiencing a significant overgrowth during pregnancy and also excessive postnatal growth. Studies concerning Nevo Syndrome have shown a similar relation to Ehlers-Danlos syndrome, a connective tissue disorder. Nevo Syndrome is associated with kyphosis, an abnormal increased forward rounding of the spine, joint laxity, postpartum overgrowth, a highly arched palate, undescended testes in males, low-set ears, increased head circumference, among other symptoms.

Children are most commonly identified with Aicardi syndrome before the age of five months. A significant number of girls are products of normal births and seem to be developing normally until around the age of three months, when they begin to have infantile spasms. The onset of infantile spasms at this age is due to closure of the final neural synapses in the brain, a stage of normal brain development. A number of tumors have been reported in association with Aicardi syndrome: choroid plexus papilloma (the most common), medulloblastoma, gastric hyperplastic polyps, rectal polyps, soft palate benign teratoma, hepatoblastoma, parapharyngeal embryonal cell cancer, limb angiosarcoma and scalp lipoma.

Although genetic testing positively identifies nearly two thirds of children with CHARGE syndrome, diagnosis is still largely clinical. The following signs were originally identified in children with this syndrome, but are no longer used in to make the diagnosis alone.

- C - Coloboma of the eye, central nervous system anomalies

- H - Heart defects

- A - Atresia of the choanae

- R - Retardation of growth and/or development

- G - Genital and/or urinary defects (Hypogonadism, undescended testicles, besides hypospadias.)

- E - Ear anomalies and/or deafness and abnormally bowl-shaped and concave ears, known as "lop ears".

The diagnosis of CHARGE syndrome is often difficult, because it is rare. The syndrome spans many disciplines, and as such, can be diagnosed by a pediatrician, oral and maxillofacial surgeon, ENT specialist, ophthalmologist, audiologist, endocrinologist, cardiologist, urologist, developmental specialist, radiologist, geneticist, physiotherapist, occupational therapist, speech therapist, or orthopedic specialist.

Aicardi syndrome is typically characterized by the following triad of features - however, one of the "classic" features being missing does not preclude a diagnosis of Aicardi Syndrome, if other supporting features are present.

1. Partial or complete absence of the corpus callosum in the brain (agenesis of the corpus callosum);

2. Eye abnormalities known as "lacunae" of the retina that are quite specific to this disorder; [optic nerve coloboma]]; and

3. The development in infancy of seizures that are called infantile spasms.

Other types of defects of the brain such as microcephaly, polymicrogyria, porencephalic cysts and enlarged cerebral ventricles due to hydrocephalus are also common in Aicardi syndrome.

The hearing loss associated with Stickler syndrome can be progressive and usually involves the high frequencies. Sensorineural hearing loss has been reported in as many as 100% and as low as 20% of affected individuals. A conductive loss due to otitis can magnify an existing sensorineural loss and is a frequent problem for children with Stickler or Marshall Syndrome.

Marshall-Smith Syndrome, discovered in 1971 (Marshall, Graham, Scott, Boner, & Smith), is characterized by unusual accelerated skeletal maturation (usually starting before birth) and symptoms like conspicuous physical characteristics, respiratory difficulties, and mental retardation. Cases described in the literature show a clinical variability regarding related symptoms. For instance, respiratory difficulties are ranging from absent to severe difficulties.

The Kocher–Debré–Semelaigne syndrome is hypothyroidism in infancy or childhood characterised by lower extremity or generalized muscular hypertrophy, myxoedema, short stature and cretinism. The absence of painful spasms and pseudomyotonia differentiates this syndrome from its adult form, which is Hoffmann syndrome.

The syndrome is named after Emil Theodor Kocher, Robert Debré and Georges Semelaigne.

Also known as Debre–Semelaigne syndrome or cretinism-muscular hypertrophy, hypothyroid myopathy, hypothyroidism-large muscle syndrome, hypothyreotic muscular hypertrophy in children, infantile myxoedema-muscular hypertrophy, myopathy-myxoedema syndrome, myxoedema-muscular hypertrophy syndrome, myxoedema-myotonic dystrophy syndrome.

Kocher-Debre-Semelaigne syndrome gives infant a Hercules appearance.

The most severe problem associated with Stickler syndrome is Pierre Robin syndrome. This refers to a cleft palate resulting from a very small lower jaw. During early fetal life, the roof of the mouth is normally open and the sides of the palate have to come together to close. If the jaw is too small, there is not enough room for the tongue which is then pushed up and gets in the way of the closing palate. Sometimes the chin is so small the baby has problems with eating and breathing if the tongue blocks the back of the throat. Cleft palate is found less frequently in Marshall Syndrome than in Stickler syndrome but still more frequently than in the general population.

The facial features of Marshall Syndrome include a flat midface, the appearance of large eyes, short upturned nose, and a round face. The facial features of Stickler syndrome are less prominent but include a rather long flat face, and depressed nasal bridge.

The classical triad of symptoms that defines 3C syndrome includes certain heart defects, hypoplasia (underdevelopment) of the cerebellum, and cranial dysmorphisms, which can take various forms. The heart defects and cranial dysmorphisms are heterogeneous in individuals who are all classed as having Ritscher-Schinzel syndrome.

Heart defects commonly seen with Ritscher-Schinzel syndrome are associated with the endocardial cushion and are the most important factor in determining a diagnosis. The mitral valve and tricuspid valve of the heart can be malformed, the atrioventricular canal can be complete instead of developing into the interatrial septum and interventricular septum, and conotruncal heart defects, which include tetralogy of Fallot, double outlet right ventricle, transposition of the great vessels, and hypoplastic left heart syndrome. Aortic stenosis and pulmonary stenosis have also been associated with 3C syndrome.

The cranial dysmorphisms associated with 3C syndrome are heterogeneous and include a degree of macrocephaly, a large anterior fontanel, a particularly prominent occiput and forehead, ocular hypertelorism (wide-set eyes), slanted palpebral fissures, cleft palate, a depressed nasal bridge, cleft palate with associated bifid uvula, low-set ears, micrognathia (an abnormally small jaw), brachycephaly (flattened head), and ocular coloboma. Low-set ears are the most common cranial dysmorphism seen in 3C syndrome, and ocular coloboma is the least common of the non-concurrent symptoms (cleft lip co-occurring with cleft palate is the least common).

Cranial dysplasias associated with 3C syndrome are also reflected in the brain. Besides the cerebellar hypoplasia, cysts are commonly found in the posterior cranial fossa, the ventricles and the cisterna magna are dilated/enlarged, and Dandy-Walker malformation is present. These are reflected in the developmental delays typical of the disease. 75% of children with 3C syndrome have Dandy-Walker malformation and hydrocephalus.

Signs and symptoms in other body systems are also associated with 3C syndrome. In the skeletal system, ribs may be absent, and hemivertebrae, syndactyly (fusion of fingers together), and clinodactyly (curvature of the fifth finger) may be present. In the GI and genitourinary systems, anal atresia, hypospadia (misplaced urethra), and hydronephrosis may exist. Adrenal hypoplasia and growth hormone deficiency are associated endocrine consequences of Ritscher-Schinzel syndrome. Some immunodeficiency has also been reported in connection with 3C syndrome.

Many children with the disorder die as infants due to severe congenital heart disease. The proband of Ritscher and Schinzel's original study was still alive at the age of 21.

A fetus with 3C syndrome may have an umbilical cord with one umbilical artery instead of two.

It can be detected by the naked eye as well as dental or skull X-Ray testing.

Theoretically, a mutation in any of the may cause disease, but below are some notable ones, with short description of symptoms:

- Adrenoleukodystrophy; leads to progressive brain damage, failure of the adrenal glands and eventually death.

- Alport syndrome; glomerulonephritis, endstage kidney disease, and hearing loss.

- Androgen insensitivity syndrome; variable degrees of undervirilization and/or infertility in XY persons of either gender

- Barth syndrome; metabolism distortion, delayed motor skills, stamina deficiency, hypotonia, chronic fatigue, delayed growth, cardiomyopathy, and compromised immune system.

- Blue cone monochromacy; low vision acuity, color blindness, photophobia, infantile nystagmus.

- Centronuclear myopathy; where cell nuclei are abnormally located in skeletal muscle cells. In CNM the nuclei are located at a position in the center of the cell, instead of their normal location at the periphery.

- Charcot–Marie–Tooth disease (CMTX2-3); disorder of nerves (neuropathy) that is characterized by loss of muscle tissue and touch sensation, predominantly in the feet and legs but also in the hands and arms in the advanced stages of disease.

- Coffin–Lowry syndrome; severe mental retardation sometimes associated with abnormalities of growth, cardiac abnormalities, kyphoscoliosis as well as auditory and visual abnormalities.

- Fabry disease; A lysosomal storage disease causing anhidrosis, fatigue, angiokeratomas, burning extremity pain and ocular involvement.

- Hunter's Syndrome; potentially causing hearing loss, thickening of the heart valves leading to a decline in cardiac function, obstructive airway disease, sleep apnea, and enlargement of the liver and spleen.

- Hypohidrotic ectodermal dysplasia, presenting with hypohidrosis, hypotrichosis, hypodontia

- Kabuki syndrome; multiple congenital anomalies and mental retardation.

- Spinal and bulbar muscular atrophy; muscle cramps and progressive weakness

- Lesch-Nyhan syndrome; neurologic dysfunction, cognitive and behavioral disturbances including self-mutilation, and uric acid overproduction (hyperuricemia)

- Lowe Syndrome; hydrophthalmia, cataracts, intellectual disabilities, aminoaciduria, reduced renal ammonia production and vitamin D-resistant rickets

- Menkes disease; sparse and coarse hair, growth failure, and deterioration of the nervous system

- Nasodigitoacoustic syndrome; mishaped nose, brachydactyly of the distal phalanges, sensorineural deafness

- Nonsyndromic deafness; hearing loss

- Norrie disease; cataracts, leukocoria along with other developmental issues in the eye

- Occipital horn syndrome; deformations in the skeleton

- Ocular albinism; lack of pigmentation in the eye

- Ornithine transcarbamylase deficiency; developmental delay and mental retardation. Progressive liver damage, skin lesions, and brittle hair may also be seen

- Siderius X-linked mental retardation syndrome; cleft lip and palate with mental retardation and facial dysmorphism, caused by mutations in the histone demethylase PHF8

- Simpson-Golabi-Behmel syndrome; coarse faces with protruding jaw and tongue, widened nasal bridge, and upturned nasal tip

- Spinal muscular atrophy caused by UBE1 gene mutation; weakness due to loss of the motor neurons of the spinal cord and brainstem

- Wiskott-Aldrich syndrome; eczema, thrombocytopenia, immune deficiency, and bloody diarrhea

- X-linked Severe Combined Immunodeficiency (SCID); infections, usually causing death in the first years of life

- X-linked sideroblastic anemia; skin paleness, fatigue, dizziness and enlarged spleen and liver.

Perlman syndrome shares clinical overlaps with other overgrowth disorders, with similarities to Beckwith–Wiedemann syndrome and Simpson-Golabi-Behmel syndrome having been particularly emphasized in scientific study. Similarities with Beckwith-Wiedemann syndrome include polyhydramnios, macrosomia, nephromegaly and hypoglycaemia. It is the distinctive facial dysmorphology of Perlman, including deep-set eyes, depressed nasal bridge, everted upper lip, and macrocephaly which allows the two conditions to be distinguished from one another. Diagnosis of Perlman syndrome also overlaps with other disorders associated with Wilms tumor, namely, Sotos syndrome and Weaver syndrome.

Psychiatric syndromes often called "psychopathological syndromes" (psychopathology is a psychic dysfunction occurring in mental disorder, also it's the study of the origin, diagnosis, development, and treatment of mental disorders).

In Russia those psychopathological syndromes are used in modern clinical practice and described in psychiatric literature in the details: asthenic syndrome, obsessive syndrome, emotional syndromes (for example, manic syndrome, depressive syndrome), Cotard's syndrome, catatonic syndrome, hebephrenic syndrome, delusional and hallucinatory syndromes (for example, paranoid syndrome, paranoid-hallucinatory syndrome, Kandinsky-Clérambault's syndrome also known as syndrome of psychic automatism, hallucinosis), paraphrenic syndrome, psychopathic syndromes (includes all personality disorders), clouding of consciousness syndromes (for example, twilight clouding of consciousness, amential syndrome also known as amentia, delirious syndrome, stunned consciousness syndrome, oneiroid syndrome), hysteric syndrome, neurotic syndrome, Korsakoff's syndrome, hypochondriacal syndrome, paranoiac syndrome, senestopathic syndrome, encephalopathic syndrome.

There are some examples of the psychopathological syndromes used in modern Germany: psychoorganic syndrome, depressive syndrome, paranoid-hallucinatory syndrome, obsessive-compulsive syndrome, autonomic syndrome, hostility syndrome, manic syndrome, apathy syndrome.

Also well known Münchausen syndrom, Ganser syndrome, neuroleptic-induced deficit syndrome, olfactory reference syndrome.

Pashayan syndrome also known as Pashayan–Prozansky Syndrome, and blepharo-naso-facial syndrome is a rare syndrome. Facial abnormalities characterise this syndrome as well as malformation of extremities. Specific characteristics would be a bulky, flattened nose, where the face has a mask like appearance and the ears are also malformed.

A subset of Pashayan syndrome has also been described, known as "cerebrofacioarticular syndrome", "Van Maldergem syndrome'" or "Van Maldergem–Wetzburger–Verloes syndrome". Similar symptoms are noted in these cases as in Pashayan syndrome.

There is an overlap in symptoms between 3C syndrome and Joubert syndrome. Joubert syndrome often manifests with similar cerebellar hypoplasia and its sequelae, including hyperpnea, ataxia, changes in eye movement, and cleft lip and palate. Occasionally, Joubert syndrome will include heart malformations. Brachmann-de Lange syndrome must also be differentiated from 3C syndrome. It presents with similar craniofacial and heart abnormalities and can include Dandy-Walker phenotype, making it difficult to distinguish. Dandy-Walker malformation is also occasionally seen in Ellis-van Creveld syndrome, which is characterized by heart defects and malformed alveolar ridge. Many disorders include the Dandy-Walker phenotype and thus it is not pathognomonic for 3C syndrome.

CHARGE syndrome can also be misdiagnosed. This is because both CHARGE syndrome and 3C syndrome share symptoms of ocular colobomas, cardiac defects, growth retardation, and minor facial abnormalities.

Coffin-Siris syndrome presents with fifth-finger deformities and congenital heart defects. It is distinguished from 3C syndrome by differences in facial dysmorphisms.

Low-set ears are ears with depressed positioning of the pinna two or more standard deviations below the population average.

It can be associated with conditions such as:

- Down's syndrome

- Turner Syndrome

- Noonan syndrome

- Patau syndrome

- DiGeorge syndrome

- Cri du chat syndrome

- Edwards syndrome

- Fragile X syndrome

It is usually bilateral, but can be unilateral in Goldenhar syndrome.