The most common symptoms of Nicolaides–Baraitser syndrome are mild to severe developmental delays with absent or limited speech, seizures, short stature, sparse hair, typical facial characteristics, brachydactyly, and prominent finger joints and broad distal phalanges.

Romano–Ward syndrome presents the following in an affected individual:

- Ventricular fibrillation

- Syncope

- Torsade de pointes

- Abnormality of ear

Romano–Ward syndrome is the major variant of "long QT syndrome". It is a condition that causes a disruption of the heart's normal rhythm. This disorder is a form of long QT syndrome, which is a heart condition that causes the cardiac muscle to take longer than usual to recharge between beats; if untreated, the irregular heartbeats can lead to fainting, seizures, or sudden death

The syndrome gets its name from the characteristic cry of affected infants, which is similar to that of a meowing kitten, due to problems with the larynx and nervous system. About 1/3 of children lose the cry by age of 2 years. Other symptoms of cri du chat syndrome may include:

- feeding problems because of difficulty in swallowing and sucking;

- low birth weight and poor growth;

- severe cognitive, speech, and motor delays;

- behavioral problems such as hyperactivity, aggression, outbursts, and repetitive movements;

- unusual facial features which may change over time;

- excessive drooling;

- small head and jaw;

- wide eyes;

- skin tags in front of eyes.

Other common findings include hypotonia, microcephaly, growth retardation, a round face with full cheeks, hypertelorism, epicanthal folds, down-slanting palpebral fissures, strabismus, flat nasal bridge, down-turned mouth, micrognathia, low-set ears, short fingers, single palmar creases, and cardiac defects (e.g., ventricular septal defect [VSD], atrial septal defect [ASD], patent ductus arteriosus [PDA], tetralogy of Fallot). Infertility is not associated with Cri du chat.

It has also been observed that people with the condition have difficulties communicating. While levels of proficiency can range from a few words to short sentences, it is often recommended by medical professionals for the child to undergo some sort of speech therapy/aid with the help of a professional.

Less frequently encountered findings include cleft lip and palate, preauricular tags and fistulas, thymic dysplasia, intestinal malrotation, megacolon, inguinal hernia, dislocated hips, cryptorchidism, hypospadias, rare renal malformations (e.g., horseshoe kidneys, renal ectopia or agenesis, hydronephrosis), clinodactyly of the fifth fingers, talipes equinovarus, pes planus, syndactyly of the second and third fingers and toes, oligosyndactyly, and hyperextensible joints. The syndrome may also include various dermatoglyphics, including transverse flexion creases, distal axial triradius, increased whorls and arches on digits, and a single palmar crease.

Late childhood and adolescence findings include significant intellectual disability, microcephaly, coarsening of facial features, prominent supraorbital ridges, deep-set eyes, hypoplastic nasal bridge, severe malocclusion, and scoliosis.

Affected females reach puberty, develop secondary sex characteristics, and menstruate at the usual time. The genital tract is usually normal in females except for a report of a bicornuate uterus. In males, testes are often small, but spermatogenesis is thought to be normal.

People with the combination of Duane anomaly and radial ray malformations may have a variety of other signs and symptoms. These features include:

- Unusually shaped ears

- Hearing loss

- Heart and kidney defects

- A distinctive facial appearance

- An inward- and downward-turning foot (a clubfoot)

- Fused vertebrae.

Mild prenatal growth retardation

Moderate postnatal growth retardation

Mild to severe developmental delay

Severely impaired speech

Seizures

Microcephaly

Sparse hair

Progressive skin wrinkling

Thick, anteverted alae nasi

Long and broad philtrum

Large mouth

Thin upper and thick lower vermilion

Progressive prominence of distal phalanges

Progressive prominence of inter-phalangeal joints

Short metacarpals–metatarsals

This is characterized by hand and arm abnormalities. The following are specific characteristics:

- Malformed or absent (aplasia) thumb

- A thumb that looks more like a finger

- Partial or complete absence of a radius

- Shortening and radial deviation of the forearms

- Triphalangeal thumb

- Duplication of the thumb (preaxial polydactyly)

Mal de debarquement (or mal de débarquement) syndrome (MdDS, or common name disembarkment syndrome) is a neurological condition usually occurring after a cruise, aircraft flight, or other sustained motion event. The phrase "mal de débarquement" is French for "sickness from disembarkation".

MdDS is typically diagnosed by a neurologist or an ear nose & throat specialist when a person reports a persistent rocking, swaying, or bobbing feeling (though they are not necessarily rocking). This usually follows a cruise or other motion experience. Because most vestibular testing proves to be negative, doctors may be baffled as they attempt to diagnose the syndrome. A major diagnostic indicator is that most patients feel better while driving or riding in a car, i.e.: while in passive motion. MdDS is unexplained by structural brain or inner ear pathology and most often corresponds with a motion trigger, although it can occur spontaneously. This differs from the very common condition of "land sickness" that most people feel for a short time after a motion event such as a boat cruise, aircraft ride, or even a treadmill routine which may only last minutes to a few hours. The syndrome has recently received increased attention due to the number of people presenting with the condition and more scientific research has commenced to determine what triggers MdDS and how to cure it.

The most common characteristics include a distinct craniofacial phenotype (microcephaly, micrognathia, short philtrum, prominent glabella, ocular hypertelorism, dysplastic ears and periauricular tags), growth restriction, intellectual disability, muscle hypotonia, seizures, and congenital heart defects. Less common characteristics include hypospadias, colobomata of the iris, renal anomalies, and deafness. Antibody deficiencies are also common, including common variable immunodeficiency and IgA deficiency. T-cell immunity is normal.

Aneuploidy is often fatal, but in this case there is "X-inactivation" where the effect of the additional gene dosage due to the presence of extra X chromosomes is greatly reduced.

Much like Down syndrome, the mental effects of 49,XXXXY syndrome vary. Impaired speech and behavioral problems are typical. Those with 49,XXXXY syndrome tend to exhibit infantile secondary sex characteristics with sterility in adulthood and have some skeletal anomalies. Skeletal anomalies include:

- Genu valgum

- Pes cavus

- Fifth finger clinodactyly

The effects also include:

- Cleft palate

- Club feet

- Respiratory conditions

- Short or/and broad neck

- Low birth weight

- Hyperextensible joints

- Short stature

- Narrow shoulders

- Coarse features in older age

- Hypertelorism

- Epicanthal folds

- Prognathism

- Gynecomastia (rare)

- Muscular hypotonia

- Hypoplastic genitalia

- Cryptorchidism

- Congenital heart defects

- A very round face in infancy

Symptoms most frequently reported include a persistent sensation of motion usually described as rocking, swaying, or bobbing, disequilibrium with difficulty maintaining balance; it is seldom accompanied by a true spinning vertigo. Chronically fatigued, sufferers can become fatigued quickly with minimal exertion and experience neck and back pain. Other common symptoms include difficulty concentrating or inability to multitask, visual intolerance of busy patterns, headaches and/or migraine headaches, and ear pain or fullness.

Fluctuations in weather, in particular barometric pressure, also affect suffers. Many have photo-sensitivity and find it more difficult to walk in the dark as well as other sensitivities to strong smells including chemical smells. Cognitive impairment ("brain fog") includes an inability to recall words, short term memory loss, an inability to multi-task, misspelling and mispronunciation of words. MdDS sufferers report they are unable to use a computer for any length of time due to the visual overstimulation, and some are even unable to watch television.

The condition may be masked by a return to motion such as in a car, train, plane, or boat; however, once the motion ceases, the symptoms rebound or return, often at much higher levels than when the journey first commenced. Symptoms can be increased by stress, lack of sleep, crowds, flickering lights, loud sounds, fast or sudden movements, enclosed areas or busy patterns.

MdDS sufferers can sleep up to 12 or more hours a day, depending on their symptom levels. Research reveals MdDS is not migraine related and many sufferers have never had migraine symptoms prior to the onset of the disorder. However, for some MdDS sufferers there maybe have been a correlation between migraine and some pathophysiological overlap or even some other precipitating illness.

The symptoms of MdDS may be extremely debilitating and fluctuate high and low on a daily basis; it greatly affects the working capacity of sufferers with many having to relinquish work; it also limits most other daily and social activities. Sufferers can have low quality of life in both the physical and emotional realms, comparable to people who have multiple sclerosis.

Following are the features and characteristics that help in spotting this disorder:

- Low birth weight (usually under 5 pounds/2.5 kilograms)

- Delayed growth and small stature

- Developmental delay

- Limb differences (missing limbs or portions of limbs)

- Small head size (microcephaly)

- Thick eyebrows, which typically meet at midline (synophrys)

- Long eyelashes

- Short upturned nose and thin downturned lips

- Long philtrum

- Excessive body hair

- Small hands and feet

- Small widely spaced teeth

- Low-set ears

- Hearing impairments

- Vision abnormalities (e.g., ptosis, nystagmus, high myopia, hypertropia)

- Partial joining of the second and third toes

- Incurved 5th fingers (clinodactyly)

- Gastroesophageal reflux

- Seizures

- Heart defects (e.g., pulmonary stenosis, VSD, ASD, coarctation of the aorta)

- Cleft palate

- Feeding problems

- Hypoplastic genitalia

Children with this syndrome are often found to have long eyelashes, bushy eyebrows and synophrys (joined eyebrows). Body hair can be excessive and affected individuals are often shorter than their immediate family members. They present a characteristic facial phenotype and is recognizable with the Facial Dysmorphology Novel Analysis (FDNA) technology

CdLS can give rise to its own array of complexities. Children with CdLS often suffer from gastrointestinal tract difficulties, particularly gastroesophageal reflux. Vomiting, intermittent poor appetite, constipation, diarrhea or gaseous distention are known to be a regularity in cases where the GI tract problems are acute. Symptoms may range from mild to severe.

CdLS may include behavior problems, including self-stimulation, aggression, self-injury or strong preference to a structured routine. Many children with CdLS exhibit autistic-like behaviors.

Behavior problems in CdLS are not inevitable. Many behavior issues associated with CdLS are reactive (i.e., something happens within the person's body or environment to bring on the behavior) and cyclical (comes and goes). Often, an underlying medical issue causes a change in behavior. Once the medical issue is treated, the behavior diminishes.

Cri du chat syndrome, also known as chromosome 5p deletion syndrome, 5p− syndrome (pronounced "Five P Minus") or Lejeune’s syndrome, is a rare genetic disorder due to chromosome deletion on chromosome 5. Its name is a French term ("cat-cry" or "call of the cat") referring to the characteristic cat-like cry of affected children. It was first described by Jérôme Lejeune in 1963. The condition affects an estimated 1 in 50,000 live births across all ethnicities and is more common in females by a 4:3 ratio.

It causes facial abnormalities, skeletal malformation and occasionally neural tube defects; the skeletal disfigurements resolve to a degree in the course of development.

Mutations in different parts of the gene may lead to deafness or Stickler syndrome type III (eye problems: myopia, retinal detachment and skeletal abnormalities).

Infants and children: Infants that are born with Weissenbacher-Zweymüller syndrome usually have short bones in their arms and legs. The thigh and upper arm bones are wider than usual resulting in a dumbbell-shape while the bones of the vertebrae may be abnormal. Typical abnormal facial features can be wide-set protruding eyes (hypertelorism), a small and upturned nose with a flat bridge, small jaw (micrognathia) and a cleft palate. Some infants have high-frequency hearing loss. Infants may also exhibit a psychomotor delay. After the period of growth deficiency the individual makes improvements in bone growth leading to a normal physical development around age 5 or 6.

Adults: Many with Weissenbacher-Zweymüller syndrome have a catch-up growth phase causing the adults to not be unusually short. Many adults still will have hearing loss and typical abnormal facial features of Weissenbacher-Zweymüller syndrome.

Revesz syndrome is a fatal disease that causes exudative retinopathy and bone marrow failure. Other symptoms include severe aplastic anemia, intrauterine growth retardation, fine sparse hair, fine reticulate skin pigmentation, ataxia due to cerebellar hypoplasia, and cerebral calcifications. Its effects are similar to that of Hoyeraal-Hreidarsson syndrome. It is a variant of dyskeratosis congenita.

UV-sensitive syndrome is a cutaneous condition inherited in an autosomal recessive fashion, characterized by photosensitivity and solar lentigines. Recent research identified that mutations of the KIAA1530 (UVSSA) gene as cause for the development of UV-sensitive syndrome. Furthermore, this protein was identified as a new player in the Transcription-coupled repair (TC-NER).

Drug-induced QT prolongation is seen with a QT interval above 0.45 ms on the ECG and is usually a result of treatment by anti-arrhythmic drugs, such as amiodarone and sotalol, or a number of other drugs that have been reported to cause this problem (e.g., cisapride). Some antipsychotic drugs, such as haloperidol and ziprasidone, have a prolonged QT interval as a rare side-effect. Antihistamines, erythromycin, and ciprofloxacin may also cause drug-induced LQT. Genetic mutations may make one more susceptible to drug-induced LQT. It is associated with hypokalaemia, hypocalcaemia and hypothermia and may lead to torsades de pointes.

List of drugs associated with prolonging the QT interval that may or may not have FDA warnings.

- Antiarrhythmic agents

- Type I

- Quinidine

- Disopyramide

- Procainamide

- Type III

- Sotalol

- Amiodarone

- Dofetilide

- Antibiotics

- Macrolides

- Erythromycin

- Clarithromycin

- Azithromycin

- Quinolones

- Levofloxacin

- Moxifloxacin

- Other

- Bedaquiline

- Delamanid

- Pentamidine

- Antifungals

- Fluconazole

- Ketoconazole

- Antihistamine

- Astemizole

- Hydroxyzine

- Mizolastine

- Terfenadine

- Antimalarials

- Chloroquine

- Halofantrine

- Antiretrovirals

- Lopinavir

- Ritonavir

- Saquinavir

- Chemotherapy

- Vandetanib

- Diuretics

- Furosemide

- Gastroprokinetic

- Cisapride

- Opioids

- Apomorphine

- Methadone

- Psychoactive drug

- Amitriptyline

- Asenapine

- Citalopram

- Cocaine

- Escitalopram

- Fluphenazine

- Haloperidol (IV higher risk than PO or IM)

- Iloperidone

- Lurasidone

- Olanzapine

- Paliperidone

- Pimozide

- Quetiapine

- Risperidone

- Thioridazine

- Ziprasidone

- Selective estrogen receptor modulators

- Tamoxifen

- Toremifene

Wolf–Hirschhorn syndrome (WHS), also known as chromosome deletion Dillan 4p syndrome, Pitt–Rogers–Danks syndrome (PRDS) or Pitt syndrome, was first described in 1961 by Americans Herbert L. Cooper and Kurt Hirschhorn and, thereafter, gained worldwide attention by publications by the German Ulrich Wolf, and Hirschhorn and their co-workers, specifically their articles in the German scientific magazine "Humangenetik". It is a characteristic phenotype resulting from a partial deletion of chromosomal material of the short arm of chromosome 4 (del(4p16.3)).

De Barsy syndrome is a rare autosomal recessive genetic disorder. Symptoms include cutis laxa (loose hanging skin) as well as other eye, musculoskeletal, and neurological abnormalities. It is usually progressive, manifesting side effects that can include clouded corneas, cataracts, short stature, dystonia, or progeria (premature aging).

It was first described in 1967 by De Barsy et al. and, as of 2011, there have been 27 cases reported worldwide. The genes that cause De Barsy syndrome have not been identified yet, although several studies have narrowed down the symptoms' cause. A study by Reversade et al. has shown that a mutation in PYCR1, the genetic sequence that codes for mitochondrial enzymes that break down proline, are prevalent in cases of autosomal recessive cutis laxa (ARCL), a condition very similar to De Barsy syndrome. A study by Leao-Teles et al. has shown that De Barsy syndrome may be related to mutations in ATP6V0A2 gene, known as ATP6V0A2-CDG by the new naming system.

Alternative names for De Barsy syndrome include corneal clouding-cutis laxa-mental retardation, cutis laxa-growth deficiency syndrome, De Barsy–Moens–Diercks syndrome, and progeroid syndrome of De Barsy.

Jervell and Lange-Nielsen syndrome (JLNS) is a type of long QT syndrome associated with severe, bilateral sensorineural hearing loss. Long QT syndrome causes the cardiac muscle to take longer than usual to recharge between beats. If untreated, the irregular heartbeats, called arrhythmias, can lead to fainting, seizures, or sudden death. It was first described by Anton Jervell and Fred Lange-Nielsen in 1957.

Many people with long QT syndrome have no signs or symptoms.

Some people may experience the following symptoms:

- Fainting (or syncope). This may occur when the patient is emotionally or physically stressed. It is unusual in QT syndrome to have any signs before the person actually faints.

- Seizures

- Sudden death. If there is sudden death, and doctors suspect long QT syndrome as the cause, they may recommend that the family members of the deceased get tested for the disease.

ATR-16 syndrome affects the blood, development, and brain; symptoms vary based on the specific genes deleted on chromosome 16. Because it is so rare, it is difficult to determine the "core" symptoms of the disease. People with ATR-16 have alpha-thalassemia, a blood disorder where there is less normal hemoglobin in the blood than there should be, and the red blood cells are smaller than they should be (microcytic anemia). Affected children have various characteristic physical features, including clubfoot, "locked" little fingers, microcephaly (small head), hypertelorism (widely spaced eyes), broad, prominent nose bridge, downward-slanted palpebral fissures, small ears, retrognathia, and short neck. Children with ATR-16 syndrome also have mild to moderate intellectual disabilities, developmental delays/growth delays, and speech delays. Some children with ATR-16 have seizures, cryptorchidism (undescended testes), or hypospadias.

A case was described in 1957 by Michail, Matsoukas and Theodorou. In 1963, Jack Herbert Rubinstein (1925–2006) and Hooshang Taybi (1919–2006) described a larger series of cases.

Typical features of the disorder include:

- Broad thumbs and broad first toes and clinodactyly of the 5th finger

- Mental disability

- Small height, low bone growth, small head

- Cryptorchidism in males

- Unusual facies involving the eyes, nose, and palate

- Anesthesia may be dangerous in these patients: "According to the medical literature, in some cases, individuals with Rubinstein–Taybi syndrome may have complications (e.g., respiratory distress and/or irregular heart beats [cardiac arrythmias]) associated with a certain muscle relaxant (succinylcholine) and certain anesthesia. Any situations requiring the administration of anesthesia or succinylcholine (e.g., surgical procedures) should be closely monitored by skilled professionals (Anesthesiologists)." Primary literature suggests the children may have a higher rate of cardiac physical and conduction abnormalities which may cause unexpected results with cardioactive medications. A further editorial reply in the British Journal of Anaesthesia discusses changes in the face and airway structure making it more difficult to secure the airway under anaesthesia, however, complications appeared in a minority of cases, and routine methods of airway control in the operating room appears to be successful. They recommended close individual evaluation of Rubinstein–Taybi patients for anaesthetic plans.

A 2009 study found that children with RTS were more likely to be overweight and to have a short attention span, motor stereotypies, and poor coordination, and hypothesized that the identified CREBBP gene impaired motor skills learning. Other research has shown a link with long-term memory (LTM) deficit. See also Epigenetics in learning and memory.

49,XXXXY syndrome is an extremely rare aneuploidic sex chromosomal abnormality. It occurs in approximately 1 out of 85,000 to 100,000 males.

Langer mesomelic dysplasia (LMD) is a rare congenital disorder characterized by an altered bone formation that causes a severe short and disproportionate stature.