Cri-du-chat syndrome was first described by Lejeune et al. (1963) as a hereditary congenital syndrome associated with deletion of part of the short arm of chromosome 5. The deletions can vary in size from extremely small and involving only band 5p15.2 to the entire short arm. Although the majority of deletions arise as new mutations, approximately 12% result from unbalanced segregation of translocations or recombination involving a pericentric inversion in one of the parents.

Pantothenate kinase-associated neurodegeneration (PKAN) is a type of neurodegeneration with brain iron accumulation (NBIA). The phenotypic spectrum of PKAN includes classic PKAN and atypical PKAN. Classic PKAN is characterized by early-childhood onset of progressive dystonia, dysarthria, rigidity, and choreoathetosis. Pigmentary retinal degeneration is common. Atypical PKAN is characterized by later onset (age >10 years), prominent speech defects, psychiatric disturbances, and more gradual progression of disease.

Urofacial syndrome (UFS) is characterized by prenatal or infantile onset of urinary bladder voiding dysfunction, abnormal facial movement with expression (resulting from abnormal co-contraction of the corners of the mouth and eyes), and often bowel dysfunction (constipation and/or encopresis). Bladder voiding dysfunction increases the risk for urinary incontinence, megacystis, vesicoureteric reflux, hydroureteronephrosis, urosepsis, and progressive renal impairment. In rare instances, an individual who has (a) a molecularly confirmed diagnosis and/or (b) an affected relative meeting clinical diagnostic criteria manifests only the characteristic facial features or only the urinary bladder voiding dysfunction (not both). Nocturnal lagophthalmos (incomplete closing of the eyes during sleep) appears to be a common and significant finding.

Familial paroxysmal nonkinesigenic dyskinesia (PNKD) is characterized by unilateral or bilateral involuntary movements. Attacks are typically precipitated by coffee, tea, or alcohol; they can also be triggered by excitement, stress, or fatigue, or can be spontaneous. Attacks involve dystonic posturing with choreic and ballistic movements, may be accompanied by a preceding aura, occur while the individual is awake, and are not associated with seizures. Attacks last minutes to hours and rarely occur more than once per day. Attack frequency, duration, severity, and combinations of symptoms vary within and among families. Age of onset is typically in childhood or early teens but can be as late as age 50 years.

Rubinstein-Taybi syndrome (RSTS) is characterized by distinctive facial features, broad and often angulated thumbs and halluces, short stature, and moderate-to-severe intellectual disability. The characteristic craniofacial features are downslanted palpebral fissures, low-hanging columella, high palate, grimacing smile, and talon cusps. Prenatal growth is often normal, then height, weight, and head circumference percentiles rapidly drop in the first few months of life. Short stature is typical in adulthood. Obesity may develop in childhood or adolescence. Average IQ ranges between 35 and 50; however, developmental outcome varies considerably. Some individuals with EP300-RSTS have normal intellect. Additional features include ocular abnormalities, hearing loss, respiratory difficulties, congenital heart defects, renal abnormalities, cryptorchidism, feeding problems, recurrent infections, and severe constipation.

Intellectual developmental disorder with paroxysmal dyskinesia or seizures (IDDPADS) is an autosomal recessive complex neurologic disorder characterized by global developmental delay with impaired intellectual development and language delay. In addition, most patients develop a paroxysmal hyperkinetic movement disorder in the first months or years of life manifest as sudden falls or backward propulsion, eye or head deviation, and dystonic limb posturing followed by chorea and dyskinetic movements. The episodes are pharmacoresistant to anticonvulsant medication. EEG may show interictal abnormalities, but are usually not consistent with epilepsy. However, some patients may also develop epileptic seizures or only have seizures without a movement disorder (summary by Doummar et al., 2020).