Clinical Description
Most individuals with a heterozygous pathogenic variant in ARID1B have some features consistent with Coffin-Siris syndrome.
Note: (1) The Coffin-Siris syndrome GeneReviews chapter includes information on individuals with CSS from a variety of genetic causes including ARID1B but is not specific to individuals with a pathogenic variant in ARID1B. (2) Approximately 1/2 to 2/3 of individuals with molecularly confirmed CSS have a pathogenic variant in ARID1B [van der Sluijs et al 2019]. More data are needed to determine which CSS features are found more or less frequently in individuals with a pathogenic variant in ARID1B.
To date, approximately 100 individuals who do not have the classic Coffin-Siris syndrome phenotype have been identified with a heterozygous pathogenic variant in ARID1B [Santen et al 2013, Santen et al 2014, Ben-Salem et al 2016, Mannino et al 2018, van der Sluijs et al 2019].
A comparison between individuals with a heterozygous pathogenic variant in ARID1B with an a priori clinical diagnosis of CSS and a group without the a priori clinical diagnosis suggests that apart from CSS-specific features (hypo/aplasia of the fifth digits or nails of the hands/feet, sparse scalp hair, coarse facial features, hypertrichosis) there are no major differences between the two groups [van der Sluijs et al 2019]. Therefore, the Authors treat them as a single entity, ARID1B-related disorder (ARID1B-RD).
Developmental delay (DD) and intellectual disability (ID). Intellectual disability ranges from profound to very mild, and intelligence quotients (IQs) in the normal range have been identified in some individuals with ARID1B-RD. Most affected individuals have developmental delay, with speech often more affected than motor development. An estimated 25% of affected individuals do not develop verbal language skills [van der Sluijs et al 2019].
Neurologic/epilepsy
Behavior problems. Individuals with ARID1B-RD appear to be at increased risk for a diagnosis of ADHD or autism, but the overall prevalence is not known, as many individuals now receiving the diagnosis at a younger age may not yet be old enough to evaluate for certain neurodevelopmental abnormalities. There does not appear to be an increased prevalence of self-harm, aggression, or sleep disturbances. Some behavior abnormalities may be exacerbated by an individual's degree of speech delay and difficulty with communication.
Growth. There are limited data regarding prenatal growth in individuals with ARID1B-RD. Postnatal growth data show the following:
Weight may be normal or below average but appears to be in proportion to other growth parameters.
The majority of affected individuals appear to have a length/height 0 to 2 SD below the mean; data are not sufficient to predict final adult height.
Bone age appears to be delayed in approximately 50% of individuals who have been evaluated.
Head circumference is normal in a majority of individuals with ARID1B-RD.
Gastrointestinal problems. Feeding difficulties are common and appear to approximate those seen in individuals with a diagnosis of CSS from a variety of genetic causes.
Individuals with feeding difficulties commencing around the time of birth appear to have more severe issues and tend to require a feeding tube of some type (nasogastric or gastrostomy tube).
In older children, milder feeding difficulties may occur, including oral aversion, particularly in those who required tube feeding as an infant or younger child.
Constipation and gastroesophageal reflux disease are also common and may approximate that seen in individuals with CSS or other genetic syndromes with varying degrees of neurologic impairment [
Mannino et al 2018].
Sensory impairment
Approximately 25%-30% of affected individuals have some
vision abnormality, although this frequency may not be significantly different from that of individuals with CSS from a variety of genetic causes [
Mannino et al 2018]. The most frequently reported abnormalities include myopia, strabismus, and astigmatism.
Similarly, 25%-40% of affected individuals have some degree of
hearing loss, the most common being congenital sensorineural hearing loss, although conductive hearing loss has also been reported [
Mannino et al 2018,
van der Sluijs et al 2019]. The range of severity of sensorineural hearing loss is not precisely known.
Neuroimaging. Of those individuals who have undergone brain imaging, approximately 30%-40% demonstrate brain anomalies. The most common abnormality is hypo- or aplasia of the corpus callosum [van der Sluijs et al 2019]. Delayed myelination or other white matter changes, colpocephaly, mega cisterna magna, and enlarged Virchow-Robin spaces are also seen. Additional brain abnormalities may be detected as more individuals undergo imaging.
Other associated features
Respiratory abnormalities. Laryngomalacia has been documented, although it does not appear to occur more frequently than in individuals with CSS due to a variety of genetic causes [
Mannino et al 2018,
van der Sluijs et al 2019]. Asthma and obstructive sleep apnea have also been reported but may approximate the frequency of the general population.
Genitourinary (GU) abnormalities. The most commonly reported GU abnormality appears to be cryptorchidism in males; structural renal abnormalities have been seen but the frequency of specific malformations is not known.
Musculoskeletal. Scoliosis is seen with greater frequency than in the general population and may be acquired as affected individuals age. Shortened fifth digits or hypoplastic nails in the hands or feet may also be seen, as these are classically associated with CSS.
Dysmorphic features. Affected individuals may have some features also seen in individuals with CSS from a variety of genetic causes, including sparse scalp hair, long eyelashes, hypertrichosis, and coarse facial features; more specifically, individuals may have thick alae nasi, a long philtrum, and a thick vermilion of the lower lip.
Prognosis. It is unknown if life span in individuals with ARID1B-RD is abnormal. One reported individual is alive at age 51 years [Santen, personal observation], and a woman age 60 years has also been reported [Määttänen et al 2018], demonstrating that survival into adulthood is possible. Since many adults with disabilities have not undergone advanced genetic testing, it is likely that adults with this condition are underrecognized and underreported.
Genotype-Phenotype Correlations
To date, only loss-of-function variants (e.g., nonsense, splice site, frameshift, whole-gene deletions) cause ARID1B-RD. Missense variants do not appear to be pathogenic in general; however, a single missense variant in a proband (who had agenesis of the corpus callosum [ACC]) and the proband's mother (who did not have ACC but had mild ID) was described as de novo in the mother [Mignot et al 2016].
There do not appear to be specific genotype-phenotype correlations among individuals with ARID1B-related disorder to distinguish individuals with ARID1B intellectual disability with or without nonspecific dysmorphic features (ARID1B-ID) from those with ARID1B Coffin-Siris syndrome (ARID1B-CSS).