Clinical Description
GNAI1-related neurodevelopmental disorder (GNAI1-NDD) is characterized by mild-to-profound developmental delay and intellectual disability, hypotonia, neurobehavioral and/or psychiatric manifestations, and epilepsy. To date, at least 26 individuals have been identified with a pathogenic variant in GNAI1 [Deciphering Developmental Disorders Study 2017, Muir et al 2021, Wayhelova et al 2022]. The following description of the phenotypic features associated with this condition is based on these reports. An additional approximately eight individuals with a GNAI1 pathogenic variant have also been reported as part of large cohort studies without phenotypic details [Kosmicki et al 2017, Lim et al 2017, Turner et al 2019, Kaplanis et al 2020, Satterstrom et al 2020, Zhou et al 2022].
Table 2.
Select Features of GNAI1-Related Neurodevelopmental Disorder
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Feature | Proportion of Persons w/Feature | Comment |
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Developmental delay
| 26/26 | Mild to profound |
Hypotonia
| 22/23 | |
Intellectual disability
| 19/19 1 | Mild to profound |
Neurobehavioral/psychiatric manifestations
| 19/24 | Autism, aggression, temper tantrums, hypersensitivity, hand stereotypies |
Epilepsy
| 17/23 | Absence, generalized tonic-clonic, focal-onset impaired awareness |
Abnormal brain MRI
| 10/22 | Global atrophy, delayed myelination, choroid plexus cysts |
Developmental delay has been apparent for all reported individuals with GNAI1-NDD. Developmental delays can range from mild to profound, and the majority of individuals have hypotonia. Sitting and walking milestones are often delayed (20/23 and 21/25, respectively), and some individuals have not or do not achieve sitting or walking (5/23 and 9/25, respectively). Speech can be significantly impaired; many individuals use only a few sounds or words, and ~64% (16/25) of individuals reported remain nonverbal. In general, expressive language skills are more impaired than receptive skills.
Intellectual disability. All individuals with GNAI1-NDD due to a germline variant have intellectual disability ranging from mild to profound (mild/moderate: n=6; severe/profound: n=13). One affected individual who was mosaic for a GNAI1 pathogenic variant did not have intellectual disability [Muir et al 2021].
Autism and other neurobehavioral/psychiatric manifestations. Approximately 80% of reported individuals had one of several neurobehavioral or psychiatric manifestations, including autism spectrum disorder (7/21). Common reported neurobehavioral and psychiatric features include stereotypic behaviors (hand flapping, head banging, hand wringing, repetitive noises, teeth grinding, mouthing behaviors), sensory sensitivities, poor eye contact, temper tantrums, anxiety, agitation, aggression, hyperactivity, and attention-deficit/hyperactivity disorder.
Epilepsy. About 74% of individuals with GNAI1-NDD have had seizures. Age at seizure onset and seizure types are variable. Use of and response to anti-seizure medications (ASMs) is also variable. Some individuals have intractable epilepsy despite multiple ASMs, while others have seizures that resolve [Muir et al 2021].
Seizure onset typically occurs within the first six months of life (median age of onset is five months), although the earliest seizure onset noted was at 36 hours of life, and the oldest reported onset to date is seven years.
Seizure types that are most common include absence, generalized tonic-clonic, and focal-onset impaired awareness (~5 individuals each). Some seizures are nocturnal.
Electroencephalography
(EEG) may show slowing, multifocal activity, other epileptic abnormalities, and encephalopathy. There are no specific EEG findings suggestive of GNAI1-related NDD.
Neuroimaging. About half of individuals have abnormal brain MRI imaging. The most common abnormal findings include global atrophy with progressive volume loss, delayed myelination, and choroid plexus cysts.
Musculoskeletal features. Scoliosis has been reported in six individuals. Hip dysplasia was reported in four individuals, with at least two requiring osteotomy.
Feeding. Feeding difficulties can be present, requiring modified diets (e.g., liquid diet) and/or gastrostomy tube feedings. Obesity and insatiable appetite have also been observed (n=7).
Gastrointestinal issues. Some individuals have constipation.
Ophthalmologic involvement. Strabismus has occurred in a few individuals but does not appear to be common.
Facial features. If present, dysmorphic features are nonspecific in individuals with GNAI1-NDD.
Prognosis. Information about progression and/or regression of neurologic findings is not known. It is also unknown whether life span in individuals with GNAI1-NDD is abnormal; all individuals reported thus far have been children and adolescents. One reported individual is alive at age 18 years [Muir et al 2021], 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.