Clinical Description
More than 200 individuals with an approximately 2.0-Mb heterozygous recurrent deletion at 15q13.3 have been reported [Lowther et al 2015, Pavone et al 2020]. The following description of the phenotypic features associated with this condition is based on these reports. Note: To date, no clinically significant differences have been reported between individuals with deletions BP3-BP5 or BP3-BP4 compared to those with BP4-BP5. However, this chapter focuses specifically on those with the BP4-BP5 deletion [Pavone et al 2020], as this recurrent deletion accounts for about 94% of deletions in this recurrent deletion region [Lowther et al 2015].
Table 2.
15q13.3 Recurrent Deletion: Frequency of Select Features
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Feature | % of Persons w/Feature 1 | Comment |
---|
Developmental delay / intellectual disability | ~59% | Accounting for ascertainment 2 |
Behavioral findings | ~35% 3 | |
Seizures/epilepsy | ~30% | |
Minor dysmorphic facial features | ~16% | No specific areas of the face are consistently dysmorphic & no recognizable facial features have been reported [Pavone et al 2020]. |
Hypotonia | ~14% | |
Schizophrenia | ~11% | |
Autism spectrum disorder | ~10% | |
Mood disorders | ~10% | |
ADHD | ~7% | |
AHDH = attention-deficit/hyperactivity disorder
- 1.
- 2.
Individuals with developmental delay / intellectual disability are more likely to undergo advanced genetic testing, including chromosomal microarray analysis, than individuals without this finding [Ziats et al 2016].
- 3.
Percentage of reported individuals with behavior problems ranges from 35% to 51%, although the report that found a high percentage of behavior problems excluded publications that contain fewer than three affected individuals and did not correct for ascertainment bias.
Intellectual disability and developmental delay. Accounting for ascertainment, intellectual disability or developmental delay has been observed in approximately 59% of individuals with the 15q13.3 recurrent deletion [Lowther et al 2015, Pavone et al 2020]. Developmental delays are mainly delays in speech acquisition and cognitive function rather than motor disability, although hypotonia can contribute to mild motor delays (see Hypotonia). In the majority of individuals, cognitive impairment is mild. However, a subset of individuals with moderate-to-severe disability have been reported [Ben-Shachar et al 2009, van Bon et al 2009, Lowther et al 2015]. In a small study of 18 individuals with 15q13.3 deletions (15 with the recurrent BP4-BP5 deletion and 3 others with larger deletions that included BP3-BP5) who underwent comprehensive IQ assessment, the average verbal and nonverbal subcomponents of the IQ test were 64.3 and 60.1, respectively [Ziats et al 2016], suggesting no significant difference between verbal and nonverbal IQ scores in affected individuals.
Some individuals with the 15q13.3 recurrent deletion have no discernible clinical features, including developmental or cognitive delays. However, data on 23,838 adult "controls" (individuals who did not undergo genetic testing for an indication of developmental concerns or other clinical features) detected no 15q13.3 deletions [Lowther et al 2015]. Another study reporting on a population-based sample (n=101,655) identified 25 such recurrent deletions (0.025%) [Stefansson et al 2014].
Epilepsy. About 30% of individuals with the 15q13.3 recurrent deletion are diagnosed with epilepsy [Lowther et al 2015, Pavone et al 2020]. Children commonly present with absence seizures that start in childhood, but this could be accompanied by atypical features such as persistence into adolescence, early onset, absence status epilepticus, and treatment resistance. More rare generalized seizure types (such as myoclonic absence and atonic seizures in addition to focal with impaired awareness non-motor onset seizures) were also observed. EEG may show a mixture of generalized and focal findings. The presence of combined seizure types and EEG findings should be treated with caution, as some anti-seizure medications (ASMs) (i.e., specific sodium channel blockers such as oxcarbazepine) could potentially worsen seizures (see Management), although this requires further study. Valproate appeared effective, but more studies are needed to confirm the effectiveness of other ASMs and therapies [Whitney et al 2021].
Hypotonia. In general, hypotonia is mild and body muscular tone improves during childhood. Walking without support is often achieved between age 12 months and three years (average: 21.5 months). Hypotonia likely contributes to the delay in achievement of motor milestones reported in some individuals.
Neuroimaging. Brain MRI findings are not frequently observed or reported; they include rare reports of arachnoid cysts, cerebellar vermis hypoplasia, ventricular dilatation, corpus callosal agenesis, focal cortical dysplasia, and heterotopia. Other nonspecific findings such as mild prominence of extra cerebral spaces, focal volume loss, prominent cerebellar folia, and T2 hyperintensities within the subcortical white matter have also been reported [Whitney et a 2021].
Neuropsychiatric disorders. Behavioral/psychiatric findings are present in about one third of individuals and mainly include autism spectrum disorder, attention-deficit/hyperactivity disorder (ADHD), mood disorder, self-mutilation, and aggressive and/or impulsive behavior [Lowther et al 2015].
In three studies, the 15q13.3 recurrent deletion was enriched in cohorts of individuals with schizophrenia compared to controls [International Schizophrenia Consortium 2008, Stefansson et al 2008, Lowther et al 2015]. Accounting for ascertainment bias, schizophrenia may be present in 11% of adult individuals with the 15q13.3 recurrent deletion [Lowther et al 2015].
Facial features. No specific dysmorphic features have been observed. If present, dysmorphic features are nonspecific [Pavone et al 2020].
Rare features. Severe congenital malformations are uncommon.
Heart. Structural congenital cardiac malformations are seen in a low number of individuals (3%) [
Lowther et al 2015]. Hypercholesterolemia has been occasionally reported.
Ocular anomalies have been reported in 6% of individuals [
Pavone et al 2020], most frequently strabismus and astigmatism.
Hearing. In general, children and adults have normal hearing. However, temporary hearing loss due to recurrent ear infections in infancy may occur.
Growth. Abnormalities in growth may occur (both undergrowth and overgrowth), although most children grow normally.
Other. It is unclear if the following represent rare findings of the 15q13.3 recurrent deletion or chance co-occurrences that are unrelated [van Bon et al 2009, Lowther et al 2015, Pavone et al 2020]:
Gastrointestinal findings including gastrointestinal reflux disease, hiatal hernia, and diverticulosis
Endocrine anomalies such as hypothyroidism and insulin-resistant diabetes
Urogenital
findings such as renal cyst, urethral stricture, and nephrolithiasis
Placenta previa, present of 1.6% in probands (i.e., ≤5x the standard population estimates). However, further studies including the investigation of possible confounding risk factors are needed to confirm this finding [
Lowther et al 2015].