Intellectual Developmental Disorder And Retinitis Pigmentosa
A number sign (#) is used with this entry because of evidence that intellectual developmental disorder and retinitis pigmentosa (IDDRP) is caused by homozygous or compound heterozygous mutation in the SCAPER gene (611611) on chromosome 15q24.
DescriptionIntellectual developmental disorder and retinitis pigmentosa is characterized by mild to moderate intellectual disability and typical features of RP. Patients experience reduced night vision, constriction of visual fields, and reduced visual acuity; optic disc pallor, attenuated retinal blood vessels, and bone-spicule pigmentation are seen on funduscopy. Attention-deficit/hyperactivity disorder is observed in some patients (Tatour et al., 2017).
Clinical FeaturesTatour et al. (2017) studied 4 patients from 3 unrelated families with intellectual developmental disorder and retinitis pigmentosa. Mild to moderate intellectual disability was noted in childhood, and 3 of the patients were also diagnosed with attention-deficit/hyperactivity disorder. Reduced night vision developed in the second and third decades of life, at which time visual acuity was moderately to severely reduced, with concentric constriction of visual fields. Funduscopy revealed optic disc pallor, attenuated retinal blood vessels, and bone-spicule pigmentation. At ages 14 and 15 years, full-field electroretinograms were nonrecordable in 2 affected sisters (family A), reflecting reduced function of the entire retina. However, flash visual evoked potentials were normal in the older sister but abnormal in the younger sister, indicating more advanced degenerative disease involving the central retina in the latter patient. An unrelated affected woman (family B) showed more severe intellectual disability than the 2 sisters, and also exhibited bilateral subcapsular posterior cataracts and alopecia areata. The authors stated that additional genetic and/or environmental factors might be responsible for the observed interindividual and intrafamilial variability in severity of RP and intellectual disability; however, they suggested that the alopecia areata was coincidental. All 4 patients had normal hearing and showed no dysmorphic features; brain imaging, which was performed in 2 of the patients, was normal or nondiagnostic.
Molecular GeneticsBy whole-exome sequencing in 4 patients from 3 unrelated families with intellectual developmental disorder and retinitis pigmentosa, Tatour et al. (2017) found no putative disease-causing mutations in any known retinal dystrophy-associated genes and identified homozygous or compound heterozygous mutations in the SCAPER gene (611611.0001-611611.0004).