Family study identifies genetic mutation associated with choroideremia
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Genetic testing and counseling are advisable in family members of patients with choroideremia, particularly female members of childbearing age, according to a poster presented at the virtual Euretina congress.
“Since the symptoms are very similar to those of retinitis pigmentosa, choroideremia should be considered in the differential diagnosis of males with RP-like symptoms and deafness,” Lucia Lee Ferraro, MD, said in the poster presentation.
Choroideremia is a genetic eye disorder caused by a mutation of the CHM gene, characterized by progressive degeneration of the retina and choroid leading to blindness. Rarely, severe forms may be associated with systemic symptoms, such as hearing loss and intellectual impairment. It mainly affects male patients, while female carriers may have mild signs of the disease, visible on fundus examination.
In a poster, Ferraro presented the case of a 23-year-old man with night blindness, hearing loss and mild intellectual disability in which genetic testing confirmed the diagnosis of choroideremia after years of misdiagnoses. To study the presence of pathogenic variants in the CHM gene, molecular analysis of all family members was performed, in addition to complete ophthalmic examination, including functional and structural testing.
“Given that choroideremia is an X-linked recessive condition, it is very important to know which family members, especially women of childbearing age, are carriers of this mutation,” Ferraro said.
The patient’s best corrected visual acuity was 20/33 in both eyes. Color fundus photography, fundus autofluorescence and OCT showed bilateral degeneration of the choroid, retinal pigment epithelium and photoreceptors, sparing the macula. Perimetry showed significant visual field loss. His mother and two sisters showed features on color fundus photography and fundus autofluorescence characteristic of choroideremia carriers without visual field loss.
Genetic testing showed complete deletion of the CHM gene in the index case, and the three female suspected carriers were heterozygous for the deletion. No other family members were affected, including the grandmother of the index case.
“This implied a de novo mutation in the mother’s proband,” according to Ferraro and colleagues.
While no treatment is currently available for choroideremia, gene therapy might be a hope in the future and is currently being evaluated in trials.
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Ferraro LL, et al. Complete deletion of CHM gene: Study of a family. Presented at: Euretina congress; Sept. 9-12, 2021 (virtual meeting).
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