Overlapping Genes/Symptoms
8-year-old male referred for genetic testing for Leber congenital amaurosis
Suspected clinical diagnosis: Leber congenital amaurosis (LCA), an autosomal recessive, early-onset severe retinal disease that results in total blindness at an early age
Presenting complaint: Decreased visual acuity, congenital nystagmus, reduced colour vision, both eyes
Medical history: No significant systemic ophthalmologic history
Family history: It is apparent from the pedigree chart that the proband’s (patient) maternal great-grandfather and his brothers also had similar symptoms that are associated with a retinal dystrophy. The pedigree chart is consistent with X-linked inheritance
Eye exam and imaging
- Fundus exam: appeared grossly normal
Additional information: Upon questioning, all affected males in the older generation still have vision with little progression over time. This, along with the X-linked pattern, raised suspicion towards blue cone monochromacy (BCM) and away from LCA
Genetic test and results: BCM specific testing was positive for a hemizygous deletion covering part of the LCR and OPN1LW promoter
Final diagnosis: Blue cone monochromacy
Key Takeaways
Family history can be crucial in establishing a diagnosis.[1] In this case, the patient’s prognosis went from becoming completely blind to now having a more favourable visual outcome.
Note: BCM is often excluded from inherited retinal disease (IRD) genetic testing panels; therefore, it is important to ensure that the appropriate test is ordered.
This case study is based on a licensed genetic counsellor's in-office experience. It is based on a real patient with changes made for privacy considerations.
