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HEREDITARY MONOGENIC DISEASES

           

Complete achromatopsia (type 2) and Incomplete achromatopsia

Achromatopsia (ACHM), as well known as complete or incomplete color blindness is a rare autosomal recessive retinal disorder, characterized by color blindness, nystagmus, photophobia and severely reduced visual acuity caused by the absence or deficiency in cone functioning.

The global prevalence is estimated at 1/30,000-1/50,000 births.

Achromatopsia is characterized by reduced visual acuity, pendular nystagmus, increased sensitivity to light (photophobia), small central scotoma and reduced or total loss of the ability to distinguish colors.

The majority of individuals who suffer from achromatopsia present a complete absence of activity in all three types of cones (total ACHM). Rarely, they present incomplete variants with similar but generally less severe symptoms.

The diagnosis is based on an ophthalmological clinical examination, psychophysical and electrophysiological tests (electroretinography / ERG) in which loss of photopic response is observed. The optical coherence tomography shows a progressive interruption and/or loss of union between the internal/external segments of the photoreceptors, and an attenuation of the retinal pigment epithelium (RPE) in the macular region.

Confirmation diagnosis is made by molecular genetic analysis.

Five genes (GNAT2 (1p13), PDE6C (10q24), PDE6H (12p13), CNGA3 (2q11.2) and CNGB3 8q21.3)) have been associated with ACHM. Mutations in CNGB3 are predominant, followed by those in CNGA3, while the rest are rare causes of ACHM.

Genetic counseling is recommended. ACHM is inherited with an autosomal recessive pattern.

ACHM is usually a stationary disease, although macular degeneration can occur. The treatment is symptomatic and it includes regular follow-up eye exams.

GENE OR REGION STUDIED


  • PDE6H
  • CNGA3