Overview
This lecture discusses the main causes (etiologies) of bilateral cataracts in children, focusing on genetic, metabolic, and systemic factors, with an emphasis on characteristic features and inheritance.
Etiologies of Bilateral Cataract in Children
- Main causes: genetic mutations, metabolic syndromes, chromosomal anomalies, TORCH infections, and systemic syndromes.
- Genetic mutations are the most common cause of bilateral cataracts in pediatrics.
- Most common inheritance: autosomal dominant, followed by autosomal recessive and X-linked.
- Autosomal recessive cases are often seen in families with consanguinity.
- More than 15 genes have been linked, mostly affecting crystallin and connexin proteins.
Genetic Bilateral Cataracts
- Typically not associated with other systemic or ocular abnormalities.
- Isolated inherited congenital cataracts have better visual prognosis than syndromic cases.
Metabolic Causes of Bilateral Cataracts
- Six main metabolic causes: galactosemia, Wilson disease, Fabry disease, Lowe syndrome, diabetic cataract, and hypocalcemic (parathyroid tetany).
Galactosemia
- Autosomal recessive disorder; absence of enzymes in galactose metabolism (galactokinase, GALT, galactose epimerase).
- Leads to galactitol accumulation in the lens, causing osmotic swelling and cataract.
- Three types exist depending on the enzyme deficiency; type 1 (GALT deficiency) is most severe.
- Typical "oil droplet" cataract seen on retroillumination.
- Early removal of milk products can prevent or reverse early cataract formation.
Wilson Disease
- Autosomal recessive copper metabolism disorder (ATP7B gene).
- Features: high blood copper, low ceruloplasmin.
- Ocular findings: Kayser-Fleischer ring (corneal copper deposit) and "sunflower cataract" (petaloid, golden-green).
- Associated with liver and brain involvement.
Fabry Disease
- X-linked recessive lysosomal storage disorder (α-galactosidase A deficiency); males primarily affected.
- Accumulation of ceramide trihexoside (GL3).
- Features: angiokeratoma skin lesions, "screw vessels" in conjunctiva, vortex keratopathy, and almost universal wedge/spoke-shaped posterior capsular cataract.
Lowe Syndrome
- X-linked recessive disorder (OCRL1 gene); affects males more.
- Syndrome: aminoaciduria/proteinuria, CNS and kidney involvement.
- Ocular: nearly universal bilateral cataracts, microphakia, possible congenital glaucoma, posterior lenticonus.
Diabetic Cataract
- Rare, rapid-onset in young type 1 diabetics.
- Acute hyperglycemia leads to sorbitol accumulation, causing lens hydration and "snowflake" or "snowstorm" cataract.
- Increased lens curvature may cause myopia.
Hypocalcemic (Parathyroid Tetany) Cataract
- Due to parathyroid atrophy/removal, resulting in hypocalcemia.
- Disrupted lens membrane transport increases lens sodium and water, causing hydration and cataract.
Key Terms & Definitions
- Autosomal Dominant/Recessive — Types of genetic inheritance patterns.
- X-linked Recessive — Gene located on the X chromosome, typically affects males.
- Galactosemia — Inherited inability to metabolize galactose.
- GALT (galactose 1-phosphate uridyl transferase) — Enzyme deficient in classic galactosemia.
- Galactitol — Osmotic alcohol from alternative galactose metabolism, causes lens swelling.
- Kayser-Fleischer Ring — Copper deposit at corneal periphery in Wilson disease.
- Sunflower Cataract — Petaloid, golden-green lens opacity in Wilson disease.
- Fabry Disease — X-linked disorder, α-galactosidase A deficiency, leads to "spoke" cataracts.
- Lowe Syndrome — X-linked disorder with bilateral cataracts, kidney, and CNS involvement.
- Sorbitol — Osmotic sugar alcohol accumulating in the lens in diabetes.
- Snowflake/Snowstorm Cataract — Dense white subcapsular lens opacities due to diabetes.
- Posterior Lenticonus — Outpouching of posterior lens capsule, can occur with Lowe syndrome.
Action Items / Next Steps
- Review enzyme pathways and typical clinical features for each metabolic cause of cataract.
- Prepare to answer which infection causes "snowflake" opacities in the cornea (not just the lens).
- Study characteristic cataract morphologies and related systemic findings for exam preparation.