## Inheritance Patterns in Retinitis Pigmentosa **Key Point:** Autosomal recessive RP is the most common genetic form, accounting for ~50% of all RP cases, though autosomal dominant and X-linked forms also occur with significant frequency. ### Distribution of RP Inheritance Patterns | Inheritance Pattern | Frequency | Key Features | | --- | --- | --- | | Autosomal Recessive | ~50% | Most common; often earlier onset; more severe progression | | Autosomal Dominant | ~30% | Variable expressivity; later onset; slower progression | | X-linked Recessive | ~15% | Males predominantly affected; females may show carrier signs | | Mitochondrial | <5% | Rare; maternal inheritance; variable penetrance | ### Why Autosomal Recessive is Most Common 1. **Gene frequency:** Genes causing autosomal recessive RP (e.g., ABCA4, RPE65, CILIA genes) are more prevalent in the general population 2. **Consanguinity:** Higher rates in populations with consanguineous marriages 3. **Genetic heterogeneity:** Multiple genes can cause autosomal recessive RP, increasing overall prevalence **High-Yield:** In clinical practice, when a patient presents with RP without a family history, autosomal recessive inheritance should be suspected. Conversely, a clear vertical transmission pattern across generations suggests autosomal dominant inheritance. **Clinical Pearl:** X-linked RP typically affects males more severely, with females showing peripheral retinal changes or a "carrier phenotype" with patchy pigmentation. This sex-specific pattern is a diagnostic clue. **Mnemonic:** **AR-50, AD-30, XL-15** — Autosomal Recessive 50%, Autosomal Dominant 30%, X-Linked 15% (approximate frequencies). 
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