| Disease |
Key Genetic / Clinical Features |
| 🧠 Fragile X Syndrome |
FMR1 (CGG); X-linked dominant. Intellectual disability, autism, macroorchidism, facial dysmorphism. Expansion via maternal transmission. |
| 🌀 Huntington’s Disease |
HTT (CAG); autosomal dominant. Chorea, psychiatric changes, dementia. Anticipation usually with paternal transmission. |
| 💪 Myotonic Dystrophy (DM1) |
DMPK (CTG); autosomal dominant. Progressive myopathy, grip myotonia, cataracts, endocrine disorders. Expansion via maternal transmission. |
| ⚖️ Spinocerebellar Ataxia (e.g. SCA1) |
ATXN1 (CAG); autosomal dominant. Progressive ataxia, dysarthria, oculomotor abnormalities. Variable parent-of-origin effect. |
| 🌏 DRPLA (Dentatorubral–pallidoluysian atrophy) |
ATN1 (CAG); autosomal dominant. Ataxia, myoclonus, seizures, dementia. More severe with paternal transmission. Notably seen in Japanese population. |