C3256T

# **General Information**

| **Position** | **3256** | **Variant** | **m.3256C\>T** | **Locus** | **MT\-TL1** | **RNA** | **tRNA Leu (UUR)** |
| --- | --- | --- | --- | --- | --- | --- | --- |
| **Homoplasmy** | \- | **Heteroplasmy** | \+ | **mitoTIP** | Pathogenic | **Pathogenicity** | Cfrm \[LP] |

"Pathogenicity" status is derived from published literature or predictions from bioinformatics tools. Researchers and clinicians are cautioned that additional data and/or analysis may still be necessary to confirm the pathological significance of these variants. For more information, please see [Mitofam Info](https://mitofam.com/doc/385/).

# **Pedigree Information**

The **m.3256C\>T** variant in MT\-TL1 has been reported in 5 pedigrees. To date, 5 carriers have been reported. Reported mutation loads ranged from 4% to 85%, with a median of 56\.6% overall; affected carriers showed mutation loads from 4% to 85%, with a median of 56\.6%. In one affected carrier, a marked tissue\-specific difference was observed, with higher mutation loads in muscle (69%) than in blood (4%). In one affected carrier, a marked tissue\-specific difference was observed, with higher mutation loads in muscle (85%) than in blood (35%). The main clinical manifestations among affected carriers included MELAS, progressive multisystem disorder, psychosis, bilateral central vision loss, deltoid weakness, diabetes mellitus, generalized tonic\-clonic seizures, hearing loss, and other features.

| **No.** | **Position** | **Variant** | **Family ID** | **Nationality** | **Diseases** | **Unaffected Maternal Relatives** | **Affected Maternal Relatives** | **Publication Year** | **PMID/Ref** | **Note** |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1 | 3256 | m.3256C\>T | C3256T\-F1 | USA | Progressive multisystem disorder, generalized tonic\-clonic seizures, ptosis, ophthalmoparesis, hearing loss, diabetes mellitus, hypothyroidism, bilateral central vision loss, optic disk pallor, retinal pigment degeneration, limb myoclonus, neck muscle weakness, deltoid weakness, mild ataxia, vertigo, nausea | ND | ND | 1993 | [8254046](https://pubmed.ncbi.nlm.nih.gov/8254046/) |  |
| 2 | 3256 | m.3256C\>T | C3256T\-F2 | Japan | MELAS | ND | ND | 1994 | [7804130](https://pubmed.ncbi.nlm.nih.gov/7804130/) |  |
| 3 | 3256 | m.3256C\>T | C3256T\-F3 | Japan | Psychosis, progressing dementia | ND | ND | 2000 | [10953207](https://pubmed.ncbi.nlm.nih.gov/10953207/) |  |
| 4 | 3256 | m.3256C\>T | C3256T\-F4 | Denmark | MELAS | ND | ND | 2003 | [12972383](https://pubmed.ncbi.nlm.nih.gov/12972383/) |  |
| 5 | 3256 | m.3256C\>T | C3256T\-F5 | China | MELAS | ND | ND | 2025 | [40135206](https://pubmed.ncbi.nlm.nih.gov/40135206/) |  |

# **Carrier Information**

| **No.** | **Position** | **Variant** | **Family ID** | **Carrier ID** | **Type (Fam/De novo/Uninf)** | **Gender (F/M)** | **Proband (Y/N)** | **Affected (Y/N)** | **Die/Alive(D/A)** | **Age** | **Blood Mutant Level** | **Muscle Mutant level** | **Urine Mutant level** | **Other Mutant level** | **Clinical Features** | **Note** |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1 | 3256 | m.3256C\>T | C3256T\-F1 | C3256T\-F1\-P1 | Uninf | M | Y | Y | A | 28 | 4% | 69% | / | 6% (F) | Progressive multisystem disorder, generalized tonic\-clonic seizures, ptosis, ophthalmoparesis, hearing loss, diabetes mellitus, hypothyroidism, bilateral central vision loss, optic disk pallor, retinal pigment degeneration, limb myoclonus, neck muscle weakness, deltoid weakness, mild ataxia, vertigo, nausea |  |
| 2 | 3256 | m.3256C\>T | C3256T\-F2 | C3256T\-F2\-P1 | De novo | ND | Y | Y | A | ND | / | / | / | / | MELAS |  |
| 3 | 3256 | m.3256C\>T | C3256T\-F3 | C3256T\-F3\-P1 | Uninf | M | Y | Y | A | 29 | / | 77\.4% | / | 44\.4% (Liver), 68\.8% (Heart) | Psychosis, progressing dementia |  |
| 4 | 3256 | m.3256C\>T | C3256T\-F4 | C3256T\-F4\-P1 | Uninf | F | Y | Y | A | 36 | 35% | 85% | / | / | MELAS |  |
| 5 | 3256 | m.3256C\>T | C3256T\-F5 | C3256T\-F5\-P1 | Uninf | F | Y | Y | A | 32 | / | / | / | / | MELAS |  |

For abbreviations and other usage instructions, please see [Mitofam Info](https://mitofam.com/doc/385/).