Mosaic skin disorders - deep sequencing

Gene: TSC1

Green List (high evidence)

Comment on list classification: There are numerous individuals reported in literature diagnosed with Tuberous sclerosis complex, harbouring heterozygous mosaic TSC1 variants. Deep sequencing of multiple patient samples is advised, as the variants often occur at very low frequencies (3-5%). Variants are sometimes detected in skin biopsy samples only - not in blood or saliva. Based on the available evidence, TSC1 should be promoted to Green for Mosaic skin disorders - deep sequencing.

Created: 3 Dec 2025, 5:08 p.m. | Last Modified: 3 Dec 2025, 5:11 p.m.

Panel Version: 3.16

Tuberous sclerosis complex present with hamartomatous tumors affecting multiple organs, including the skin: facial angiofibroma, ungual fibroma, and shagreen patch (PMID: 37141891).

PMID: 37356622 Blasco-Perez et al., 2023
Cohort of Tuberous sclerosis complex (TSC) patients. Seq method: deep coverage NGS seq of TSC1 and TSC2 - average coverage >400x. 8/29 variants were detected in mosaicism, 4 at extremely low levels ( <16%). Variants are sometimes detected in skin biopsy samples only - not in blood or saliva.
Patients with TSC1 variants:
10 non-mosaic heterozygous cases;
Patient 6: mosaic variant TSC1:c.994del, p.Ser332Profs∗6; variant detected in saliva (36%) and affected skin (42%); blood sequencing not performed
Patient 12: mosaic variant TSC1:c.2101_2107del, p.Gln701Serfs∗21 - 4% in peripheral blood

PMID: 37141891 Klonowska et al., 2023
Cohort of 95 individuals with TSC and confirmed mosaicism. Method: Deep massively parallel sequencing (MPS) (median read depth ≥ 500×). 9/95 individuals had variants in TSC1, and 86/95 patients had variants detected in TCS2.
The cohort included patients previously reported in PMID: 26540169 Tyburczy et al., 2015, as well as PMID: 31160751 Giannikou et al., 2019; PMID: 31114024 Treichel et al., 2019; PMID: 32461669 Ogorek et al., 2020.

PMID: 26540169 Tyburczy et al., 2015
Cohort of 53 patients with TSC and no mutation identified in previous testing. Median read depth was ≥ 5,000x for long-range PCR, and ≥ 500x in hybrid capture method. All 53 TSC patients had skin involvement.
Reported 4 patients with non-mosaic heterozygous TSC1 variants (allele freq = 50%), as well as 4 mosaic cases (allele freq <50%):
P53: 22yo male; TSC1 c.1776delG - 30% mutant allele in saliva and blood
P2: 20yo male; c.2689C>T; p.Q897* in TSC1 - 15% mutant allele in blood
P6: 4yo male; TSC1 c.2111_2112delAT - 4.7% in blood and normal skin
P5f: 57yo female; TSC1 c.2374C>T; p.Q792* - 3.3% in blood

This gene is associated with AD Tuberous sclerosis-1, MIM:191100 in OMIM (accessed 3rd Dec 2025).

Created: 3 Dec 2025, 4:59 p.m. | Last Modified: 3 Dec 2025, 5:11 p.m.

Panel Version: 3.16

Mode of inheritance
MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted

Phenotypes
Tuberous sclerosis-1, OMIM:191100; tuberous sclerosis 1, MONDO:0008612

Publications

• 26540169
• 31160751
• 31114024
• 32461669
• 37141891
• 37356622

Green List (high evidence)

Mosaic, potential for germline transmission to offspring
Sources: Expert Review

Created: 31 Oct 2025, 2:13 p.m.

Mode of inheritance
Other

Phenotypes
Cutaneous pigmentary abnormalities, and/or other aspects of germline TSC disease

Publications

• PMID: 37356622