Repeat Disorders
STR: TYMS_CPUM_ACCATC
PMID 40589716 reports a single Thai family with 15-year-old monozygotic twin girls and congenital progressive universal melanosis (diffuse hyperpigmentation from birth). Both carry biallelic GATGGT hexanucleotide expansions in intron 3 of TYMS, reported as 210-259 repeats. Both parents are unaffected heterozygous carriers at age 56 (106/230-245 and 93/217-224).
The twins are monozygotic (KING kinship 0.4934).
In-house long-read controls (n=236) had 42-172 repeats, with 47% at 106 and no control carrying a long allele on both chromosomes.
Reduced TYMS expression is the proposed mechanism, but TYMS RNA in fibroblasts and PBMCs and protein in fibroblasts all fell within the control range. Further probands/families are required to confirm the gene-disease association.
Sources: LiteratureCreated: 2 Sep 2026, 10:06 p.m.
Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal
Phenotypes
Congenital progressive universal melanosis MONDO:0013648
Publications
Str: tyms_cpum_accatc has been classified as Red List (Low Evidence).
STR: TYMS_CPUM_ACCATC was added STR: TYMS_CPUM_ACCATC was added to Repeat Disorders. Sources: Literature Mode of inheritance for STR: TYMS_CPUM_ACCATC was set to BIALLELIC, autosomal or pseudoautosomal Publications for STR: TYMS_CPUM_ACCATC were set to 40589716 Phenotypes for STR: TYMS_CPUM_ACCATC were set to Congenital progressive universal melanosis MONDO:0013648 Review for STR: TYMS_CPUM_ACCATC was set to RED