FB2026_02 , released June 18, 2026
FB2026_02 , released June 18, 2026
Human Disease Model Report: trichothiodystrophy 1, photosensitive
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General Information
Name
trichothiodystrophy 1, photosensitive
FlyBase ID
FBhh0000709
Disease Ontology Term
Parent Disease
Overview

This report describes trichothiodystrophy 1, photosensitive (TTD1), which is a subtype of trichothiodystrophy; TTD1 exhibits autosomal recessive inheritance. The human gene implicated in this disease is Excision Repair Cross-Complementation Group 2 (ERCC2), which is encodes a DNA helicase that is a component of the TFIIH transcription and DNA repair complex. There is a single fly ortholog, Xpd, for which classical loss-of-function alleles, RNAi-targeting constructs, and alleles caused by insertional mutagenesis have been generated. ERCC2 is also implicated in several other human diseases, including a subtype xeroderma pigmentosum (see MIM:126340 and human disease model report FBhh0000205).

The human ERCC2 gene has not been introduced into flies.

Multiple variants of Dmel\Xpd analogous to variants implicated in human disease have been characterized. Most of these correspond to variants implicated in xeroderma pigmentosum, subtype XPD; see FBhh0000205. Variant(s) implicated in human disease tested (as analogous mutation in fly gene): R722W in the fly Xpd gene (corresponds to R722W in the human ERCC2 gene, implicated in TTD1); R112H in the fly Xpd gene (corresponds to R112H in the human ERCC2 gene, implicated in both XPD and TTD1).

Amorphic alleles of the Drosophila Xpd gene are lethal during late embryogenesis; embryonic phenotypes, including radiation sensitivity, have been assayed. Physical and genetic interactions of Dmel\Xpd have been described; see below and in the Xpd gene report.

[updated Jan. 2018 by FlyBase; FBrf0222196]

Disease Summary Information
Parent Disease Summary: trichothiodystrophy
Symptoms and phenotype

Trichothiodystrophy (TTD) is a rare autosomal recessive disorder in which patients have brittle, sulfur-deficient hair that displays a diagnostic alternating light and dark banding pattern under polarizing microscopy. TTD patients display a wide variety of clinical features, including cutaneous, neurologic, and growth abnormalities. Common additional clinical features are ichthyosis (rough, thick, and scaly skin), intellectual/developmental disabilities, decreased fertility, ocular abnormalities, short stature, and infections. There are both photosensitive and non-photosensitive forms of the disorder. TTD patients have not been reported to have a predisposition to cancer (summary by Faghri et al., 2008; pubmed:18603627). [from MIM:601675; 2018.01.22]

Specific Disease Summary: trichothiodystrophy 1, photosensitive
OMIM report

[TRICHOTHIODYSTROPHY 1, PHOTOSENSITIVE; TTD1](https://omim.org/entry/601675)

Human gene(s) implicated

[ERCC EXCISION REPAIR 2, TFIIH CORE COMPLEX HELICASE SUBUNIT; ERCC2](https://omim.org/entry/126340)

Symptoms and phenotype

TTD1 is a photosensitive form of trichothiodystrophy. [from MIM:601675; 2018.01.22]

Genetics

Photosensitive trichothiodystrophy-1 (TTD1) is caused by homozygous or compound heterozygous mutation in the ERCC2/XPD gene. [from MIM:601675; 2018.01.22]

Cellular phenotype and pathology
Molecular information

ERCC2 encodes a helicase subunit of transcription/repair factor TFIIH, which functions in nucleotide excision repair. [from MIM:601675, MIM:126340; 2018.01.22]

External links
Disease synonyms
photosensitive trichothiodystrophy
TTD1
TTDP
Ortholog Information
Human gene(s) in FlyBase
    Human gene (HGNC)
    D. melanogaster ortholog (based on DIOPT)
    Comments on ortholog(s)

    One to one (1 human to 1 Drosophila).

    Other mammalian ortholog(s) used
      D. melanogaster Gene Information (1)
      Gene Snapshot
      Xeroderma pigmentosum D (Xpd) encodes a DNA helicase that is a subunit of the basal transcription and DNA repair factor TFIIH. [Date last reviewed: 2019-03-21]
      Gene Groups / Pathways
      Comments on ortholog(s)

      High-scoring ortholog of human ERCC2 (1 Drosophila to 1 human). Dmel\Xpd shares 69% identity and 84% similarity with the human gene.

      Orthologs and Alignments from DRSC
      DIOPT - DRSC Integrative Ortholog Prediction Tool - Click the link below to search for orthologs in Humans
      Other Genes Used: Viral, Bacterial, Synthetic (0)
        Summary of Physical Interactions (11 groups)
        protein-protein
        Interacting group
        Assay
        References
        anti bait coimmunoprecipitation, western blot
        pull down, western blot, anti tag coimmunoprecipitation, anti tag western blot
        anti tag coimmunoprecipitation, anti tag western blot
        anti tag coimmunoprecipitation, anti tag western blot, western blot, anti bait coimmunoprecipitation
        anti bait coimmunoprecipitation, western blot
        anti tag coimmunoprecipitation, peptide massfingerprinting, experimental knowledge based
        anti tag coimmunoprecipitation, peptide massfingerprinting, experimental knowledge based
        pull down, anti tag western blot, anti tag coimmunoprecipitation
        anti tag coimmunoprecipitation, western blot
        anti tag coimmunoprecipitation, peptide massfingerprinting, experimental knowledge based
        anti bait coimmunoprecipitation, western blot
        Alleles Reported to Model Human Disease (Disease Ontology) (10 alleles)
        Models Based on Experimental Evidence ( 10 )
        Allele
        Disease
        Evidence
        References
        Modifiers Based on Experimental Evidence ( 0 )
        Allele
        Disease
        Interaction
        References
        Alleles Representing Disease-Implicated Variants
        Genetic Tools, Stocks and Reagents
        Sources of Stocks
        Contact lab of origin for a reagent not available from a public stock center.
        Bloomington Stock Center Disease Page
        Related mammalian, viral, bacterial, or synthetic transgenes
        Allele
        Transgene
        Publicly Available Stocks
        Selected Drosophila transgenes
        Allele
        Transgene
        Publicly Available Stocks
        RNAi constructs available
        Allele
        Transgene
        Publicly Available Stocks
        Selected Drosophila classical alleles
        Allele
        Allele class
        Mutagen
        Publicly Available Stocks
        References (7)