Trichothiodystrophy (TTD) is an autosomal recessive disorder of hair. It is indicated by brittle hair and intellectual impairment. Breaking of the word Trichothiodystrophy is – tricho-hair; thio-sulphur; dystrophy-wasting away. The literary meaning being, bad nourishment. TTD is linked with a variety of symptoms connected with organs of the ectoderm and neuroectoderm. It is sometimes called PIBIDS, a term that refers to the association of Photosensitivity Ichthyosis, Brittle hair, Intellectual impairment, Decreased fertility, and Short stature. Without photosensitivity the condition has been referred to as IBIDS, and without ichthyosis, BIDS. Many patients have recurrent infections, and abnormalities of the bone and teeth may also occur.
The defining feature of Trichothiodystrophy is brittle hair, which is sulfur deficient and, when examined with a microscope and polarized light, exhibits a characteristic light and dark (tiger tail) banding.
Most cases of the photosensitive form of Trichothiodystrophy result from mutations in one of the three genes: ERCC2, ERCC3, orGTF2H5. The proteins produced from these genes work together as part of a group of proteins called the general transcription factor IIH (TFIIH) complex. This complex is involved in the repair of DNA damage, which can be caused by UV radiation from the sun. The TFIIH complex also plays an important role in gene transcription, which is the first step in protein production.
Mutations in the ERCC2, ERCC3, or GTF2H5 genes decrease the amount of TFIIH complex within cells, which hampers both DNA repair and gene transcription. An incapacity to repair DNA damage probably underlies the sun sensitivity in affected individuals. Studies suggest that many of the other features of Trichothiodystrophy may result from problems with the transcription of genes required for normal development before and after birth.
How is Trichothiodystrophy inherited?
This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
- The classic tiger-tail appearance of affected hair is denoted by bright and dark bands along the hair shaft under polarized light microscopy and low sulfur content, is a clinical marker for a neuroectodermal abnormality.
- Light microscopy – Hair shafts show wavy contour and folding along their axis.
- Scanning electron microscopy – Completely flat hair with trichoschisis (brittle hair) may be revealed. Severe cuticular and secondary cortical degeneration along almost the entire hair shaft, with decreased or absent cuticular pattern and abnormal ridging and fluting.
- There is no specific treatment available for TTD.
- Management of TTD in case of children is symptomatic.
- Family psychological and social support is needed.
- Children should be advised and educated to avoid exposure to the sun and any kind of injury or trauma by aggressive combing or hair dressing because of the particularly weak hair shaft.