Trichothiodystrophy: report of a new case with severe nervous system impairment

Ribosomal Dysfunction Is a Common Pathomechanism in Different Forms of Trichothiodystrophy

Mutations in a broad variety of genes can provoke the severe childhood disorder trichothiodystrophy (TTD) that is classified as a DNA repair disease or a transcription syndrome of RNA polymerase II. In an attempt to identify the common underlying pathomechanism of TTD we performed a knockout/knockdown of the two unrelated TTD factors TTDN1 and RNF113A and investigated the consequences on ribosomal biogenesis and performance. Interestingly, interference with these TTD factors created a nearly uniform impact on RNA polymerase I transcription with downregulation of UBF, disturbed rRNA processing and reduction of the backbone of the small ribosomal subunit rRNA 18S. This was accompanied by a reduced quality of decoding in protein translation and the accumulation of misfolded and carbonylated proteins, indicating a loss of protein homeostasis (proteostasis). As the loss of proteostasis by the ribosome has been identified in the other forms of TTD, here we postulate that ribosomal dysfunction is a common underlying pathomechanism of TTD.

A novel MPLKIP-variant in three Finnish patients with non-photosensitive trichothiodystrophy type 4

Trichothiodystrophy is a group of multisystem neuroectodermal disorders with dysplastic hair as the cardinal symptom. We describe three patients from two Finnish families in whom whole-exome sequencing revealed a novel homozygous variant, c.26del, p.(Pro9Glnfs*144) in the MPLKIP-gene, confirming the diagnosis of non-photosensitive trichothiodystrophy type 4 (TTD4). The variant was confirmed by Sanger sequencing and inherited from unaffected carrier parents. This report adds to the literature by expanding the genetic and phenotypic spectra of MPLKIP-related trichothiodystrophy. We describe dysmorphic features in the patients and provide a comparison of clinical characteristics in patients with TTD4 reported to date.

Mutations in the TTDN1 gene are associated with a distinct trichothiodystrophy phenotype

Trichothiodystrophy (TTD) is a rare multisystem disorder, characterized by sulfur deficient hair with alternating dark and light “tiger tail” banding on polarized light microscopy. TTD is caused by mutations in DNA repair/transcription genes XPD, XPB or TTDA, and in TTDN1, a gene of unknown function. While most TTD patients are photosensitive, patients with TTDN1 mutations were reported to be non-photosensitive. We followed a cohort of 36 TTD patients from 2001 to 2013. We describe 5 patients from 4 families with defects in the TTDN1 gene: 4 had no photosensitivity while 1 patient exhibited cutaneous burning. Deep phenotyping of our cohort revealed differences between the patients with and without TTDN1 mutations. Delayed bone age and seizure disorders were overrepresented in the TTDN1 group (p=0.009 and p=0.024, respectively), while some characteristic TTD clinical, laboratory, and imaging findings were absent. The 3 oldest TTDN1 patients displayed autistic behaviors in contrast to the characteristic friendly, socially interactive personality in the other patients. DNA sequencing revealed deletion mutations in TTDN1 ranging in size from a single base pair to over 120kb. These data identify a distinct phenotype relationship in TTD caused by TTDN1 mutations and suggest a different mechanism of disease.

Trichothiodystrophy: a systematic review of 112 published cases characterises a wide spectrum of clinical manifestations

Trichothiodystrophy (TTD) is a rare, autosomal recessive disease, characterised by brittle, sulfur deficient hair and multisystem abnormalities. A systematic literature review identified 112 patients ranging from 12 weeks to 47 years of age (median 6 years). In addition to hair abnormalities, common features reported were developmental delay/intellectual impairment (86%), short stature (73%), ichthyosis (65%), abnormal characteristics at birth (55%), ocular abnormalities (51%), infections (46%), photosensitivity (42%), maternal pregnancy complications (28%) and defective DNA repair (37%). There was high mortality, with 19 deaths under the age of 10 years (13 infection related), which is 20-fold higher compared to the US population. The spectrum of clinical features varied from mild disease with only hair involvement to severe disease with profound developmental defects, recurrent infections and a high mortality at a young age. Abnormal characteristics at birth and pregnancy complications, unrecognised but common features of TTD, suggest a role for DNA repair genes in normal fetal development.

Identification of C7orf11 (TTDN1) gene mutations and genetic heterogeneity in nonphotosensitive trichothiodystrophy

We have identified C7orf11, which localizes to the nucleus and is expressed in fetal hair follicles, as the first disease gene for nonphotosensitive trichothiodystrophy (TTD). C7orf11 maps to chromosome 7p14, and the disease locus has been designated "TTDN1" (TTD nonphotosensitive 1). Mutations were found in patients with Amish brittle-hair syndrome and in other nonphotosensititive TTD cases with mental retardation and decreased fertility but not in patients with Sabinas syndrome or Pollitt syndrome. Therefore, genetic heterogeneity in nonphotosensitive TTD is a feature similar to that observed in photosensitive TTD, which is caused by mutations in transcription factor II H (TFIIH) subunit genes. Comparative immunofluorescence analysis, however, suggests that C7orf11 does not influence TFIIH directly. Given the absence of cutaneous photosensitivity in the patients with C7orf11 mutations, together with the protein's nuclear localization, C7orf11 may be involved in transcription but not DNA repair.

Trichothiodystrophy: update on the sulfur-deficient brittle hair syndromes

Trichothiodystrophy (TTD) refers to a heterogeneous group of autosomal recessive disorders that share the distinctive features of short, brittle hair and an abnormally low sulfur content. Within the spectrum of the TTD syndromes are numerous interrelated neuroectodermal disorders. The TTD syndromes show defective synthesis of high-sulfur matrix proteins. Abnormalities in excision repair of ultraviolet (UV)-damaged DNA are recognized in about half of the patients. Three distinct autosomal recessive syndromes are associated with nucleotide excision repair (NER) defects: the photosensitive form of TTD, xeroderma pigmentosum, and Cockayne syndrome. The unifying feature of these conditions is exaggerated sensitivity to sunlight and UV radiation. In contrast to patients with xeroderma pigmentosum, no increase of skin cancers in patients with TTD has been observed. Genetically, 3 complementation groups have been characterized among photosensitive patients with TTD. Most patients exhibit mutations on the two alleles of the XPD gene. Rarely, mutated XPB gene or an unidentified TTD-A gene may result in TTD. In UV-sensitive TTD, the TFIIH transcription factor containing XPB and XPD helicase activities necessary for both transcription initiation and DNA repair is damaged. Beyond deficiency in the NER pathway, it is hypothesized that basal transcription may be altered leading to decreased transcription of specific genes. Depressed RNA synthesis may account for some clinical features, such as growth retardation, neurologic abnormalities, and brittle hair and nails. Therefore the attenuated expression of some proteins in differentiated cells is most likely explained by a mechanism distinct from DNA repair deficiency. The first transgenic mouse models for NER deficiencies have been generated. The TTD mouse as well as related cell models will provide important tools to understand the complex relationships between defects in DNA repair, low-sulfur hair shaft disorders, and the genotype-phenotype correlates for this constellation of inherited disorders, including the lack of predisposition to cancer in patients with TTD.

Congenital cataract and multisystem disorders

A knowledge of those syndromes associated with congenital cataract is essential for the paediatric ophthalmologist, as congenital cataracts are manifest in a large number of syndromes. It is important to have the correct diagnosis in such cases, not only for genetic and prognostic information, but also in order to help the parents to understand their child's condition. This paper describes the more common syndromes seen in association with congenital cataract, and emphasises the importance of looking at the whole child and family. We aim to provide a practical clinical guide to the diagnosis of hereditary and non-hereditary syndromes associated with congenital cataract.

Gray matter heterotopia and acute necrotizing encephalopathy in trichothiodystrophy

Trichothiodystrophy was diagnosed in a 3-year-old male presenting with speech delay, brittle hair, chronic neutropenia, and a history of febrile convulsions. Cranial magnetic resonance imaging revealed a focal subcortical and periventricular gray matter heterotopia. An acute encephalopathy with status epilepticus and coma occurred when he was 4 years of age during an upper respiratory tract infection. Magnetic resonance imaging revealed multifocal T2-weighted hypersignal lesions involving mainly the thalami, hippocampi, midbrain, and pons. Analysis of cerebrospinal fluid revealed hyperproteinorachia without pleocytosis. Results of an extensive metabolic evaluation of this acute brain injury, resembling the syndrome of acute necrotizing encephalopathy of childhood described in Japan, were negative. Focal neuronal migration disorder and acute encephalopathy with symmetric thalamic involvement are newly described neurologic manifestations of syndromes with trichothiodystrophy, which suggests that these conditions may have a common genetic background.

Trichothiodystrophy: clinical spectrum, central nervous system imaging, and biochemical characterization of two siblings

Trichothiodystrophy (TTD), an autosomal recessive disorder characterized by sulfur-deficient brittle hair, identifies a group of genetic disorders with an altered synthesis of high-sulfur matrix proteins and a defect in excision repair of ultraviolet damage in fibroblasts of most TTD patients. In contrast to patients with xeroderma pigmentosum (XP), TTD patients do not have an increased frequency of skin cancers. TTD patients may be grouped into four categories: 1) those without photosensitivity and without a defect in excision repair of UV damage; 2) those without photosensitivity and with an excision-repair defect in the same gene as in XP-D (complementation group D); 3) those with photosensitivity and with the XP-D repair defect; 4) those with photosensitivity and with a repair defect distinct from that in XP-D. We present a brother and sister in the third category of TTD. Clinically, the patients have brittle hair, short stature, ichthyosis, photosensitivity, nail and dental dysplasias, cataracts, mental retardation, and pyramidal tract abnormalities. Diagnosis was made by hair mount, which shows the characteristic banding pattern with polarizing microscopy, and by hair amino acid analysis, which demonstrated decreased high-sulfur matrix proteins. Fibroblasts cultured from skin biopsies had a marked DNA excision repair defect similar to the repair defect seen in XP-D. We have documented a unique dysmyelinating disorder on magnetic resonance imaging of the brain that might explain their mental retardation, marked hyperactivity, and neurologic deficits. Following the discovery that the human excision repair cross complementing rodent ultraviolet group 2 (ERCC2) gene is able to correct the ultraviolet sensitivity of XP-D cell strains, the ERCC2 cDNA from previous TTD patients was sequenced and shows frameshifts, deletions and point mutations in the ERCC2 gene. Molecular analysis of our patients is in progress. Molecular analysis of the defects in ERCC2 in clinically distinct patients with XP,XP/Cockayne's syndrome, and TTD may provide insight into the molecular mechanisms of these genetically related but clinically distinct disorders.