Trichothiodystrophy with sideroblastic anaemia and developmental delay

Mitral regurgitation as a phenotypic manifestation of nonphotosensitive trichothiodystrophy due to a splice variant in MPLKIP

Background

Nonphotosensitive trichothiodystrophy (TTDN) is a rare autosomal recessive disorder of neuroectodermal origin. The condition is marked by hair abnormalities, intellectual impairment, nail dystrophies and susceptibility to infections but with no UV sensitivity.

Methods

We identified three consanguineous Pakistani families with varied TTDN features and used homozygosity mapping, linkage analysis, and Sanger and exome sequencing in order to identify pathogenic variants. Haplotype analysis was performed and haplotype age estimated. A splicing assay was used to validate the effect of the MPLKIP splice variant on expression.

Results

Affected individuals from all families exhibit several TTDN features along with a heart-specific feature, i.e. mitral regurgitation. Exome sequencing in the probands from families ED168 and ED241 identified a homozygous splice mutation c.339 + 1G > A within MPLKIP. The same splice variant co-segregates with TTDN in a third family ED210. The MPLKIP splice variant was not found in public databases, e.g. the Exome Aggregation Consortium, and in unrelated Pakistani controls. Functional analysis of the splice variant confirmed intron retention, which leads to protein truncation and loss of a phosphorylation site. Haplotype analysis identified a 585.1-kb haplotype which includes the MPLKIP variant, supporting the existence of a founder haplotype that is estimated to be 25,900 years old.

Conclusion

This study extends the allelic and phenotypic spectra of MPLKIP-related TTDN, to include a splice variant that causes cardiomyopathy as part of the TTDN phenotype.

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.

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.