Cerebro-oculo-facio-skeletal syndrome with a nucleotide excision-repair defect and a mutated XPD gene, with prenatal diagnosis in a triplet pregnancy

Abstract

Cerebro-oculo-facio-skeletal (COFS) syndrome is a recessively inherited rapidly progressive neurologic disorder leading to brain atrophy, with calcifications, cataracts, microcornea, optic atrophy, progressive joint contractures, and growth failure. Cockayne syndrome (CS) is a recessively inherited neurodegenerative disorder characterized by low to normal birth weight, growth failure, brain dysmyelination with calcium deposits, cutaneous photosensitivity, pigmentary retinopathy and/or cataracts, and sensorineural hearing loss. Cultured CS cells are hypersensitive to UV radiation, because of impaired nucleotide-excision repair (NER) of UV-induced damage in actively transcribed DNA, whereas global genome NER is unaffected. The abnormalities in CS are caused by mutated CSA or CSB genes. Another class of patients with CS symptoms have mutations in the XPB, XPD, or XPG genes, which result in UV hypersensitivity as well as defective global NER; such patients may concurrently have clinical features of another NER syndrome, xeroderma pigmentosum (XP). Clinically observed similarities between COFS syndrome and CS have been followed by discoveries of cases of COFS syndrome that are associated with mutations in the XPG and CSB genes. Here we report the first involvement of the XPD gene in a new case of UV-sensitive COFS syndrome, with heterozygous substitutions-a R616W null mutation (previously seen in patients in XP complementation group D) and a unique D681N mutation-demonstrating that a third gene can be involved in COFS syndrome. We propose that COFS syndrome be included within the already known spectrum of NER disorders: XP, CS, and trichothiodystrophy. We predict that future patients with COFS syndrome will be found to have mutations in the CSA or XPB genes, and we document successful use of DNA repair for prenatal diagnosis in triplet and singleton pregnancies at risk for COFS syndrome. This result strongly underlines the need for screening of patients with COFS syndrome, for either UV sensitivity or DNA-repair abnormalities.

Figure 1

Clinical appearance of patient with COFS syndrome. Patient is shown at age 3 wk (left) and at age 9 mo (right).

Figure 2

DNA-repair characteristics of patient's fibroblasts (black symbols) and of normal C5RO cells (white symbols). Standard-error bars are shown wherever they exceed symbol size. A, UV-survival curves, compared to typical XP-A and XP-C strains measured in a separate experiment. B, GG-NER activity in mononuclear cells of patient (black bars) mononuclear cells from fusion partner (representative of XP group B, D, or G) (white bars), and heterokaryons in fusion experiments (gray bars), measured as UDS and represented as a percentage of that in normal C5RO cells tested in the same experiment. C, Residual rates of overall DNA synthesis 16 h after exposure to various UV doses. Typical responses of XP-A and CS-B cells are from a separate experiment.

Figure 3

Molecular genetic analysis of XPD gene. A, Restriction-enzyme fingerprinting of 3′ cDNA fragment 4 (shown in panel D), digested with RsaI-HhaI. Red arrows indicate new bands appearing in patient's DNA (lane P), compared to normal sequence (lane N). B, Relevant parts of XPD sequence readout. Both mutations found were heterozygous. C, Conservation of XPD amino acids around mutation D681N. Rodent = Mus musculus and Cricetulus griseus; fish = Xiphophorous maculatus. D, Bar representation of XPD protein with seven helicase domains, mutations found in the proband (black) and in two other patients in XP-D who have symptoms of CS (gray) (from Lehmann 2001).