Mortality-associated immunological abnormalities in trichothiodystrophy: correlation of reduced levels of immunoglobulin and neutrophils with poor patient survival

Trichothiodystrophy (TTD) is a rare, autosomal recessive disease characterized by a low content of sulphur-rich proteins in hair (Liang et al, 2006; DiGiovanna & Kraemer, 2012). Causative mutations described for TTD have been found in the genes ERCC2 (previously termed XPD), ERCC3 (also termed XPB), and GTF2H5 (subunits of the TFIIH basal transcription factor complex involved in transcription and nucleotide excision repair; also termed TTDA), GTF2E2 (a subunit of the TFIIE transcription factor complex that recruits TFIIH to the RNA polymerase II transcription initiation complex) and MPLKIP (M-phase specific PLK1 interacting protein; also termed TTDN1) (Kuschal et al, 2016).

A review of 112 published case reports of TTD described multi-system developmental abnormalities including low birth weight, short stature, microcephaly, infantile cataracts, reduced brain myelin, developmental delay, skeletal abnormalities, ichthyosis and maternal pregnancy complications (Faghri et al, 2008). TTD patients characteristically have short, brittle, sulphur-deficient hair with alternating light and dark ‘tiger-tail’ bands under polarized light microscopy (Liang, et al 2006).

Reported haematological abnormalities included microcytosis, anaemia, and elevated haemoglobin A2 (Viprakasit et al, 2001). Neutropenia was reported in 9% of the 112 cases. Hypogammaglobulinaemia in two patients was treated with immunoglobulins (Baden & Katz, 1988; Racioppi et al, 2001). Recurrent infections were present in 35% of the 112 cases. They had early mortality with a 20-fold increased risk of death before the age of 10 years. Further, 65% of the deaths were caused by infection (pneumonia or sepsis) (Faghri et al, 2008). We sought to characterize the haematological parameters, including severity of hypogammaglobulinaemia and neutropenia, in TTD patients and investigate their association with early mortality.

We performed a retrospective cohort study of 40 TTD patients (2–36 years of age, 22 males and 18 females) examined at the National Institutes of Health (NIH) from 2001 to 2017. Patients were referred by outside health care providers and enrolled in National Cancer Institute institutional review board-approved protocols. Appropriate written informed consent was obtained from all adult subjects and parents of minors. All patients were evaluated by NIH physicians and met the criteria for diagnosis of TTD (Faghri et al, 2008). All TTD patients with blood testing between 1 January 2001 and 31 December 2017 were included.

We identified 25 TTD patients with mutations in ERCC2, 5 in MPLKIP, 3 in GTF2H5, 1 in GTF2E2, and 6 unknown (Table I). Complete blood counts, reticulocyte count, quantitative immunoglobulin panel and age at death were compared using hierarchical clustering as previously described (Scheibye-Knudsen et al, 2013) (Figure S1). Suggested associations included clusters of patients with ERCC2 mutation and neutropenia and/or hypogammaglobulinaemia (Figure S1- rectangles). We further analysed the overall survival of patients with mutations in the ERCC2 gene compared with the remaining patients harbouring mutations in other known and unknown genes. As shown in Kaplan-Meier estimates (Fig 1A), the median survival of 25 TTD patients with ERCC2 mutation was 15 years (8 deaths), significantly lower than 15 patients with mutations in GTF2H5, MPLKIP, GTF2E2 or unknown genes with median survival of 36 years (2 deaths) (P = 0·04). Infection or sepsis was determined to be the cause of death in 7 of the 10 TTD patients who died. The mutated gene was ERCC2 in 6 out of 7 of these patients and was not known in 1 patient. Among these 6 ERCC2 patients, 5 were hospitalized for several months at a time for infection and died with multiple organ failure.

Table I.

Numbers of patients with different ranges of immunoglobulin levels and neutrophil counts arrayed according to underlying mutated gene^*.

		IgG level (g/l)**			ANC (×109/l)***
Gene	Total	0–5·00	5·00–6·42	>6·42	0–0·5	0·5–1·0	1·0–1·5	>1·5	IgG <5·00 g/l and ANC <0·5 × 109/l
ERCC2	25	5	7	13	6	7	6	5	2
MPLKIP	5	0	0	5	0	1	0	4	0
GTF2H5	3	0	0	3	0	0	0	3	0
GTF2E2	1	0	0	1	0	0	1	0	0
Unknown	6	1	0	5	2	1	0	3	0
Total	40	6	7	27	8	9	7	15	2

ANC, absolute neutrophil count; IgG, immunoglobulin G.

^*Patient’s values placed in bin based on lowest observed value.

^**Normal IgG values range varies with age, generally from 6·85 (4·24–10·51) g/l at 2 years of age to 9·94 (6·39–13·49) g/l in adults (Table 15–3, Hughes & Kahl, 2018).

^***Normal ANC values range varies with age, generally from 3·5 (1·5–8·5) × 10⁹/l at 2 years of age to 4·4 (1·8–7·7) × 10⁹/l in adults (Table 14–6, Hughes & Kahl, 2018).

Fig 1.

Survival of patients with Trichothiodystrophy (TTD). (A) Decreased survival of patients with ERCC2 mutation compared to patients with mutations in GTF2H5, MPLKIP, GTF2E2, and patients where mutations in known genes have not been found. Kaplan-Meier survival estimates for patients with ERCC2 mutations (n = 25, median survival 15·0 years) compared to other TTD-causing genes (n = 15, median survival 36·0 years) are shown, P = 0·04. (B) Decreased survival of TTD patients with hypogammaglobulinaemia. Kaplan-Meier survival estimates for patients with IgG level ≤5·0 g/l (n = 6, median survival 3·7 years) compared to IgG > 5·0 g/l (n = 34, median survival 36·0 years) are shown, P < 0·002. (C) Survival of TTD patients with severe neutropenia. Kaplan-Meier survival estimates for patients for an absolute neutrophil count (ANC) ≤1·0 × 10⁹/l (n = 17) compared to ANC > 1·0 × 10⁹/l (n = 22) are shown, P value was not significant (NS). (D) Survival of TTD patients with anaemia (defined in Table 14–1 Hughes, H.K., Lauren 2018). Kaplan-Meier survival estimates for anaemic patients (n = 8) compared to non-anaemic patients (n = 32), P value was not significant. Statistical testing was performed using Gehan-Breslow-Wilcoxon tests.

Hypogammaglobulinaemia was associated with early mortality in TTD patients (Fig 1B). Thirteen patients had an IgG level below the age-adjusted lower limit of normal. Twelve of these patients had a mutation in ERCC2. Multiple IgG laboratory values were available on 8 of these patients. IgG was low on more than one test in 4 patients. The lowest IgG in the entire study of 40 patients was 2·69 g/l. The group of 6 patients in the cohort with IgG level below 5·0 g/l had an increased mortality compared to the remaining group of 34 patients with IgG level > below 5·0 g/l (Fig 1B, median survival 3·7 vs. 36 years, P = 0·002). These six patients ranged in age from 2 to 17 years and all had IgG levels below age-adjusted standards (Table I and Figure S1) (Hughes & Kahl, 2018).

Neutropenia was common in TTD patients, and the lowest observed absolute neutrophil count (ANC) was 0·23 × 10⁹/l (Fig 1C). Seventeen patients had an ANC below 1·0 × 10⁹/l, of which 13 had ERCC2 mutations. Eight of these patients had an ANC below 0·5 × 10⁹/l, of which 6 had ERCC2 mutations and 2 others had mutations in unknown genes (Table I and Figure S1). Laboratory results from more than one clinic visit were available for 19 patients, and among this group, 10 patients had an ANC less than 1·0 × 10⁹/l on more than one occasion, and one patient had an ANC below 0·5 × 10⁹/l on more than one occasion. There was a non-significant trend towards decreased survival in TTD patients with ANC less than 1·0 × 10⁹/l when compared to the remaining patients.

Mild anaemia was present in 8 patients, with the lowest haemoglobin being 100 g/l (Fig 1D). All patients with anaemia had microcytosis, low iron saturation and normal ferritin (Figure S1). Significant microcytosis with mean corpuscular volume (MCV) below 70 fl was present in 7 patients, and the lowest MCV was 55·9 fl. Mutated genes identified in patients with anaemia were ERCC2 (6), GTF2H5 (1) and unknown (1). Among all patients with TTD, low iron saturation was prevalent (60%, 24 patients), as well as microcytosis (38%, 15 patients). Survival of the 8 patients with anaemia was not significantly different from the other 32 patients (Fig 1D).

Based on observed early mortality in our cohort, we propose surveillance of TTD patients for recurrent infections, hypogammaglobulinaemia and neutropenia. Haematological evaluation may be considered for the management of hypogammaglobulinaemia or neutropenia with supplemental immunoglobulins or granulocyte colony-stimulating factor, respectively.

Supplementary Material

Figure S1.

Hierarchical cluster representing TTD patient’s mutations and laboratory results.