The skin microbiome in X-linked recessive ichthyosis and autosomal recessive congenital ichthyosis

Ichthyosis is a group of hereditary, chronic skin diseases in which the
keratinization process of the skin is disturbed. These can be classified as
ichthyosis vulgaris (IV), X-linked recessive ichthyosis (XRI), autosomal
recessive congenital ichthyosis (ARCI), epidermolytic ichthyosis (EI) and
syndromic ichthyosis. In the group of ARCI, patients are also traditionally
subdivided by clinical phenotype, namely lamellar ichthyosis (LI; generalized,
thick, brown flakes), congenital ichthyosiform erythroderma (CIE; generalized
erythema with fine white flakes) and the rare harlequin ichthyosis (premature
neonate with very rigid collodion membrane, high risk of complications and
mortality).
The treatment options for ichthyosis are limited and often insufficiently
effective (Mazereeuw-Hautier et al., 2019). Quality of life depends on disease
severity, which can vary from mild to severe in IV and XRI and from moderate to
severe in ARCI. Studies show that all forms of ichthyosis give a clearly
decreased quality of life (Troiano et al., 2020).
The pathophysiology of ichthyosis has not yet been fully elucidated. All forms
of ichthyosis lead to abnormal epidermal differentiation and desquamation of
the skin. Atopic eczema (AE) is strongly associated with IV, the most common
form of ichthyosis (Oji et al., 2010). The Th2 axis plays an important role in
AE, with IL-4 and IL-13 dominating the inflammatory profile. Initial research
results on other variants of ichthyosis show an IL-17 predominant immune
profile (Paller et al., 2010; Czarnowicki et al., 2018).
In common skin diseases, skin microbiota, and in particular changes in their
composition (i.e.: dysbiosis), have been associated with the pathogenesis of
these diseases. This dysbiosis can be the result of a changed bacterial
composition, a disturbed immune response to them, or both. This could be a
driving factor in inflammatory skin diseases such as AE and psoriasis (Zeeuwen
et al., 2013). However, research results on the skin microbiome of psoriasis
patients are contradictory and have not led to identification of a
psoriasis-specific microbiome (Alekseyenko et al., 2013; Assarsson et al.,
2018; Fahlen et al., 2012; Gao et al., 2008; Loesche et al., 2018; Tett et al.,
2017).
In the case of AE, clear differences are found in the skin microbiome compared
to healthy volunteers, namely decrease in microbial diversity, decrease in
commensal bacteria and overgrowth of Staphylococcus aureus (Fyhrquist et al.,
2019; Kong et al., 2012). However, it is still unclear whether this dysbiosis
of the skin microbiome leads to disease, or whether the changed skin conditions
(lesions) are the cause of the changed microbiota composition of the skin.
Influencing the skin microbiome in patients with AE can lead to an improvement
of the disease severity. It has been reported that treatment with diluted
bleaching baths in these patients inhibits the colonization of Staphylococcus
aureus and reduces the severity of AE (Huang et al., 2009). Furthermore, use of
corticosteroids and immunosuppressants has been shown to reduce the dermatitis
and Staphylococcus aureus colonization in AE (Gonzalez et al., 2016; Hung et
al., 2007). Recently, it has been found that treatment with coal tar leads to a
decrease in the amount of Staphylococcus species and an increase in the amount
of Cutibacterium species, indicating a shift in microbiota composition towards
healthy controls (Smits et al., 2020). In vivo modulation of cutaneous
microbiota through skin microbiota transplantation and topical application of
pre- and probiotics is also finding its way into research applications (Myles
et al., 2018).
With respect to ichthyosis, only one study in human subjects has been published
so far. It showed that filaggrin deficiency affects the microbiota composition
of non-eczematous skin in IV patients compared to healthy controls. In
particular, IV skin displayed a reduced amount of Gram-positive anaerobic cocci
(GPAC) (Zeeuwen et al., 2017). In the current project we aim to complement the
knowledge of the skin microbiome in XRI and ARCI patients, and possibly also
create a new therapeutic entrance.

Primary Objective:
Our main objective is to analyse if the microbiota composition of the affected
skin is different from the non-affected skin in XRI and ARCI.

Secondary Objectives:
(1) To investigate the composition of the skin microbiota of patients with XRI
and ARCI and to investigate whether we can make a distinction between the
different clinical phenotypes of ARCI based on the skin microbiota composition.

(2) To compare the microbiota composition of XRI and ARCI patients with
(already existing data of) healthy individuals and patients with AE and/or IV.

(3) For future follow-up studies regarding the pathogenesis of ichthyosis, we
want to explore if specific clinical XRI and ARCI bacterial isolates can be
identified.

We will perform an transverse study with an exploratory character on a
population of patients with XRI and ARCI. Expected study duration is 24 months
and it will be performed in the Maastricht University Medical Center+.
Initially, we will study photo documentation of 20 XRI and 20 ARCI patients
from the MUMC+ database to identify the most and least affected skin locations.
For each patient, we will assess anatomical locations such as lower leg, thigh,
etc, using the investigator global assessment score (0-4) (Vahlquist et al.,
2013) and in this way select the average most and least affected area in this
patient group. The sampling site is thus made uniform for all patients.Two
samples will be taken from the most affected skin site and two samples of the
least affected skin site in these patients, i.e. 4 samples per patient, in a
total of 60 patients. From every skin location one sample is used for
microbiota analysis (V3-V4 16S rRNA marker gene Illumina Sequencing). This will
create insight into the bacterial taxa and their relative abundance. The other
sample is used for bacterial culture on blood agar plates under aerobic and
anaerobic conditions. Bacterial colonies will be selected (on morphology,
color, size) and stored at -80°C for future experiments.

The procedure will be a swab of the skin. This will only touch the skin and
will not hurt or penetrate the skin any deeper. This will have minimal to no
risks for the patient. Furthermore, the procedure will take place during a
regular clinic visit, so there is no additional time burden.