Report of a Novel ALOX12B Mutation in Self-Improving Collodion Ichthyosis with an Overview of the Genetic Background of the Collodion Baby Phenotype

Collodion baby is a congenital, transient phenotype encountered in approximately 70–90% of autosomal recessive congenital ichthyosis and is an important entity of neonatal erythroderma. The clinical outcome after this severe condition is variable. Genetic mutations of components of the epidermal lipoxygenase pathway have been implicated in the majority of self-improving collodion ichthyosis (SICI). In SICI, the shedding of the collodion membrane reveals clear skin or only mild residual manifestation of ichthyosis. Here we report the case of a girl born with a severe form of collodion baby phenotype, whose skin almost completely cleared within the first month of life. At the age of 3 years, only mild symptoms of a keratinization disorder remained. However, the severity of erythema and scaling showed mild fluctuations over time. To objectively evaluate the skin changes of the patient, we assessed the ichthyosis severity index. Upon sequencing of the ALOX12B gene, we identified a previously unreported heterozygous nonsense mutation, c.1607G>A (p.Trp536Ter) with the recurrent, heterozygous mutation c.1562A>G (p.Tyr521Cys). Thereby, our findings expand the genotypic spectrum of SICI. In addition, we summarize the spectrum of further genetic diseases that can present at birth as collodion baby, in particular the SICI.


Introduction
Autosomal recessive congenital ichthyosis (ARCI) is a major subgroup of the nonsyndromic forms of congenital ichthyosis characterized by abnormal skin cornification with hyperkeratosis, diffuse scaling and variable degree of erythroderma. ARCI is a rare condition, the reported prevalence varies between 1:33,000 and 1:300,000 [1][2][3]. ARCI has diverse clinical manifestations. To date, the mutational spectrum encompasses ten genes that encode proteins (enzymes, transport proteins) responsible for the formation of the stratum corneum [4,5]. Subtypes of ARCI traditionally include lamellar ichthyosis (LI) Life 2021, 11, 624 2 of 12 with large, dark, plate-like scales without erythroderma, and congenital ichthyosiform erythroderma (CIE) with generalized fine scaling and erythroderma. Although LI and CIE are considered two distinct clinical entities, patients often show overlapping features [6]. The most severe subtype of ARCI is Harlequin ichthyosis (HI), which is triggered by inactivating mutations of the ABCA12 gene [7,8]. About 70-90% of ARCI newborns are born encased in a parchment-like membrane, referred to as the collodion membrane [9,10]. It is noteworthy that the prevalence might be even higher, since due to the occasionally mild clinical presentation, most of the cases may go unreported [11]. The term collodion baby (CB) refers to an early, transient phenotype, most commonly encountered in the case of ARCI, rather than a distinct disease entity of ichthyoses. In the majority of cases, the shedding of the collodion membrane is followed by the development of LI or CIE. About 10-20% of CBs show clear skin or only mild symptoms of ichthyosis later on, which was previously referred to as self-healing collodion baby (SHCB). However, the term self-improving collodion ichthyosis (SICI) is preferable instead of SHCB as this minor group of ARCI patients usually still show residue symptoms of LI or CIE. Vahlquist et al. proposed the umbrella term pleomorphic ichthyosis for cases characterized by marked skin changes at birth and subsequently mild symptoms of ichthyosis encompassing SICI, ichthyosis prematurity syndrome, bathing-suit ichthyosis and congenital ichthyosis with mild scaling [4,12]. SICI is predominantly associated with mutations in the ALOX12B, ALOXE3 and less often TGM1 genes [1,13,14]. Lately, the mutation spectrum was expanded with the CYP4F22 gene [9,14]. The severity of ichthyosis in later life in the case of CB is diverse, ranging from HI to variable degree of LI/CIE and SICI. While genetic testing is an important tool for the diagnosis of ichthyosis, the outcome of CB usually cannot be accurately predicted at birth [15]. Here, in addition to a brief review of the literature regarding the diversity of genotype-phenotype correlation of CB, we report a case of a SICI with a novel mutation of the ALOX12B gene that further expands the genotypic spectrum of SICI.

Disease Severity Assessment
We applied the disease severity score for newborns with collodion membrane of Rubio-Gomez et al. to describe the status of the newborn patient [15]. In addition, to objectively assessing the skin changes of the patient, we used the ichthyosis severity index of Marukian et al. [16]. Erythema and scaling were evaluated on the upper back region of the patient.

Mutation Analysis
Genomic DNA was isolated from peripheral blood leukocytes of the patient and her parents with a Roche MagNA Pure Compact system (Roche Diagnostics, Mannheim, Germany) or with a BioRobot EZ1 DSP Workstation (QIAGEN; Hilden, Germany), for TGM1 or ALOX12B and ALOXE3, respectively. After the amplification of the coding regions and flanking introns of the TGM1 (primer pairs for PCR were as described previously [17,18]), ALOX12B and ALOXE3 genes (using primer sequences displayed on the UCSC Genome Browser, http://www.genome.ucsc.edu, accessed on 24 April 2019), DNA sequencing was performed on amplification products. Sequencing data were analyzed in order to screen for any genetic variations.
Written informed consent was obtained from the parents of the patient, and the study was conducted according to the Principles of the Declaration of Helsinki.

Case Report
Here we report the case of a three-year-old girl, who was born to non-consanguineous parents at 37 gestational weeks following an uncomplicated pregnancy, through a normal vaginal delivery as a CB. The parents had no relevant history of skin diseases. The newborn Life 2021, 11, 624 3 of 12 was covered in an opaque membrane with underlying erythroderma ( Figure 1A-C). The intertriginous regions and the trunk presented with several fissures. Marked ectropion and eclabium could be noted as well. Routine neonatal assessment was otherwise normal with an Apgar score of 9/9 at 1 and 5 min, respectively. Due to the marked skin changes, the newborn was transferred to a perinatal intensive care unit. The skin status dynamically changed during the first few days postpartum. Due to the compression of the shiny, tight collodion membrane, the extremities appeared edematous and fingers were fixed in a contracture ( Figure 1D). Elevated inflammatory markers and positive skin and blood culture showed signs of a multimicrobial infection, which was treated successfully with combined intravenous antibiotic therapy. The newborn had severe anemia secondary to the infection, for which she received blood transfusion. Her skin improved following treatment with topical emollients; the ectropion and eclabium healed and she was emitted from the intensive care unit at the age of 18 days. By the age of one month, the shedding of the collodion membrane revealed erythroderma with fine white scaling. Over time, the severity of the erythema and scaling fluctuated ( Figure 2). Currently, at age of three, the patient has mild residual manifestation of ichthyosis, namely xerosis and mild erythematous macules.
Here we report the case of a three-year-old girl, who was born to non-cons ous parents at 37 gestational weeks following an uncomplicated pregnancy, th normal vaginal delivery as a CB. The parents had no relevant history of skin disea newborn was covered in an opaque membrane with underlying erythroderma 1A-C). The intertriginous regions and the trunk presented with several fissures. ectropion and eclabium could be noted as well. Routine neonatal assessment w wise normal with an Apgar score of 9/9 at 1 and 5 min, respectively. Due to the skin changes, the newborn was transferred to a perinatal intensive care unit. status dynamically changed during the first few days postpartum. Due to the com of the shiny, tight collodion membrane, the extremities appeared edematous and were fixed in a contracture ( Figure 1D). Elevated inflammatory markers and posi and blood culture showed signs of a multimicrobial infection, which was treated fully with combined intravenous antibiotic therapy. The newborn had severe ane ondary to the infection, for which she received blood transfusion. Her skin impro lowing treatment with topical emollients; the ectropion and eclabium healed and emitted from the intensive care unit at the age of 18 days. By the age of one mo shedding of the collodion membrane revealed erythroderma with fine white scali time, the severity of the erythema and scaling fluctuated ( Figure 2). Currently, three, the patient has mild residual manifestation of ichthyosis, namely xerosis a erythematous macules.

Disease Severity
Collodion membrane severity score was 12 points out of 15, which accounts for high severity. Changes of the ichthyosis severity index after the neonatal period, including the erythema and scaling score, are seen in Figure 3. Scaling was mild after 1 month of age, while the erythema score fluctuated during the observed time period.

Disease Severity
Collodion membrane severity score was 12 points out of 15, which accounts for high severity. Changes of the ichthyosis severity index after the neonatal period, including the erythema and scaling score, are seen in Figure 3. Scaling was mild after 1 month of age, while the erythema score fluctuated during the observed time period.

Disease Severity
Collodion membrane severity score was 12 points out of 15, which accounts f severity. Changes of the ichthyosis severity index after the neonatal period, includ erythema and scaling score, are seen in Figure 3. Scaling was mild after 1 month while the erythema score fluctuated during the observed time period.

Mutation Analysis
Sequencing of ALOX12B revealed a previously described pathogenic, missense mutation, c.1562A>G (p.Tyr521Cys) in one allele ( Figure 4) and a previously not reported, nonsense mutation c.1607G>A (p.Trp536Ter) in the other allele ( Figure 5). Thus, the patient had a compound heterozygote mutation in the ALOX12B gene.

Mutation Analysis
Sequencing of ALOX12B revealed a previously described pathogenic, missense mu tation, c.1562A>G (p.Tyr521Cys) in one allele ( Figure 4) and a previously not reported nonsense mutation c.1607G>A (p.Trp536Ter) in the other allele ( Figure 5). Thus, the pa tient had a compound heterozygote mutation in the ALOX12B gene. Upon sequencing of TGM1 and ALOXE3, wild type alleles were detected. Parenta testing revealed c.1607G>A (p.Trp536Ter) heterozygous mutation of ALOX12B in th mother and c.1562A>G (p.Tyr521Cys) heterozygous mutation of ALOX12B in the paterna sample.

Discussion
ARCI is a genetically heterogeneous group of cornification disorders with divers

Mutation Analysis
Sequencing of ALOX12B revealed a previously described pathogenic, missense mu tation, c.1562A>G (p.Tyr521Cys) in one allele ( Figure 4) and a previously not reported nonsense mutation c.1607G>A (p.Trp536Ter) in the other allele ( Figure 5). Thus, the pa tient had a compound heterozygote mutation in the ALOX12B gene. Upon sequencing of TGM1 and ALOXE3, wild type alleles were detected. Parenta testing revealed c.1607G>A (p.Trp536Ter) heterozygous mutation of ALOX12B in the mother and c.1562A>G (p.Tyr521Cys) heterozygous mutation of ALOX12B in the paterna sample.

Discussion
ARCI is a genetically heterogeneous group of cornification disorders with diverse and often dynamically changing or overlapping phenotypes. The presence of collodion Upon sequencing of TGM1 and ALOXE3, wild type alleles were detected. Parental testing revealed c.1607G>A (p.Trp536Ter) heterozygous mutation of ALOX12B in the mother and c.1562A>G (p.Tyr521Cys) heterozygous mutation of ALOX12B in the paternal sample.

Discussion
ARCI is a genetically heterogeneous group of cornification disorders with diverse and often dynamically changing or overlapping phenotypes. The presence of collodion membrane at birth is often the initial presentation of ARCI. Later, CB develops into CIE/LI or, on rare occasions, heals spontaneously. This latter phenotype is known as SICI, where patients show clear or almost clear skin with mild signs of ichthyosis.
Here we reported the case of a CB, whose symptoms improved significantly after birth. Sequencing of the ALOX12B gene revealed c.1526A>G (p.Tyr521Cys), a frequently reported, well-documented mutation and a novel, pathogenic nonsense mutation, c.1607G>A (p.Trp536Ter). Vahlquist et al. reported five SICI patients with the c.1526A>G (p.Tyr521Cys) mutation [19]. Before that, this particular mutation was only documented in case of other forms of ARCI (LI/CIE) [19]. In a new meta-analysis exploring the genotypic spectrum of ALOX12B and ALOXE3 mutations, c.1526A>G (p.Tyr521Cys) was the most frequent mutation, with an allelic frequency of 22% (61 out of 282 alleles) [5]. Although c.1526A>G (p.Tyr521Cys) frequently occurs in SICI cases, it was detected in numerous LI and CIE patients as well, both in homozygote and compound heterozygote form [5]. Based on this meta-analysis, CB phenotype was documented in 25 out of 44 cases with either heterozygous or homozygous form of c.1526A>G (p.Tyr521Cys) mutation, including five SICI cases. On the other hand, to the best of our knowledge, the other mutation of the patient, c.1607G>A (p.Trp536Ter), has not yet been reported in the literature. The novel c.1607G>A (p.Trp536Ter) mutation affects exon 12 of ALOXB12 gene and causes a premature stop codon.
Of note, in case of mutations of genes encoding the lipoxygenase enzymes, the outcome of CB cannot be accurately predicted neither based on genetic analysis nor the initial clinical presentation [5]. In addition, in our experience, the severity of the disease, e.g., the degree of erythema, can show relapses and remissions that probably are influenced by variable exogenous and endogenous factors. The background of the dramatic improvement of the skin status in SICI after birth is unknown. In the case of TGM1 mutations, two mutated alleles were found to be sensitive to hydrostatic pressure that results in inactive transglutaminase-1 enzyme in utero, which explains the severe phenotype in the newborn that later resolves in normal environmental conditions [20]. Such an explanation does not exist in the case of the lipoxygenase pathway genes. However, the fact that patients with identical mutations can demonstrate different outcomes suggests the role of yet undiscovered factors. A multicentric study confirmed a similar trend as Rubio-Gomez et al.-toward a higher collodion membrane severity score in the case of non-syndromic forms of ichthyosis compared to syndromic forms [15,21]. However, this study could not establish a strong link between the collodion membrane score and the clinical outcome of the disease. The authors hypothesized that it was due to the fact that genes that cause non-syndromic forms of ichthyosis are related to a higher differentiation state of keratinocytes. Our patient had a high ichthyosis severity score, which fits in with the trend that these two studies established. However, the outcome of the SICI phenotype could not be predicted based on this scoring system. While collodion membrane at birth occurs most commonly in ARCI, it must be noted that other diseases can present at birth as CB. These include other forms of syndromic and non-syndromic forms of ichthyosis, hypohidrotic ectodermal dysplasia, palmoplantar keratosis with leukokeratosis anogenitalis [15], congenital hypothyroidism [22,23], alpha-ketoadipic aciduria [24,25] and koraxitrachitic syndrome [26] (Tables 1 and 2).   It is important to note that while these diseases can present as CB at birth, most of them are rare exceptions in the literature. So far, two cases with congenital hypothyroidism and one with alpha-ketoadipic aciduria were reported to be born as CB [22][23][24]. Although koraxitrachitic syndrome is frequently cited in association to rare causes of the CB pheno-Life 2021, 11, 624 9 of 12 type, there are very few publications about this rare entity [26]. A recent article reported the case of a Harlequin fetus-like newborn, who improved in the first weeks and presented with palmoplantar keratoderma and leukokeratosis anogenitalis caused by KDSR mutation. Autosomal recessive mutations of KDSR are the cause of erythrokeratodermia variabilis et progressiva 4 as well where a vernix-like thickened skin was documented at birth, in some cases besides a true collodion membrane [55]. Another interesting point is the difference of CB and Harlequin ichthyosis at birth. By definition, Harlequin fetus is a neonatal phenotype that later develops to the most severe form of ichthyosis. According to the First Ichthyosis Consensus Conference in Sorèze, the Harlequin fetus is a severe form of CB with thick plate-like, cornified skin [59]. However, due to the marked skin changes and different clinical consequences, it is often referred to as a distinct disease entity in the literature [10,60]. Additionally, it is important to note that there are neonatal conditions that can be confused with the CB phenotype, including ichthyosis prematurity syndrome (OMIM# 604194) and keratitis-ichthyosis-deafness syndrome (OMIM# 600157). The marked skin changes at birth resemble excessive amounts of vernix caseosa in these cases [61]. However, due to the lack of a unified nomenclature, some of these cases are reported as a collodion membrane in the literature [9].

Conclusions
In conclusion, we described the case of a SICI, where the patient had a compound heterozygous mutation in the ALOX12B gene. Here, we identified a previously unreported, pathogenic, nonsense mutation c.1607G>A (p.Trp536Ter) along with a recurrent, pathogenic, missense mutation, c.1562A>G, (p.Tyr521Cys). Our case supports the notion that the clinical interpretation and the determination of the prognosis based on genotypephenotype correlation regarding SICI is challenging. The clinical outcome of a CB cannot always be accurately predicted based on the severity of the clinical presentation at birth; thus, genetic testing is essential. However, in the case of mutations of the lipoxygenase enzyme genes, an association between specific mutations and the mature phenotype could not yet be confirmed. Thus, counseling and education of the parents are of great importance in these cases.  Informed Consent Statement: Written informed consent was obtained from the parents of the patient to participate. Patients signed informed consent regarding publishing their data.

Data Availability Statement:
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.