Autosomal recessive congenital ichthyosis (ARCI) presents a variety of phenotypes, included harlequin ichthyosis (HI), lamellar ichthyosis, and congenital ichthyosiform erythroderma. The clinical severity of ARCI varies significantly. HI is rare with an incidence of 1 in 300 000 live births, but it is the most severe and is often a fatal form of ARCI.1 It manifests as severely keratinized skin, widespread fissures, a harlequin face (severe ectropion, eclabium, a flattened nose, and dysplasia of the ears). Newborns face life-threatening complications including respiratory failure, hypernatremic dehydration (serum sodium concentrations of more than 150 mmol/L), electrolyte imbalance, impaired temperature regulation, and sepsis caused by various infections. A survival rate of 56% has been reported, but in recent years, this rate can be increased by improved neonatal intensive care and medical treatments.2 The ages of the survivors range from 10 months to 25 years, but the survivors still suffer with varying severity of chronic skin diseases throughout their lives.3 Multi-center data reveal that over 93% of HI cases are associate with pathogenic mutations in the ABCA12 gene (adenosine triphosphate binding cassette transporter, subfamily A, member 12), which is located on chromosome 2q33-q35.4,5
Prenatal diagnosis of HI consists of ultrasound examination for the typical morphology abnormalities, either chorionic villus biopsy or amniotic fluid sample for ABCA12 pathogenic mutations testing. A confirmed prenatal diagnosis is critical for perinatal and postnatal management, as well as genetic counseling. But only a few of cases of fetal HI have been documented. Prenatal diagnosis is unlikely to be warranted especially when the couple have no history of the disease. Here we report a case of HI diagnosed during the second-trimester of pregnancy by ultrasound scan, genetic diagnosis reveal two novel heterozygous ABCA12 mutations c.2563-2570delinsGGCAATT, p.(Leu855Glyfs∗13), and c.6116delT, p.(Met2039Argfs∗8) by the next-generation DNA sequencing (NGS). Parental consents were obtained for publication of the clinical histories of the children and pictures.
A 32-year-old, gravida-2-para-0 woman was referred to our fetal medical center at 25 weeks of gestation due to identification of fetal facial abnormalities by sonography at another hospital. Two years previously, she had a termination of pregnancy due to face and limbs malformations of the fetus although these structural abnormalities were not described clearly. The couple and the abnormal fetus did not undergo any further genetic tests. The couple were of normal appearance, and did not have a consanguineous marriage, and had no recorded family history of any inherited skin disorders. For this pregnancy, the ultrasound scan showed: a flattened face with a plane nose, the lips were thickened with the mouth being fixed and open (often described as “a fish mouth”), the mandible was retrograde, the hands and toes were abnormally fixed with hydroderma (Fig. 1).
After counseling, the couple opted for termination of pregnancy. The gross presented thickened and widespread keratinized skin, there was a thick large fissures at the neck and extending deep into the dermis, palpebral edema and ectropion, eclabium with a fixed and wide-open mouth, flat nose, micrognathia, limbs, and digits were in presence of abnormal posture and with obvious edema, scant hair, externalia hypoplastic (Fig. 2).
Umbilical cord blood and the parents’ peripheral blood were taken for whole exome sequencing. Genetic diagnosis was performed by NGS. Genomic DNA was extracted from the blood samples following the manufacturer's protocols (MagPure Buffy Coat DNA Midi KF Kit). The target resequencing library was then sequenced on MGISEQ-2000. Clinically relevant mutations were filtered and annotated based on database of NCBI dbSNP, HapMap, 1 000 human genome dataset, database of 1 000 Chinese healthy adults. Sanger sequencing was performed to verify the mutations detected in the ABCA12 gene by NGS. Primers were designed at the target sites (Exon 19: F: 5′-GAATACGGAAAGTTACCCCCTT-3′; R: 5′-GAACTTGACCCTATGAAAGCTG-3′. Exon 41: F: 5′-CTCTGTAACCGTTGGAGACC-3′; R: 5′-CCACTGGATGAAGATAAGCC-3′). A compound heterozygote of two ABCA12 mutations were identified in the fetal gene (reference: NM 173076.2), c.2563-2570delinsGGCAATT, p.(Leu855Glyfs∗13) in exon 19 and c.6116del T, p.(Met2039Argfs∗8) in exon 41. Genetic diagnosis of the parents reveal that the father is carrier of the ABCA12 c.6116delT mutation, and the mother is carrier of the ABCA12 c.2563-2570delins GGCAATT mutation (Fig. 3). The ABCA12 mutations c.2563-2570delinsGGCAATT and c.6116delT have not been described before, those two variants were both frameshift mutations, that will cause the premature termination of amino acid coding and the production of truncated proteins.
Based on clinical manifestations and the results of family genetic diagnosis, we classified the mutations in ABCA12: c.2563-2570delinsGGCAATT, p.(Leu855Glyfs∗13) and c.6116delT, p.(Met2039Argfs∗8) are both likely pathogenic mutations according to the American College of Medical Genetics and Genomics guidelines.
HI is a serious, rare, and even fatal skin disease, with a wide range of complications, and the first description of HI was made in 1750. The clinical feature of HI is diffuse hyperkeratosis skin and loss of the protective skin barrier. Cornification of the skin normally begins between 14 and 16 week gestation. The skin lesions is present as earlier as in the second-trimester of pregnancy, this makes the possibility of prenatal diagnosis of HI by ultrasonography.
Ultrasound examination, especially three-dimensional ultrasonography can now show the typical fetal facial lesions and are more intuitive and vivid than previously.6 The ultrasound morphology features of HI include: a fish-like mouth (mouth persistently opened with eversion of lips), eversion of the eyelids, a collapsed nose, dysplasia of the nostril and ears as well as abnormally fixed limb. Other ultrasound findings include microcephalus, polyhydramnios, echogenic amniotic fluid, subcutaneous edema, a short umbilical cord, macroglossia, club feet and developmental delay.7 The skin lesions become more typical as the gestational weeks increase. Some of the characteristic features will only become apparent in the late second-trimester or even third-trimester of pregnancy, when the restricted skin development becomes a limitation to fetal growth and movements. Rathore et al. reported a HI fetus although the morphology scan was unremarkable at 20 weeks of gestation. But abnormal facial features, incurved toes, clenched fists, and polyhydramnios were present at 26 weeks.8 Hence, for high-risk pregnant women, it is necessarily to perform a series of ultrasound scans in the middle and late pregnancy in order to find any HI manifestations or other structural abnormalities. A single ultrasound examination cannot completely exclude HI as a potential diagnosis. However, without suspicions for HI, prenatal diagnosis in low risk pregnancies is extremely difficult. Till now, most reported cases are diagnosed in late pregnancy. Unfortunately, fetal facial and limb morphologic abnormalities may unable to expose completely because of the influences of gestational age, fetal position and maternal obesity, that will lead low-risk cases to be missed. A detail information about the family history and previously affected children is very important to prenatal diagnose of HI.
Full-length ABCA12 protein comprises 2 595 amino acids, consists in 12 hydrophobic transmembrane domains and two cytoplasmic adenosine triphosphate binding cassette domains. The functions of ABCA12 is to transport lipid glucosylceramides to the extracellular space through lamellar granules, those are required for desquamation and keeping the skin barrier permeable. The pathogenic mutation of ABCA12 gene leads to hyperkeratosis and abnormal barrier function. Mutations in ABCA12 have been described in ARCI, including HI, congenital ichthyosiform erythroderma, and lamellar ichthyosis. HI shows the most severe phenotype. Almost all HI cases are associated with the ABCA12 mutations. As previously reported, the majority of pathogenic variants associated with HI are homozygous or compound heterozygous nonsense and frameshift substitutions, which are predicted to cause a truncated protein, resulting in severe loss of ABCA12 function. However, the genotype/phenotype correlation of HI with ABCA12 mutations is controversial. According to Rajpopat et al., mutations analysis of ABCA12 revealed that 52% of HI survivors had compound heterozygous mutations, whereas all deaths were associated with homozygous mutations. Individuals homozygous for a detrimental loss-of-function allele had the most severe and fatal course of HI. Those who were compound heterozygous were less severely.3 However, Follmann J et al. concluded the clinical outcome of HI correlates only with the residual function of the protein, not with homozygosity or compound heterozygosity, the presence of a residual protein function usually causes a less severe ARCI. They found compound mutations, c.1857delA, p.(Lys619∗), and c.5653-5655delTAT, p.(1885delTyr) in ABCA12 gene. The tyrosine at position 1885 is perfectly conserved among vertebrates and the nontruncating mutation delTyr at position 1885 probably a pathogenic variation.9 On the other hand, the severity of HI is also associated with the differential expression of the ABCA12 mutant protein. Washio K et al. reported a case of HI with the differential expression of alternatively spliced mutant transcripts of ABCA12 who showed favorable prognosis. In this study, two novel skipping mutations were identified, c.5884+4_+5delAA in exon 39 and c.7239G>A in exon 48, and the transcripts with exon 48 skipping were dominantly expressed in the skin.10 In our report, the two novel mutations c.2563–2570delinsGGCAATT and c.6116delT may cause the truncated proteins and result in severe loss of ABCA12 function. This couple are both heterozygote carriers and have a 25% risk of HI recurrence in each pregnancy. Next pregnancy, the best choice is vitro fertilization and preimplantation genetic diagnosis.
In summary, HI is a fatal and rare autosomal recessive genetic disease, multidisciplinary team management is recommended for the prenatal diagnosis. A history of affected children, family history of skin disease and screening of pathogenic genes of both parents and proband are crucial for prenatal diagnosis. Series of ultrasonic examinations should be done, no matter the pregnancy with low risk or high risk of HI. Pay attention to the scan of fetal face and limbs, especially in late pregnancy. Genetic diagnosis is critical for genetic counseling.
Cultivating funding of the First Affiliated Hospital of Chongqing Medical University (PYJJ2017-33).
All authors have been involved in the multidisciplinary diagnostic and therapeutic approach and in writing the manuscript. Professor Junnan Li read and approved the final manuscript.
Conflicts of Interest
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