A novel missense mutation of the STS gene in two siblings with X-linked ichthyosis, complicated by short stature, bone density reduction, epilepsy, and cryptorchidism

Revisiting X-linked congenital ichthyosis

X-linked recessive ichthyosis (XLI) is a hereditary skin disease characterized by generalized dryness and scaling of the skin, with frequent extracutaneous manifestations. It is the second most common type of ichthyosis, with a prevalence of 1/6,000 to 1/2,000 in males and without any racial or geographical differences. The causative gene for XLI is the steroid sulfatase gene (STS), located on Xp22.3. STS deficiency causes an abnormal cholesterol sulfate (CS) accumulation in the stratum corneum (SC). Excess CS induces epidermal permeability barrier dysfunction and scaling abnormalities. This review summarizes XLI's genetic, clinical, and pathological features, pathogenesis, diagnosis and differential diagnoses, and therapeutic perspectives. Further understanding the role of the STS gene pathogenic variants in XLI may contribute to a more accurate and efficient clinical diagnosis of XLI and provide novel strategies for its treatment and prenatal diagnosis.

Identification of carrier status of Xp22.31 microdeletions associated with X-linked ichthyosis at the single-cell level using haplotype linkage analysis by karyomapping

PURPOSE

Currently, owing to the limitations of high-throughput sequencing depth and the allele dropout caused by the whole-genome amplification, detection of chromosomal variants in embryos with CNVs <5 Mb is unsatisfactory at the single-cell level using only conventional sequencing methods. Therefore, here we aimed to use a strategy of preimplantation genetic testing for monogenic (PGT-M) to compensate for the shortcomings of conventional sequencing methods. The purpose of this study is to report the effectiveness of haplotype linkage analysis by karyomapping for preimplantation diagnosis microdeletion diseases.

METHODS

Six couples carrying chromosomal microdeletions associated with X-linked ichthyosis were recruited, and all couples entered the PGT process. Multiple displacement amplification (MDA) method was used to amplify the whole-genome DNA of trophectoderm cells. Then karyomapping based on single nucleotide polymorphism (SNP) was used for haplotype linkage analysis to detect alleles carrying microdeletions, and CNVs of embryos were identified to determine euploid identity. Amniotic fluid tests were performed in the second trimester to verify the PGT-M results.

RESULTS

All couples were tested for chromosomal microdeletions, with deletion fragments ranging in size from 1.60 to 1.73 Mb, and one partner in each couple did not carry the microdeletion. Three couples successfully underwent PGT-M assisted conception and obtained healthy live births.

CONCLUSION

This study shows that haplotype linkage analysis by karyomapping could effectively detect the carrier status of embryos with microdeletions at the single-cell level. This approach may be applied to the preimplantation diagnosis of various chromosomal microvariation diseases.

X-linked ichthyosis: New insights into a multi-system disorder

Background

X-linked ichthyosis (XLI) is a rare genetic condition almostexclusively affecting males; it is characterised by abnormal desquamation and retentionhyperkeratosis, and presents with polygonal brown scales. Most cases resultfrom genetic deletions within Xp22.31 spanning the STS (steroid sulfatase)gene, with the remaining cases resulting from STS-specific mutations. For manyyears it has been recognised that individuals with XLI are at increased risk ofcryptorchidism and corneal opacities.

Methods

We discuss emerging evidence that such individuals are alsomore likely to be affected by a range of neurodevelopmental and psychiatrictraits, by cardiac arrhythmias, and by rare fibrotic and bleeding-relatedconditions. We consider candidate mechanisms that may confer elevatedlikelihood of these individual conditions, and propose a novel commonbiological risk pathway.

Results

Understanding the prevalence, nature and co-occurrence ofcomorbidities associated with XLI is critical for ensuring early identificationof symptoms and for providing the most effective genetic counselling andmultidisciplinary care for affected individuals.

Conclusion

Future work in males with XLI, and in new preclinical andcellular model systems, should further clarify underlying pathophysiologicalmechanisms amenable to therapeutic intervention.

X-Linked Familial Focal Epilepsy Associated With Xp22.31 Deletion

BACKGROUND

The genetic basis for familial focal epilepsy is poorly understood, with most of the known genetic causes occurring via autosomal dominant inheritance. X-linked familial focal epilepsy has not been previously reported.

METHODS

We reviewed our research database for cases of X-linked focal epilepsy.

RESULTS

We identified three boys with X-linked ichthyosis and focal epilepsy, including two maternal cousins. Age of seizure onset ranged from seven to 10 years, and all three patients had seizures that were relatively easily controlled. The epilepsy phenotype in all boys was consistent with self-limited focal epilepsy of childhood, most closely resembling childhood epilepsy with centrotemporal spikes. Brain magnetic resonance imaging was normal in two of the boys, with a third found to have a suspected focal cortical dysplasia. All three boys carried maternally inherited hemizygous Xp22.31 deletions (estimated size 0.9 to 1.66 Mb), affecting four to six genes. Of the affected genes, only STS has clear clinical relevance; deletions, and pathogenic variants in STS cause X-linked ichthyosis, although all patients described had only minor skin findings.

CONCLUSIONS

The findings in these patients illustrate that X-linked familial focal epilepsy can occur, although it is a rare entity. Although STS pathogenic variants are likely better categorized as an epilepsy risk factor, variants in this gene may partially explain the male predominance observed in specific epilepsy phenotypes, namely childhood epilepsy with centrotemporal spikes.

X-linked ichthyosis: Molecular findings in four pedigrees with inconspicuous clinical manifestations

Background

X‐linked ichthyosis (XLI) is the second most common type of ichthyosis, which is characterized by wide and symmetric distribution of adherent, dry, and polygonal scales on the skin. Steroid sulfatase (STS) gene, which is located at chromosome Xp22.31, has been identified as the pathogenic gene of XLI.

Methods

In this study, chromosome karyotype analysis, bacterial artificial chromosomes‐on‐Beads™ (BoBs) assay, fluorescence in situ hybridization (FISH), and single nucleotide polymorphism array (SNP‐array) were employed for the prenatal diagnoses in three pregnant women with high‐risk serological screening results and a pregnant woman with mental retardation.

Results

STS deletion was identified at chromosome Xp22.31 in all four fetuses. Postnatal follow‐up confirmed the diagnosis of ichthyosis in two male fetuses and revealed normal dermatological manifestations in other two female fetuses carrying ichthyosis.

Conclusion

The results of the present study demonstrate that a combination of karyotypying, prenatal BoBs, FISH, and SNP‐array may avoid the missed detection of common microdeletions and ensure the accuracy of the detection results, which provides a feasible tool for the reliable etiological diagnosis and better genetic counseling of XLI.