Expanding the phenotypic spectrum of PORCN variants in two males with syndromic microphthalmia

The role of genes and environment in the etiology of congenital diaphragmatic hernias

Structural birth defects are a common cause of abnormalities in newborns. While there are cases of structural birth defects arising due to monogenic defects or environmental exposures, many birth defects are likely caused by a complex interaction between genes and the environment. A structural birth defect with complex etiology is congenital diaphragmatic hernias (CDH), a common and often lethal disruption in diaphragm development. Mutations in more than 150 genes have been implicated in CDH pathogenesis. Although there is generally less evidence for a role for environmental factors in the etiology of CDH, deficiencies in maternal vitamin A and its derivative embryonic retinoic acid are strongly associated with CDH. However, the incomplete penetrance of CDH-implicated genes and environmental factors such as vitamin A deficiency suggest that interactions between genes and environment may be necessary to cause CDH. In this review, we examine the genetic and environmental factors implicated in diaphragm and CDH development. In addition, we evaluate the potential for gene-environment interactions in CDH etiology, focusing on the potential interactions between the CDH-implicated gene, Gata4, and maternal vitamin A deficiency.

Underlying genetic etiologies of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is often detectable prenatally. Advances in genetic testing have made it possible to obtain a molecular diagnosis in many fetuses with CDH. Here, we review the aneuploidies, copy number variants (CNVs), and single genes that have been clearly associated with CDH. We suggest that array-based CNV analysis, with or without a chromosome analysis, is the optimal test for identifying chromosomal abnormalities and CNVs in fetuses with CDH. To identify causative sequence variants, whole exome sequencing (WES) is the most comprehensive strategy currently available. Whole genome sequencing (WGS) with CNV analysis has the potential to become the most efficient and effective means of identifying an underlying diagnosis but is not yet routinely available for prenatal diagnosis. We describe how to overcome and address the diagnostic and clinical uncertainty that may remain after genetic testing, and review how a molecular diagnosis may impact recurrence risk estimations, mortality rates, and the availability and outcomes of fetal therapy. We conclude that after the prenatal detection of CDH, patients should be counseled about the possible genetic causes of the CDH, and the genetic testing modalities available to them, in accordance with generally accepted guidelines for pretest counseling in the prenatal setting.

Novel insights into PORCN mutations, associated phenotypes and pathophysiological aspects

BACKGROUND

Goltz syndrome (GS) is a X-linked disorder defined by defects of mesodermal- and ectodermal-derived structures and caused by PORCN mutations. Features include striated skin-pigmentation, ocular and skeletal malformations and supernumerary or hypoplastic nipples. Generally, GS is associated with in utero lethality in males and most of the reported male patients show mosaicism (only three non-mosaic surviving males have been described so far). Also, precise descriptions of neurological deficits in GS are rare and less severe phenotypes might not only be caused by mosaicism but also by less pathogenic mutations suggesting the need of a molecular genetics and functional work-up of these rare variants.

RESULTS

We report two cases: one girl suffering from typical skin and skeletal abnormalities, developmental delay, microcephaly, thin corpus callosum, periventricular gliosis and drug-resistant epilepsy caused by a PORCN nonsense-mutation (c.283C > T, p.Arg95Ter). Presence of these combined neurological features indicates that CNS-vulnerability might be a guiding symptom in the diagnosis of GS patients. The other patient is a boy with a supernumerary nipple and skeletal anomalies but also, developmental delay, microcephaly, cerebral atrophy with delayed myelination and drug-resistant epilepsy as predominant features. Skin abnormalities were not observed. Genotyping revealed a novel PORCN missense-mutation (c.847G > C, p.Asp283His) absent in the Genome Aggregation Database (gnomAD) but also identified in his asymptomatic mother. Given that non-random X-chromosome inactivation was excluded in the mother, fibroblasts of the index had been analyzed for PORCN protein-abundance and -distribution, vulnerability against additional ER-stress burden as well as for protein secretion revealing changes.

CONCLUSIONS

Our combined findings may suggest incomplete penetrance for the p.Asp283His variant and provide novel insights into the molecular etiology of GS by adding impaired ER-function and altered protein secretion to the list of pathophysiological processes resulting in the clinical manifestation of GS.

Structural model of human PORCN illuminates disease-associated variants and drug-binding sites

Wnt signaling is essential for normal development and is a therapeutic target in cancer. The enzyme PORCN, or porcupine, is a membrane-bound O-acyltransferase (MBOAT) that is required for the post-translational modification of all Wnts, adding an essential mono-unsaturated palmitoleic acid to a serine on the tip of Wnt hairpin 2. Inherited mutations in PORCN cause focal dermal hypoplasia, and therapeutic inhibition of PORCN slows the growth of Wnt-dependent cancers. Based on homology to mammalian MBOAT proteins, we developed and validated a structural model of human PORCN. The model accommodates palmitoleoyl-CoA and Wnt hairpin 2 in two tunnels in the conserved catalytic core, shedding light on the catalytic mechanism. The model predicts how previously uncharacterized human variants of uncertain significance can alter PORCN function. Drugs including ETC-159, IWP-L6 and LGK-974 dock in the PORCN catalytic site, providing insights into PORCN pharmacologic inhibition. This structural model enhances our mechanistic understanding of PORCN substrate recognition and catalysis, as well as the inhibition of its enzymatic activity, and can facilitate the development of improved inhibitors and the understanding of disease-relevant PORCN mutants. This article has an associated First Person interview with the joint first authors of the paper.

Fragmented Elastic Fibers in Focal Dermal Hypoplasia (Goltz-Gorlin Syndrome) Without Focal Dermal Hypoplasia: Report of a Male Case and Review of the Literature

Goltz-Gorlin syndrome (GGS) (focal dermal hypoplasia) is a very rare developmental disorder affecting ectodermal and mesodermal structures. The syndrome is inherited in an X-linked manner, with the majority of affected individuals being female. We report the case of a 51-year-old man presenting with congenital skin lesions, syndactyly, facial and thoracic asymmetry, inguinal and laryngeal papillomas, cryptorchidism, polythelia, and dental anomalies. Molecular genetic analysis confirmed the clinically suspected diagnosis of GGS by detecting a known pathogenic mutation in the PORCN gene, c.502G>A [p.(Gly168Arg)] in the mosaic state. Histopathological examinations of skin biopsies of affected individuals typically show focal dermal hypoplasia and fat herniation; despite numerous skin biopsies, these characteristics were not found in the patient involved. Instead, we observed a notable reduction and fragmentation of the elastic fibers in the upper dermis. A systematic literature review regarding the histopathological presence or absence of dermal hypoplasia and/or information on elastic fibers revealed 240 histopathological descriptions of 173 individuals. Absence of dermal hypoplasia was found in 21 biopsies (8.8%). Information on elastic fibers was given in 47 cases (19.6%), showing decrease/absence in 31 cases and fragmentation of elastic fibers in 11 cases. Therefore, the histopathological absence of dermal hypoplasia does not exclude the diagnosis of the GGS. Decrease and fragmentation of elastic fibers may represent new histopathological clues to the diagnosis of this rare syndrome. At the same time, GGS should be included in the histopathological differential diagnoses of elastolytic disorders.

Goltz-Gorlin Syndrome: Revisiting the Clinical Spectrum

OBJECTIVE

To describe the varying phenotypic spectrum of Focal Dermal Hypoplasia (FDH) and to emphasize the need for identifying the condition in mildly affected females which is crucial for offering a prenatal diagnosis in subsequent pregnancy owing to the risk of having a severely affected baby.

METHODS

The phenotype-genotype correlation of 4 patients with FDH, over a period of 11 y from the genetic clinic in a tertiary care centre from Kerala, India was done.

RESULTS

All four mutation proven patients were females (2 adults and 2 children). One of the adult female subjects were mildly affected, though she had a history of having a severely affected female child who expired on day six. Among the 2 affected children, one of them had an unaffected mother and the other had an affected mother.

CONCLUSIONS

FDH has a wide clinical spectrum from very subtle findings to severe manifestations. The lethality of the condition in males and the disfigurement and multisystem involvement in females highlights the importance of confirmation of diagnosis by molecular analysis so that the family can be offered prenatal diagnosis in subsequent pregnancy.

Goltz syndrome in males: A clinical report of a male patient carrying a novel PORCN variant and a review of the literature

Here, we report a novel mosaic mutation in the PORCN gene in a male Goltz syndrome patient. We also compare the phenotypes of all reported males with a confirmed molecular diagnosis. This report serves to further clarify the phenotype of Goltz syndrome and suggests that expression in males varies.

Wnt lipidation: Roles in trafficking, modulation, and function

The Wnt signaling pathway consists of various downstream target proteins that have substantial roles in mammalian cell proliferation, differentiation, and development. Its aberrant activity can lead to uncontrolled proliferation and tumorigenesis. The posttranslational connection of fatty acyl chains to Wnt proteins provides the unique capacity for regulation of Wnt activity. In spite of the past belief that Wnt molecules are subject to dual acylation, it has been shown that these proteins have only one acylation site and undergo monounsaturated fatty acylation. The Wnt monounsaturated fatty acyl chain is more than just a hydrophobic coating and appears to be critical for Wnt signaling, transport, and receptor activation. Here, we provide an overview of recent findings in Wnt monounsaturated fatty acylation and the mechanism by which this lipid moiety regulates Wnt activity from the site of production to its receptor interactions.

A comprehensive clinical and genetic study in 127 patients with ID in Kinshasa, DR Congo

Pathogenic variants account for 4 to 41% of patients with intellectual disability (ID) or developmental delay (DD). In Sub-Saharan Africa, the prevalence of ID is thought to be higher, but data in Central Africa are limited to some case reports. In addition, clinical descriptions of some syndromes are not available for this population. This study aimed at providing an estimate for the fraction of ID/DD for which an underlying etiological genetic cause may be elucidated and provide insights into their clinical presentation in special institutions in a Central African country. A total of 127 patients (33 females and 94 males, mean age 10.03 ± 4.68 years), were recruited from six institutions across Kinshasa. A clinical diagnosis was achieved in 44 but molecular confirmation was achieved in 21 of the 22 patients with expected genetic defect (95% clinical sensitivity). Identified diseases included Down syndrome (15%), submicroscopic copy number variants (9%), aminoacylase deficiency (0.8%), Partington syndrome in one patient (0.8%) and his similarly affected brother, X-linked syndromic Mental Retardation type 33 (0.8%), and two conditions without clear underlying molecular genetic etiologies (Oculo-Auriculo-Vertebral and Amniotic Bands Sequence). We have shown that genetic etiologies, similar to those reported in Caucasian subjects, are a common etiologic cause of ID in African patients from Africa. We have confirmed the diagnostic utility of clinical characterization prior to genetic testing. Finally, our clinical descriptions provide insights into the presentation of these genetic diseases in African patients.

A Novel PORCN Frameshift Mutation Leading to Focal Dermal Hypoplasia: A Case Report

Focal dermal hypoplasia (FDH), also known as Goltz-Gorlin syndrome, is a rare, multisystemic, X-linked dominant genodermatosis characterized by defective development of mesodermal and ectodermal tissues. Major clinical features of the disorder are skin manifestations, skeletal defects, and developmental eye abnormalities. FDH is caused by heterozygous mutations in the PORCN gene located at Xp11.23, and 90% of individuals with FDH are females. Here, we report a female patient with cutaneous changes, multiple eye anomalies, short stature, and ectrodactyly of the right foot. These clinical findings were compatible with the diagnosis of FDH, and a novel mutation, NM_022825.3:c.488delG was found in the PORCN gene causing a premature stop codon.

Importance of complete phenotyping in prenatal whole exome sequencing

Whole exome sequencing (WES) is an emerging technique in prenatal diagnosis. In this retrospective study, we examined diagnostic utility and limitations of WES in prenatal cases with structural birth defects. DNA from 20 trios (fetal and parental), with normal karyotype and microarray findings, underwent WES and variant interpretation at a reference laboratory. The WES results were later re-evaluated in our academic center utilizing prenatal and postnatal phenotyping. Initial analysis using only prenatal ultrasound findings revealed no pathogenic or likely pathogenic variants in 20 pregnancies with structural birth defects. Re-analysis of WES variants and combination of prenatal and postnatal phenotyping yielded pathogenic variants in at least 20% of cases including PORCN gene in a fetus with split-hand/foot malformation, as well as variants of uncertain significance in NEB and NOTCH1 in fetuses with postnatal muscle weakness and Adams-Oliver syndrome, respectively. Furthermore, Sanger sequencing in a patient with holoprosencephaly, elucidated by postnatal MRI, revealed a pathogenic 47-base pairs deletion in ZIC2 which was missed by prenatal WES. This study suggests that incomplete prenatal phenotyping and lack of prenatal ultrasound-genotype databases are the limiting factors for current interpretation of WES data in prenatal diagnosis. Development of prenatal phenotype-genotype databases would significantly help WES interpretation in this setting. Patients who underwent prenatal clinical WES may benefit from the re-analysis based on detailed postnatal findings.

Congenital diaphragmatic hernia as a part of Nance-Horan syndrome?

Nance-Horan syndrome is a rare X-linked developmental disorder characterized by bilateral congenital cataract, dental anomalies, facial dysmorphism, and intellectual disability. Here, we identify a patient with Nance-Horan syndrome caused by a new nonsense NHS variant. In addition, the patient presented congenital diaphragmatic hernia. NHS gene expression in murine fetal diaphragm was demonstrated, suggesting a possible involvement of NHS in diaphragm development. Congenital diaphragmatic hernia could result from NHS loss of function in pleuroperitoneal fold or in somites-derived muscle progenitor cells leading to an impairment of their cells migration.

A non-mosaic PORCN mutation in a male with severe congenital anomalies overlapping focal dermal hypoplasia

Mutations in the PORCN gene cause the X-linked dominant condition focal dermal hypoplasia (FDH). Features of FDH include striated pigmentation of the skin, ocular and skeletal malformations. FDH is generally associated with in utero lethality in non-mosaic males and most of the currently reported male patients show mosaicism due to de novo post-zygotic mutations in the PORCN gene. There is only one previous report of a surviving male with an inherited mutation in the PORCN gene. Here, we report two male siblings with multiple malformations including skeletal, ocular and renal defects overlapping with FDH. A novel PORCN mutation (p.Ser250Phe) was identified in a non-mosaic, hemizygous state in one of the siblings who survived to 8 years of age. The mother is a heterozygous carrier, has a random X-inactivation pattern and is asymptomatic. Findings unusual for FDH include dysplastic clavicles and bilateral Tessier IV facial clefts. This is the second case report of a non-mosaic PORCN mutation in a male individual with multiple congenital anomalies. While the pathogenicity of this mutation remains to be further investigated, the survival of a male with a non-mosaic mutation in PORCN is suggestive of a functionally mild mutation leading to an X-linked recessive mode of inheritance.

Prenatal diagnosis of focal dermal hypoplasia: Report of three fetuses and review of the literature

Focal dermal hypoplasia (FDH) is a rare syndrome characterized by pleiotropic features knowing to involve mostly skin and limbs. Although FDH has been described in children and adults, the cardinal signs of the fetal phenotype are not straightforward impacting the quality of the prenatal diagnosis. We describe in depth the ultrasound, radiological, macroscopical, and histological phenotype of three female fetuses with a severe form of FDH, propose a review of the literature and an attempt to delineate minimal and cardinal signs for FDH diagnosis. This report confirms the variability of FDH phenotype, highlights unreported FDH features, and allows delineating evocative clinical associations for prenatal diagnosis, namely intrauterine growth retardation, limbs malformations, anterior wall/diaphragm defects, and eye anomalies. © 2016 Wiley Periodicals, Inc.

X inactivation and reactivation in X-linked diseases

X chromosome inactivation (XCI) is the phenomenon by which mammals compensate for dosage of X-linked genes in females (XX) versus males (XY). XCI patterns can be random or show extreme skewing, and can modify the mode of inheritance of X-driven phenotypes, which contributes to the variability of human pathologies. Recent findings have shown reversibility of the XCI process, which has opened new avenues in the approaches used for the treatment of X-linked diseases.

Novel mutations in PAX6, OTX2 and NDP in anophthalmia, microphthalmia and coloboma

Anophthalmia and microphthalmia (A/M) are developmental ocular malformations defined as the complete absence or reduction in size of the eye. A/M is a highly heterogeneous disorder with SOX2 and FOXE3 playing major roles in dominant and recessive pedigrees, respectively; however, the majority of cases lack a genetic etiology. We analyzed 28 probands affected with A/M spectrum (without mutations in SOX2/FOXE3) by whole-exome sequencing. Analysis of 83 known A/M factors identified pathogenic/likely pathogenic variants in PAX6, OTX2 and NDP in three patients. A novel heterozygous likely pathogenic variant in PAX6, c.767T>C, p.(Val256Ala), was identified in two brothers with bilateral microphthalmia, coloboma, primary aphakia, iris hypoplasia, sclerocornea and congenital glaucoma; the unaffected mother appears to be a mosaic carrier. While A/M has been reported as a rare feature, this is the first report of congenital primary aphakia in association with PAX6 and the identified allele represents the first variant in the PAX6 homeodomain to be associated with A/M. A novel pathogenic variant in OTX2, c.651delC, p.(Thr218Hisfs*76), in a patient with syndromic bilateral anophthalmia and a hemizygous pathogenic variant in NDP, c.293 C>T, p.(Pro98Leu), in two brothers with isolated bilateral microphthalmia and sclerocornea were also identified. Pathogenic/likely pathogenic variants were not discovered in the 25 remaining A/M cases. This study underscores the utility of whole-exome sequencing for identification of causative mutations in highly variable ocular phenotypes as well as the extreme genetic heterogeneity of A/M conditions.

Prenatal management of the fetus with isolated congenital diaphragmatic hernia in the era of the TOTAL trial

Congenital diaphragmatic hernia (CDH) may be isolated or associated with other structural anomalies, the latter with poor prognosis. The defect allows viscera to herniate through the defect into the chest, competing for space with the developing lungs. At birth, pulmonary hypoplasia leads to respiratory insufficiency and persistent pulmonary hypertension that is lethal in up to 30% of patients. When isolated, survival chances can be predicted by antenatal measurement of lung size and liver herniation. Chromosomal microarrays and exome sequencing contribute to understanding genetic factors underlying isolated CDH. Prenatal intervention aims at stimulating lung development, clinically achieved by percutaneous fetal endoscopic tracheal occlusion (FETO) under local anesthesia. The Tracheal Occlusion To Accelerate Lung growth trial (www.totaltrial.eu) is an international randomized trial investigating the role of fetal therapy for severe and moderate pulmonary hypoplasia. Despite an apparent increase in survival following FETO, the search for lesser invasive and more potent prenatal interventions must continue.