Full-length Isoform Sequencing for Resolving the Molecular Basis of Charcot-Marie-Tooth 2A.

Objectives: Transcript sequencing of patient-derived samples has been shown to improve the diagnostic yield for solving cases of suspected Mendelian conditions, yet the added benefit of full-length long-read transcript sequencing is largely unexplored. Methods: We applied short-read and full-length transcript sequencing and mitochondrial functional studies to a patient-derived fibroblast cell line from an individual with neuropathy that previously lacked a molecular diagnosis. Results: We identified an intronic homozygous MFN2 c.600-31T>G variant that disrupts the branch point critical for intron 6 splicing. Full-length long-read isoform complementary DNA (cDNA) sequencing after treatment with a nonsense-mediated mRNA decay (NMD) inhibitor revealed that this variant creates 5 distinct altered splicing transcripts. All 5 altered splicing transcripts have disrupted open reading frames and are subject to NMD. Furthermore, a patient-derived fibroblast line demonstrated abnormal lipid droplet formation, consistent with MFN2 dysfunction. Although correctly spliced full-length MFN2 transcripts are still produced, this branch point variant results in deficient MFN2 levels and autosomal recessive Charcot-Marie-Tooth disease, axonal, type 2A (CMT2A). Discussion: This case highlights the utility of full-length isoform sequencing for characterizing the molecular mechanism of undiagnosed rare diseases and expands our understanding of the genetic basis for CMT2A.

Dominant-negative variant in SLC1A4 causes an autosomal dominant epilepsy syndrome.

SLC1A4 is a trimeric neutral amino acid transporter essential for shuttling L-serine from astrocytes into neurons. Individuals with biallelic variants in SLC1A4 are known to have spastic tetraplegia, thin corpus callosum, and progressive microcephaly (SPATCCM) syndrome, but individuals with heterozygous variants are not thought to have disease. We identify an 8-year-old patient with global developmental delay, spasticity, epilepsy, and microcephaly who has a de novo heterozygous three amino acid duplication in SLC1A4 (L86_M88dup). We demonstrate that L86_M88dup causes a dominant-negative N-glycosylation defect of SLC1A4, which in turn reduces the plasma membrane localization of SLC1A4 and the transport rate of SLC1A4 for L-serine.

Full-length isoform sequencing for resolving the molecular basis of Charcot-Marie-Tooth 2A.

Objectives: Transcript sequencing of patient derived samples has been shown to improve the diagnostic yield for solving cases of likely Mendelian disorders, yet the added benefit of full-length long-read transcript sequencing is largely unexplored. Methods: We applied short-read and full-length isoform cDNA sequencing and mitochondrial functional studies to a patient-derived fibroblast cell line from an individual with neuropathy that previously lacked a molecular diagnosis. Results: We identified an intronic homozygous MFN2 c.600-31T>G variant that disrupts a branch point critical for intron 6 spicing. Full-length long-read isoform cDNA sequencing after treatment with a nonsense-mediated mRNA decay (NMD) inhibitor revealed that this variant creates five distinct altered splicing transcripts. All five altered splicing transcripts have disrupted open reading frames and are subject to NMD. Furthermore, a patient-derived fibroblast line demonstrated abnormal lipid droplet formation, consistent with MFN2 dysfunction. Although correctly spliced full-length MFN2 transcripts are still produced, this branch point variant results in deficient MFN2 protein levels and autosomal recessive Charcot-Marie-Tooth disease, axonal, type 2A (CMT2A). Discussion: This case highlights the utility of full-length isoform sequencing for characterizing the molecular mechanism of undiagnosed rare diseases and expands our understanding of the genetic basis for CMT2A.

Molecular Pathway-Based Classification of Ectodermal Dysplasias: First Five-Yearly Update.

To keep pace with the rapid advancements in molecular genetics and rare diseases research, we have updated the list of ectodermal dysplasias based on the latest classification approach that was adopted in 2017 by an international panel of experts. For this purpose, we searched the databases PubMed and OMIM for the term "ectodermal dysplasia", referring mainly to changes in the last 5 years. We also tried to obtain information about those diseases on which the last scientific report appeared more than 15 years ago by contacting the authors of the most recent publication. A group of experts, composed of researchers who attended the 8th International Conference on Ectodermal Dysplasias and additional members of the previous classification panel, reviewed the proposed amendments and agreed on a final table listing all 49 currently known ectodermal dysplasias for which the molecular genetic basis has been clarified, including 15 new entities. A newly reported ectodermal dysplasia, linked to the gene LRP6, is described here in more detail. These ectodermal dysplasias, in the strict sense, should be distinguished from syndromes with features of ectodermal dysplasia that are related to genes extraneous to the currently known pathways involved in ectodermal development. The latter group consists of 34 syndromes which had been placed on the previous list of ectodermal dysplasias, but most if not all of them could actually be classified elsewhere. This update should streamline the classification of ectodermal dysplasias, provide guidance to the correct diagnosis of rare disease entities, and facilitate the identification of individuals who could benefit from novel treatment options.

Cardiovascular outcomes of pregnancy in Turner syndrome.

OBJECTIVES: Women with Turner syndrome (TS) are frequently counselled against pregnancy due to lack of data and unclear aortic dissection risk. However, with advances in fertility therapy, more women with TS are contemplating pregnancy. This study compared rates of adverse cardiovascular (CV) outcomes among: (1) pregnant and non-pregnant women with TS and (2) pregnant women with TS with/without structural heart disease. METHODS: Retrospective analysis of pregnant and age-matched non-pregnant controls with TS (2005-2017) across 10 CV centres was done. Data were collected at initial evaluation in pregnancy and outcomes were assessed to 6 months postpartum. Adverse CV events were defined as CV death, aortic dissection/rupture and/or aortic intervention. Non-pregnant age-matched controls were followed over the same time period. RESULTS: Sixty-eight pregnancies were included (60 women, mean age 33 years, 48% primigravid, 49% fertility therapy, 80% structurally normal heart, 25% XO karyotype). Based on American Society of Reproductive Medicine criteria, 10 pregnancies occurred in women stratified to high-risk category. There were no CV events in the pregnant women or in the non-pregnant women with TS. Obstetric events complicated 12 (18%) pregnancies with 9 (13%) attributed to hypertensive disorder of pregnancy. Fetal events included small for gestational age neonates (18%), preterm delivery (15%) and fetal death (3%). CONCLUSIONS: This study helps to refine the approach to pregnancy in women with TS. Among women with TS without structural heart disease, pregnancy does not impose an increased risk of CV outcomes. Among women with TS with structural heart disease, the risk of pregnancy is not as prohibitive as previously described but does require ongoing evaluation.

Ectodermal dysplasias: Classification and organization by phenotype, genotype and molecular pathway.

An international advisory group met at the National Institutes of Health in Bethesda, Maryland in 2017, to discuss a new classification system for the ectodermal dysplasias (EDs) that would integrate both clinical and molecular information. We propose the following, a working definition of the EDs building on previous classification systems and incorporating current approaches to diagnosis: EDs are genetic conditions affecting the development and/or homeostasis of two or more ectodermal derivatives, including hair, teeth, nails, and certain glands. Genetic variations in genes known to be associated with EDs that affect only one derivative of the ectoderm (attenuated phenotype) will be grouped as non-syndromic traits of the causative gene (e.g., non-syndromic hypodontia or missing teeth associated with pathogenic variants of EDA "ectodysplasin"). Information for categorization and cataloging includes the phenotypic features, Online Mendelian Inheritance in Man number, mode of inheritance, genetic alteration, major developmental pathways involved (e.g., EDA, WNT "wingless-type," TP63 "tumor protein p63") or the components of complex molecular structures (e.g., connexins, keratins, cadherins).

Postnatal outcomes of prenatally diagnosed 45,X/46,XX.

High quality information is critical for informed decision-making in pregnancy following a prenatal diagnosis of sex chromosome aneuploidy. The goal of this study was to define the spectrum of outcomes in patients with prenatally diagnosed 45,X/46,XX mosaic Turner syndrome in order to provide a better basis for genetic counseling at the time of intrauterine diagnosis. Phenotype data for twenty-five patients with prenatally diagnosed 45,X/46,XX mosaicism were collected by retrospective chart review and, when possible, semi-structured telephone interview. Existing data from a cohort of 58 patients with postnatally diagnosed 45,X/46,XX mosaicism were used for comparison. Relative to those diagnosed postnatally, prenatal patients were more likely to have normal growth and normal secondary sexual development, less likely to manifest distinctive Turner syndrome features such as nuchal webbing and edema, and had significantly fewer renal defects. These differences underscore the need for a nuanced approach to prenatal counseling in cases of 45,X/46,XX mosaicism.

A Point Mutation in PDGFRB Causes Autosomal-Dominant Penttinen Syndrome.

Penttinen syndrome is a distinctive disorder characterized by a prematurely aged appearance with lipoatrophy, epidermal and dermal atrophy along with hypertrophic lesions that resemble scars, thin hair, proptosis, underdeveloped cheekbones, and marked acro-osteolysis. All individuals have been simplex cases. Exome sequencing of an affected individual identified a de novo c.1994T>C p.Val665Ala variant in PDGFRB, which encodes the platelet-derived growth factor receptor ß. Three additional unrelated individuals with this condition were shown to have the identical variant in PDGFRB. Distinct mutations in PDGFRB have been shown to cause infantile myofibromatosis, idiopathic basal ganglia calcification, and an overgrowth disorder with dysmorphic facies and psychosis, none of which overlaps with the clinical findings in Penttinen syndrome. We evaluated the functional consequence of this causative variant on the PDGFRB signaling pathway by transfecting mutant and wild-type cDNA into HeLa cells, and transfection showed ligand-independent constitutive signaling through STAT3 and PLCγ. Penttinen syndrome is a clinically distinct genetic condition caused by a PDGFRB gain-of-function mutation that is associated with a specific and unusual perturbation of receptor function.

Ventral midline blanching in the setting of segmental infantile hemangiomas: clinical observations and pathogenetic implications.

Areas of blanched skin in children may be seen as an independent finding or in association with vascular birthmarks. We performed a retrospective chart review to identify and describe infants with areas of ventral midline blanching in the presence of segmental infantile hemangiomas. We identified nine full-term infants with partial or full segmental hemangiomas and areas of midline ventral blanching. Additional ventral wall defects were seen in five patients. Six had cardiac anomalies and six had intracranial anomalies. Five were diagnosed with definite PHACE (posterior fossa, hemangioma, arterial, cardiac, and eye abnormalities) syndrome and three had possible PHACE syndrome. Eight were complicated by ulceration. Treatment varied according to the case. Ventral blanching, even in the absence of overt midline defects, can be seen in infants with segmental hemangiomas at risk for PHACE syndrome. We hypothesize that midline blanching may represent a minor manifestation of a developmental ventral defect.

Folliculocystic and collagen hamartoma of tuberous sclerosis complex.

BACKGROUND: Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by tumors and hamartomas in several organs including the skin. OBJECTIVE: We sought to describe a new type of complex hamartoma in patients with TSC. METHODS: This was a retrospective clinical and histopathologic evaluation of 6 cases. RESULTS: The skin lesions consisted of large, painless, infiltrated plaques that were first noticed at birth or during early infancy on the abdomen, thigh, back, or scalp. In time, the plaques became studded with numerous follicular comedo-like openings and cysts containing and draining a keratinous or purulent material. The main histopathologic features were: abundant collagen deposition in the dermis and extending into the underlying fat; concentric, perifollicular fibrosis surrounding hair follicles; and comedones and keratin-containing cysts lined by infundibular epithelium, some of which were ruptured with secondary granulomatous reaction. Five of the 6 patients had a clinical diagnosis of TSC. LIMITATIONS: Genetic testing was performed in only one patient. CONCLUSION: This distinctive folliculocystic and collagen hamartoma has not been recognized previously in association with TSC.

Keratosis Follicularis Spinulosa Decalvans is caused by mutations in MBTPS2.

Keratosis Follicularis Spinulosa Decalvans (KFSD) is a rare genetic disorder characterized by development of hyperkeratotic follicular papules on the scalp followed by progressive alopecia of the scalp, eyelashes, and eyebrows. Associated eye findings include photophobia in childhood and corneal dystrophy. Due to the genetic and clinical heterogeneity of similar disorders, a definitive diagnosis of KFSD is often challenging. Toward identification of the causative gene we reanalyzed a large Dutch KFSD family. SNP arrays (1 M) redefined the locus to a 2.9-Mb region at Xp22.12-Xp22.11. Screening of all 14 genes in the candidate region identified MBTPS2 as the candidate gene carrying a c.1523A>G (p.Asn508Ser) missense mutation. The variant was also identified in two unrelated X-linked KFSD families and cosegregated with KFSD in all families. In symptomatic female carriers, skewed X-inactivation of the normal allele matched with increased severity of symptoms. MBTPS2 is required for cleavage of sterol regulatory element-binding proteins (SREBPs). In vitro functional expression studies of the c.1523A>G mutation showed that sterol responsiveness was reduced by half. Other missense mutations in MBTPS2 have recently been identified in patients with IFAP syndrome. We postulate that both phenotypes are in the spectrum of one genetic disorder with a partially overlapping phenotype.

Genetic counseling in epidermolysis bullosa.

This article contains the author's views on genetic counseling in cases concerning the epidermolysis bullosa syndromes. The provision of genetic counseling entails absolutes such as diagnosis, natural history, treatment, mode of inheritance, recurrence risks/prenatal diagnosis and referral. The genetic counselor needs to be informed and informative and answer all the needs of the patients and their families reliably both at the initial consultation and subsequently as needed over the course of the patient's life.

Dermatologic findings of ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome.

Hay-Wells syndrome, caused by mutations in the p63 gene, is an autosomal dominant ectodermal dysplasia with the main features of ankyloblepharon filiforme adnatum, ectodermal defects, and cleft lip/palate, from which the disorder's other name, AEC syndrome, is derived. The National Foundation for Ectodermal Dysplasias convened the International Research Symposium for AEC Syndrome on November 8-10, 2006, at Texas Children's Hospital/Baylor College of Medicine, Houston, TX with appropriate IRB approval. This multidisciplinary conference was the largest gathering of such patients to date and allowed us to further characterize dermatologic features of AEC syndrome, which included: sparse and wiry hair, nail changes, past or present scalp erosions, decreased sweat production, palmar/plantar changes, and unique pigmentary anomalies. Early recognition of the features of AEC syndrome and subsequent early diagnosis is important in minimizing invasive diagnostic studies, improving morbidity and mortality, and providing genetic counseling. Skin erosions, especially those of the scalp, were identified as the most challenging cutaneous aspect of this syndrome. Although the reasons for the skin erosions and poor healing are not known, mutations of p63 may lead to a diminished store of basal cells capable of replenishing the disrupted barrier. Therapeutic strategies currently under exploration include gene therapy, as well as epidermal stem cell therapy. Until then, gentle wound care and limiting further trauma seem to be the most prudent treatment modalities.

International Research Symposium on Ankyloblepharon-Ectodermal Defects-Cleft Lip/Palate (AEC) syndrome.

Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome (Hay-Wells syndrome, MIM #106220) is a rare autosomal dominant ectodermal dysplasia syndrome. It is due to mutations in the TP63 gene, known to be a regulatory gene with many downstream gene targets. TP63 is important in the differentiation and proliferation of the epidermis, as well as many other processes including limb and facial development. It is also known that mutations in TP63 lead to skin erosions. These erosions, especially on the scalp, are defining features of AEC syndrome and cause significant morbidity and mortality in these patients. It was this fact that led to the 2003 AEC Skin Erosion Workshop. That conference laid the groundwork for the International Research Symposium for AEC Syndrome held at Texas Children's Hospital in 2006. The conference brought together the largest cohort of individuals with AEC syndrome, along with a multitude of physicians and scientists. The overarching goals were to define the clinical and pathologic findings for improved diagnostic criteria, to obtain tissue samples for further study and to define future research directions. The symposium was successful in accomplishing these aims as detailed in this conference report. Following our report, we also present 11 manuscripts within this special section that outline the collective clinical, pathologic, and mutational data from 18 individuals enrolled in the concurrent Baylor College of Medicine IRB-approved protocol: Characterization of AEC syndrome. These collaborative findings will hopefully provide a stepping-stone to future translational projects of TP63 and TP63-related syndromes.

Hereditary woolly hair and keratosis pilaris.

We describe a family with woolly hair and ulerythema ophryogenes spanning four generations. Both woolly hair and ulerythema ophryogenes have been associated with Noonan syndrome and cardiofaciocutaneous syndrome (CFC), two disorders with considerable phenotypic overlap. This family did not exhibit any of the other findings characteristic of either Noonan syndrome or CFC, similar to a previously described pedigree with hereditary woolly hair. Woolly hair elicits a broad differential diagnosis, including woolly hair nevus and several genodermatoses. Our report reviews the evaluation of woolly hair and discusses the conditions associated with this physical finding.

Growth characteristics of children with ectodermal dysplasia syndromes.

OBJECTIVE: Clinical observations suggested that growth abnormalities may be present in children with ectodermal dysplasia (ED) syndromes. This study characterizes the longitudinal pattern of growth in a cohort of children with the ED syndromes. We hypothesized that (1) linear and ponderal growth abnormalities are present in children with ED from infancy through adolescence, and (2) linear and ponderal growth abnormalities differ among the clinical variants of these disorders. METHODS: We studied 138 children who had ED and were registered with the National Foundation for Ectodermal Dysplasias, 74% of whom had clinical features consistent with the hypohidrotic EDs (HEDs). Height (or length) and weight measurements were obtained by standardized techniques and from review of available medical records. We converted these measurements to weight-for-height (children younger than 5 years and <103 cm in length) or BMI (children > or =2 years old). Height, weight, weight-for-height, and BMI were converted to age- and gender-specific z scores. We applied linear regression, 1-sample t tests, and analysis of variance to detect linear and ponderal growth abnormalities in children with ED compared with a reference population. RESULTS: Mean weight-for-age, weight-for-height, and BMI-for-age z scores but not height-for-age z score, were significantly lower in children with the ED syndromes than in the reference population. Mean weight-for-age and weight-for-height z scores but not BMI-for-age or height-for-age z scores increased significantly with increasing age. The mean height-for-age z score of children with the ED syndromes other than the HEDs was significantly lower than that of children with the HEDs. CONCLUSIONS: Growth abnormalities, measured as weight deficits, were present at an early age in children with the ED syndromes and persisted through adolescence. Height deficits were seen only in children with ED syndromes other than HEDs. Clinicians should evaluate carefully children with ED syndromes for growth abnormalities.

Mosaicism in cutaneous pigmentation.

PURPOSE OF REVIEW: This article reviews the disorders of patterned dyspigmentation and discusses the pathogenesis of the pigmentary changes. RECENT FINDINGS: A range of cytogenetic abnormalities has been detected in patterned pigmentary disease. This molecular heterogeneity correlates with the wide spectrum of clinical phenotypes observed. Many of the molecular defects overlap with genes known to play a role in pigmentation. Our understanding of the underlying genetic mechanisms for these mosaic conditions is evolving with advances in technology and dissection of the molecular pathways involved in melanocyte biology. SUMMARY: The causal heterogeneity of patterned dyspigmentation promises to reveal clues about the differentiation, function, and control of melanocytes in embryonic and postnatal development.