Digenic inheritance of an autosomal recessive hypotrichosis in two consanguineous pedigrees

Digenic genotypes: The interface of inbreeding, linkage, and linkage disequilibrium

Many traits in populations are well understood as being Mendelian effects at single loci or additive polygenic effects across numerous loci. However, there are important phenomena and traits that are intermediate between these two extremes and are known as oligogenic traits. Here we investigate digenic, or two-locus, traits and how their frequencies in populations are affected by non-random mating, specifically inbreeding, linkage disequilibrium, and selection. These effects are examined both separately and in combination to demonstrate how many digenic traits, especially double homozygous ones, can show significant, sometimes unexpected, changes in population frequency with inbreeding, linkage, and linkage disequilibrium. The effects of selection on deleterious digenic traits are also detailed. These results are applied to both digenic traits of medical significance as well as measuring inbreeding in natural populations.

A Novel Pathogenic CDH3 Variant underlying Heredity Hypotrichosis Simplex detected by Whole-Exome Sequencing (WES)-A Case Report

BACKGROUND

Heredity Hypotrichosis Simplex (HHS) is a rare non-syndromic disease form of Hypotrichosis Simplex (HS) characterized by progressive hair follicle (HF) miniaturization. It is usually inherited in an autosomal dominant manner. The differential diagnosis of HHS and the treatments remain challenging despite recent advancement. In this report, we describe a 19-year old female affected with HHS alongside most of her family members.

METHODS

Whole Exome Sequencing (WES) was performed for some of the family members to unravel the culprit gene involved in HHS phenotype and ascertain the dermatological examination that was done to classify the phenotypes of the disease.

RESULTS

A novel pathogenic variant in the CDH3 gene (p.Ser223GlyfsTer4) was identified as a plausible disease-causing variant for HHS.

CONCLUSION

This is the first report to associate CDH3 variants with a HHS phenotype without macular degeneration using WES. WES is an important tool for genotype-phenotype correlation, precision in diagnosis, and in-depth understanding of the disease mechanisms, leading to possible novel therapeutic targets treatment and better patient's outcomes.

New CDH3 mutation in the first Spanish case of hypotrichosis with juvenile macular dystrophy, a case report

Background

CDH3 on 16q22.1 is responsible for two rare autosomal recessive disorders with hypotrichosis and progressive macular dystrophy: Hypotrichosis with Juvenile Macular Dystrophy and Ectodermal Dysplasia, Ectrodactyly and Macular Dystrophy. We present a new case of Hypotrichosis with Juvenile Macular Dystrophy.

Case presentation

A Spanish male born in 1998 from non-consanguineous healthy parents with a suspected diagnosis of Keratosis Follicularis Spinulosa Decalvans and Retinitis Pigmentosa Inversa referred to our Genetics Department (IIS-Fundación Jiménez Díaz).

Molecular study of ABCA4 was performed, and a heterozygous missense p.Val2050Leu variant in ABCA4 was found.

Clinical revision reclassified this patient as Hypotrichosis with Juvenile Macular Dystrophy. Therefore, further CDH3 sequencing was performed showing a novel maternal missense change p.Val205Met (probably pathogenic by in silico analysis), and a previously reported paternal frameshift c.830del;p.Gly277Alafs*20, thus supporting the clinical diagnosis..

Conclusions

This is not only the first Spanish case with this clinical and molecular diagnosis, but a new mutation has been described in CDH3. Moreover, this work reflects the importance of joint assessment of clinical signs and evaluation of pedigree for a correct genetic study approach and diagnostic.

Epistatic interactions between at least three loci determine the "rat-tail" phenotype in cattle

BACKGROUND

The "rat-tail" syndrome (RTS) is an inherited hypotrichosis in cattle, which is exclusively expressed in diluted coloured hair. The affected animals also suffer from disturbed thermoregulation, which impairs their health and growth performance. Phenotypic features that are similar to RTS are observed in dogs with black hair follicle dysplasia.

RESULTS

We used a resource cross population between German Holstein and Charolais cattle breeds to prove that epistatic interactions between at least three independent genetic loci are required for the expression of the RTS phenotype. In this population, the RTS is exclusively expressed in animals with a eumelanic background that is due to the dominant E (D) allele at the melanocortin 1 receptor gene located on Bos taurus autosome (BTA) 18. In addition, only the individuals that are heterozygous at the dilution locus on BTA5 that corresponds to the premelanosome protein or silver gene variant c.64G>A were classified as displaying a RTS phenotype. Linkage and whole-genome association analyses using different models and different pedigrees allowed us to map a third locus (hereafter referred to as the RTS locus) that is essential for the expression of the RTS phenotype to the chromosomal region between 14 and 22 Mb on BTA5. Our findings clearly demonstrate that the RTS and dilution loci are distinct loci on BTA5.

CONCLUSIONS

Our study provides evidence that the RTS locus has effects on hair conformation and coat colour dilution and that the effect on coat colour dilution is clearly independent from that of the dilution locus. Finally, our results excluded several other loci that were previously reported to be associated with or to underlie hair conformation or pigmentation traits as the causal mutations of RTS and also several major functional candidate genes that are associated with hypotrichosis in humans. Our finding on the identification of a three-locus interaction that underlies RTS provides a prime example of epistatic interaction between several independent loci that is required for the expression of a distinct phenotype.

Phenotypic observations in "hypotrichosis with juvenile macular dystrophy" (recessive CDH3 mutations)

PURPOSE

Recessive mutations in CDH3 cause "hypotrichosis with juvenile macular dystrophy," typically recognized by the presence of prominent dermatological features. We report novel phenotypic observations and associated mutations in four patients from three families, including one who did not have frank hypotrichosis.

METHODS

Retrospective case series (2010-2014).

RESULTS

Four affected individuals from three consanguineous Arabian families were identified. All four subjects (two sisters and two unrelated males; 5, 13, 17, and 26 years old) had homozygous recessive CDH3 mutations not previously associated with the condition (c.307C>T; p.R103 in two sisters, c.1859_1862delCTCT in both unrelated males). Symptomatic visual loss was since birth or early childhood. One male subject did not have frank hypotrichosis, but review of symptoms revealed relatively slow hair growth and an inability to conceive children. None had dental or digital findings, although one female noted slow nail growth. All had a circumscribed central maculopathy with borders that did not respect posterior pole horizontal arterioles (typically extending beyond the major arcades) and associated with polygonal pigment clumping. Recognition of this pattern led us to suspect the diagnosis in the male without frank hypotrichosis. Retinal dysfunction was cone-rod (rather than macular only) by ERG in one patient, who developed severe central macular atrophy and a macular hole.

CONCLUSIONS

Ophthalmologists should consider the diagnosis of CDH3-related retinopathy in individuals with such clinical features whether or not there is frank hypotrichosis.

Digenic inheritance in medical genetics

Digenic inheritance (DI) is the simplest form of inheritance for genetically complex diseases. By contrast with the thousands of reports that mutations in single genes cause human diseases, there are only dozens of human disease phenotypes with evidence for DI in some pedigrees. The advent of high-throughput sequencing (HTS) has made it simpler to identify monogenic disease causes and could similarly simplify proving DI because one can simultaneously find mutations in two genes in the same sample. However, through 2012, I could find only one example of human DI in which HTS was used; in that example, HTS found only the second of the two genes. To explore the gap between expectation and reality, I tried to collect all examples of human DI with a narrow definition and characterise them according to the types of evidence collected, and whether there has been replication. Two strong trends are that knowledge of candidate genes and knowledge of protein–protein interactions (PPIs) have been helpful in most published examples of human DI. By contrast, the positional method of genetic linkage analysis, has been mostly unsuccessful in identifying genes underlying human DI. Based on the empirical data, I suggest that combining HTS with growing networks of established PPIs may expedite future discoveries of human DI and strengthen the evidence for them.

CDH3-Related Syndromes: Report on a New Mutation and Overview of the Genotype-Phenotype Correlations

Hypotrichosis with juvenile macular dystrophy (HJMD) and ectodermal dysplasia, ectrodactyly and macular dystrophy (EEM) are both caused by mutations in the CDH3 gene. In this report, we describe a family with EEM syndrome caused by a novel CDH3 gene mutation and review the mutation spectrum and limb abnormalities in both EEM and HJMD. A protein structure model showing the localization of different mutations causing both syndromes is presented. The CDH3 gene was sequenced and investigation of the mutations performed using a protein structure model. The conservation score was calculated by ConSurf. We identified a novel CDH3 gene mutation, p.G277V, which resides in a conserved residue located on a β-strand in the second cadherin domain. Review of the data on previously published mutations showed intra-familial and inter-familial variations in the severity of the limb abnormalities. Syndactyly was the most consistent clinical finding present in all the patients regardless of mutation type. The results of our study point to a phenotypic continuum between HJMD and EEM. It is important for genetic counseling to keep in mind the possible clinical/phenotypic overlap between these 2 syndromes and to be aware of the possible risk of limb abnormalities in future pregnancies in families with HJMD syndrome. CDH3 gene mutation screening is recommended in patients with both these syndromes as part of the work-up in order to offer appropriate genetic counseling.

Novel mutations in the keratin-74 (KRT74) gene underlie autosomal dominant woolly hair/hypotrichosis in Pakistani families

Autosomal dominant woolly hair (ADWH) is an inherited condition of tightly curled and twisted scalp hair. Recently, a mutation in human keratin-74 (KRT74) gene has been shown to cause this form of hereditary hair disorder. In the present study, we have described two families (A and B) having multiple individuals affected with autosomal dominant form of hair loss disorders. In family A, 10 individuals showed ADWH phenotype while in the family B, 14 individuals showed hypotrichosis of the scalp. Genotyping using polymorphic microsatellite markers showed linkage of both the families to type II keratin gene cluster on the chromosome 12q12-14.1. Mutation analysis of the KRT74 gene identified two novel mutations in the affected individuals of the families. The sequence analysis revealed a splice acceptor site mutation (c.IVS8-1G>A) in family A and a missense variant (c.1444G>A, p.Asp482Asn) in family B. Mutations identified in the present study extend the body of evidence implicating the KRT74 gene in the pathogenesis of autosomal dominant hair loss disorders.