Exploring the overlap between alopecia areata and major depressive disorder: Epidemiological and genetic perspectives

BACKGROUND

Research suggests that Alopecia areata (AA) and Major Depressive Disorder (MDD) show substantial comorbidity. To date, no study has investigated the hypothesis that this is attributable to shared genetic aetiology.

OBJECTIVES

To investigate AA-MDD comorbidity on the epidemiological and molecular genetic levels.

METHODS

First, epidemiological analyses were performed using data from a cohort of adult German health insurance beneficiaries (n = 1.855 million) to determine the population-based prevalence of AA-MDD comorbidity. Second, analyses were performed to determine the prevalence of MDD in a clinical AA case-control sample with data on psychiatric phenotypes, stratifying for demographic factors to identify possible contributing factors to AA-MDD comorbidity. Third, the genetic overlap between AA and MDD was investigated using a polygenic risk score (PRS) approach and linkage disequilibrium score (LDSC) regression. For PRS, summary statistics from a large MDD GWAS meta-analysis (PGC-MD2) were used as the training sample, while a Central European AA cohort, including the above-mentioned AA patients, and an independent replication US-AA cohort were used as target samples. LDSC was performed using summary statistics of PGC-MD2 and the largest AA meta-analysis to date.

RESULTS

High levels of AA-MDD comorbidity were reported in the population-based (MDD in 24% of AA patients), and clinical samples (MDD in 44% of AA patients). MDD-PRS explained a modest proportion of variance in AA case-control status (R²  = 1%). This signal was limited to the major histocompatibility complex (MHC) region on chromosome 6. LDSC regression (excluding MHC) revealed no significant genetic correlation between AA and MDD.

CONCLUSIONS

As in previous research, AA patients showed an increased prevalence of MDD. The present analyses suggest that genetic overlap may be confined to the MHC region, which is implicated in immune function. More detailed investigation is required to refine understanding of how the MHC is involved in the development of AA and MDD comorbidity.

Evolutionary distinct roles of γ-secretase subunit nicastrin in zebrafish and humans

BACKGROUND

Mutations in the genes that encode the human γ-secretase subunits Presenilin-1, Presenilin Enhancer Protein 2, and Nicastrin (NCSTN) are associated with familial hidradenitis suppurativa (HS); and, regarding Presenilin Enhancer Protein 2, also with comorbidity for the hereditary pigmentation disorder Dowling-Degos disease.

OBJECTIVE

Here, the consequences of targeted inactivation of ncstn, the zebrafish homologue of human NCSTN, were studied.

METHODS

After morpholino (MO)-mediated ncstn-knockdown, the possibilities of phenotype rescue through co-injection of ncstn-MO with wildtype zebrafish ncstn or human NCSTN mRNA were investigated. Further, the effects of the co-injection of a human missense, nonsense, splice-site, and frameshift mutation were studied.

RESULTS

MO-mediated ncstn-knockdown resulted in a significant reduction in melanophore morphology, size and number; and alterations in their patterns of migration and distribution. This phenotype was rescued by co-injection of zebrafish ncstn RNA, human NCSTN RNA, or a construct encoding the human NCSTN missense mutation p.P211R.

CONCLUSION

Human NCSTN mutations encoding null alleles confer loss-of-function regarding pigmentation homeostasis in zebrafisch. In contrast, the human missense mutation p.P211R was less harmful, asserting sufficient residual ncstn activity to maintain pigmentation in zebrafish. Since fish lack the anatomical structures affected by HS, our data suggest that the zebrafish ncstn gene and the human NCSTN gene have probably acquired different functions during evolution. In fish, one major role of ncstn is the maintenance of pigmentation homeostasis. In contrast, one of the roles of NCSTN in humans is the prevention of inflammatory processes in the adnexal structures of the skin, as seen in familial HS.

Isolated recessive nail dysplasia caused by FZD6 mutations: report of three families and review of the literature

Congenital abnormalities of the nail are rare conditions that are most frequently associated with congenital ectodermal syndromes involving several of the epidermal appendages including the skin, teeth, hair and nails. Isolated recessive nail dysplasia (IRND) is much rarer but has recently been recognized as a condition resulting in 20‐nail dystrophy in the absence of other cutaneous or extracutaneous findings. A few case reports have identified mutations in the Frizzled 6 (FZD6) gene in families presenting with abnormal nails consistent with IRND. These reports have highlighted the role of Wnt–FZD signalling in the process of nail formation. We report three families presenting with features of IRND, in whom we identified mutations in FZD6, including one previously unreported mutation.

A novel KRT86 mutation in a Turkish family with monilethrix, and identification of maternal mosaicism

BACKGROUND

Monilethrix is a rare monogenic dystrophic hair loss disorder with high levels of intrafamilial and interfamilial variability. It is characterized by diffuse occipital or temporal alopecia, hair fragility and follicular hyperkeratosis of the occipital region. Mutations in the keratin genes KRT81, KRT83 and KRT86 lead to autosomal dominant monilethrix, whereas mutations in the desmoglein 4 gene (DSG4) cause an autosomal recessive form.

AIM

To identify the mutation in a consanguineous Turkish family with three affected children and apparently unaffected parents.

METHODS

Sequencing analysis of the genes DSG4 and KRT86 was performed. SNaPshot analysis was conducted to quantify the proportion of cells carrying the KRT86 mutation and to confirm maternal mosaicism of KRT86.

RESULTS

No pathogenic mutation was found by sequencing analysis of DSG4; however, analysis of KRT86 revealed a novel mutation, c.1231G>T;p.Glu411*, in exon 7 in the three affected children and their mother. The mutation signal was weaker in the mother than in the three siblings, and SNaPshot analysis revealed substantial mutation-level variation between the children and their mother.

CONCLUSIONS

Our results extend the spectrum of KRT86 mutations and indicate KRT86 mosaicism in the family examined. This study is the first, to our knowledge, to describe mosaicism for a monogenic hair loss disorder, and suggests that mosaicism leads to a mild manifestation of monilethrix.

Investigation of the male pattern baldness major genetic susceptibility loci AR/EDA2R and 20p11 in female pattern hair loss

BACKGROUND

The aetiology of female pattern hair loss (FPHL) is largely unknown. However, it is hypothesized that FPHL and male pattern baldness (AGA) share common susceptibility alleles. The two major susceptibility loci for AGA are the androgen receptor (AR)/ectodysplasin A2 receptor (EDA2R) locus on the X-chromosome, and a locus on chromosome 20p11, for which no candidate gene has yet been identified.

OBJECTIVES

To examine the role of the AR/EDA2R and 20p11 loci in the development of FPHL using 145 U.K. and 85 German patients with FPHL, 179 U.K. supercontrols and 150 German blood donors.

METHODS

Patients and controls were genotyped for 25 single nucleotide polymorphisms (SNPs) at the AR/EDA2R locus and five SNPs at the 20p11 locus.

RESULTS

Analysis of the AR/EDA2R locus revealed no significant association in the German sample. However, a nominally significant association for a single SNP (rs1397631) was found in the U.K. sample. Subgroup analysis of the U.K. patients revealed significant association for seven markers in patients with an early onset (P = 0·047 after adjustment for the testing of multiple SNPs by Monte Carlo simulation). No significant association was obtained for the five 20p11 variants, either in the overall samples or in the analysis of subgroups.

CONCLUSIONS

The observed association suggests that the AR/EDA2R locus confers susceptibility to early-onset FHPL. Our results do not implicate the 20p11 locus in the aetiology of FPHL.

A premature termination mutation in a patient with Lowe syndrome without congenital cataracts: dropping the "O" in OCRL

The oculocerebrorenal syndrome of Lowe is an X-linked recessive disorder characterized by the triad of congenital cataracts, mental retardation and a renal proximal tubulopathy. Although severity of phenotype might vary, congenital cataracts are part of the definition of this rare disorder.We report a 13-year-old patient with the typical cerebrorenal phenotype of Lowe syndrome, that had remained undiagnosed due to absence of any ocular involvement. OCRL gene analysis was carried.DNA analysis revealed a c.C760T (p.Gln199X) nonsense mutation in exon 8 expected to cause complete disruption of OCRL function. After sequencing the parents of the index patient and his maternal grandparents, this mutation turned out to be de novo in the mother. Furthermore, a silent variant (p.Arg35=) was identified in exon 2, that could also be identified in the mother and her 3 sisters, but not in the grandparents assuming germ cell mosaicism in either of the grandparents. RNA analysis from the patient's lymphocytes revealed presence of full-length OCRL transcripts. Western blotting from lymphocyte samples failed to detect OCRL protein even in controls.Our findings extend the phenotypic spectrum caused by OCRL mutations and illustrate that there may be selective organ involvement in Lowe syndrome.

FZD6 encoding the Wnt receptor frizzled 6 is mutated in autosomal-recessive nail dysplasia

BACKGROUND

Isolated nail dysplasia is rare and has been reported in only a small number of families.

OBJECTIVES

To describe and characterize two Pakistani families with an autosomal-recessive inherited nail dysplasia.

METHODS

Genome-wide linkage analysis; mutation screening of candidate genes by Sanger sequencing; cloning of FZD6 and protein analyses; immunohistochemistry.

RESULTS

We mapped this genodermatosis to chromosome 8q22.3, and identified a homozygous nonsense mutation c.1750G>T (p.E584X) in the frizzled 6 (FZD6) gene in all affected individuals. Immunohistochemical analyses in nail sections from healthy individuals revealed strong expression of FZD6 in the ventral nail matrix and a less pronounced expression of FZD6 in the nail bed.

CONCLUSIONS

FZD6 belongs to a family of proteins that serve as receptors in Wnt signalling pathways, and has been shown to act as a negative regulator of the canonical Wnt/β-catenin signalling cascade and a positive regulator of the noncanonical Wnt or planar cell polarity pathway. The present results therefore suggest that FZD6 plays a pivotal role in the growth and guidance of the nail plate in humans by acting as a molecular switch between different Wnt pathways. Previous studies have identified mutations in the RSPO4 and LMX1B components of the Wnt pathway in patients with the hypoplastic nail disorders anonychia and nail-patella syndrome, respectively. Only recently, FZD6 mutations were identified in isolated nail dysplasia. The present results emphasize the important role of the Wnt pathways in nail development and increase understanding of Wnt-mediated developmental events in general.

Functional analysis of splice site mutations in the human hairless (HR) gene using a minigene assay

BACKGROUND

Congenital atrichia is a rare autosomal recessive form of isolated alopecia which is caused by mutations in the human hairless (HR) gene. Patients are born with normal hair that is shed almost completely and irreversibly during the first weeks of life.

OBJECTIVES

To investigate the molecular genetic basis of congenital atrichia in two patients, and to analyse the functional consequences of one newly identified and all seven previously identified HR splice site mutations using a minigene assay.

METHODS

Molecular analysis of the HR gene was performed by direct DNA sequencing. To analyse the functional consequences of the splice site mutations, the respective sequences were cloned into a vector which allows directed splicing. After transfection of COS7 cells, isolation of RNA and cDNA synthesis, sequencing was performed to analyse the products.

RESULTS

Two novel mutations were identified: an insertion in exon 2 (c.485insT; p.C162LfsX17), and a splice site mutation (c.2847-1G>A). In vitro analysis revealed aberrant splicing for all eight of the investigated HR splice site mutations. Comparison with the results of two biocomputational programs (neural network splice server and CRYP-SKIP) and calculation of consensus values revealed that the predictions of these two programs were consistent in only five and two of the eight mutations, respectively.

CONCLUSIONS

This is the first report to analyse the consequences of HR splice site mutations using a cell-based in vitro assay. The results highlight the importance of performing splicing experiments to clarify the consequences of putative splice site mutations.

Identification of a U2HR gene mutation in Turkish families with Marie Unna hereditary hypotrichosis

Marie Unna hereditary hypotrichosis (MUHH) is an autosomal dominant form of isolated alopecia. The disorder is characterized by the absence or scarcity of scalp hair, eyebrows and eyelashes at birth. Coarse wiry hair begins to grow during childhood, but this is followed by progressive hair loss, which usually begins around puberty. A recent study identified mutations in U2HR, an inhibitory upstream open reading frame in the 5'-untranslated region of the human hairless gene. We investigated three reportedly unrelated Turkish multigeneration families with MUHH. Using direct sequencing of U2HR we were able to identify the c. 2T>A (p.M1K) mutation in one index patient of each family. The mutation cosegregates perfectly with the disease in all members of the families. To our knowledge, this is the first time that a mutation in U2HR has been identified in families from the Middle East. The observation of a common mutation is suggestive of a possible founder effect.

The TRAF1/C5 locus confers risk for familial and severe alopecia areata

BACKGROUND

Alopecia areata (AA) is a common hair loss disorder with a complex mode of inheritance. Autoimmune mechanisms are presumed to be crucial aetiologically. It is plausible that a number of autoimmune disorders may share a common genetic background. This phenomenon has been demonstrated in previous studies, which have shown an overlap of susceptibility alleles between AA and other autoimmune disorders. Recent studies have shown that genetic variants on the TRAF1/C5 (tumor necrosis factor receptor-associated factor 1, complement component 5) locus confer susceptibility to rheumatoid arthritis (RA).

OBJECTIVES

To examine the role of the TRAF1/C5 locus in the development of AA using a large sample of 1,195 patients with AA and 1280 controls.

METHODS

We genotyped the two most significant single nucleotide polymorphisms (SNPs) (rs10818488, rs2416808) from a former RA candidate gene study. After having obtained evidence for association, we performed a fine-mapping study and genotyped the locus with an additional 27 SNPs.

RESULTS

While no significant result was obtained for the overall sample, rs2416808 showed significant associations in the analysis of the subgroups with severe AA and with a positive family history. The most significant P-value for rs2416808 was in familial cases (P = 0.004, P(corr) = 0.026). The fine mapping revealed significant associations for four additional SNPs in the analysis of subgroups, with rs2416808 remaining the most significant marker.

CONCLUSIONS

Our results point to the involvement of the TRAF1/C5 locus in the aetiology of familial and severe AA, and provide further support for a shared aetiology between AA and other autoimmune disorders.

Richner-Hanhart syndrome detected by expanded newborn screening

Richner-Hanhart syndrome (tyrosinemia type 2) is an inborn error of tyrosine metabolism which is clinically characterized mainly by oculocutaneous symptoms including corneal opacities and keratosis palmoplantaris. Skin symptoms usually develop after the first year of life. We report a neonate in whom already on the third day of life diagnosis of Richner-Hanhart syndrome could be suspected because of elevated tyrosine levels in newborn screening by tandem mass spectrometry. Analysis of the tyrosine aminotransferase gene revealed a homozygous missense mutation p.R433W (c.1297C>T). An 8-year-old brother with persistent plantar hyperkeratotic plaques of the soles of yet unknown origin was subsequently identified to be also affected with Richner-Hanhart syndrome. This demonstrates that early diagnosis of Richner-Hanhart syndrome is possible in neonates by extended newborn screening. Early introduction of dietary treatment is a prerequisite to reduce the risk of clinical symptoms.

The R620W polymorphism in PTPN22 confers general susceptibility for the development of alopecia areata

BACKGROUND

The functional R620W (c.1858C>T) variant of the protein tyrosine phosphatase nonreceptor 22 gene (PTPN22) has been associated with a variety of autoimmune disorders. A recent study has suggested that R620W also contributes to the severe form of alopecia areata (AA).

OBJECTIVES

We sought to replicate the finding of an association between PTPN22 and severe AA. In addition, we wanted to study the effect of PTPN22 on the general risk to develop AA and on other subtypes of AA (mild AA, early/late age at onset, positive/negative family history).

METHODS

The R620W variant was genotyped in a large case-control sample of Belgian-German origin with 435 patients and 628 controls.

RESULTS

Significant results were obtained for the overall collective of patients with AA (P=0.007). Subdividing the sample according to severity of AA, family history and age at onset, we detected lowest P-values for patients with the severe form of AA (Pcorr=0.036), with a positive family history (Pcorr=0.042) and with an age at onset<or=20 years (Pcorr=0.048).

CONCLUSIONS

Our results suggest the R620W variant of PTPN22 as a general risk factor in AA with the strongest effect observed among patients with a severe type of AA, a positive family history or an early onset of disease.

Investigation of the functional variant c.-169T > C of the Fc receptor-like 3 (FCRL3) gene in alopecia areata

A functional variant in the Fc receptor-like 3 (FCRL3) gene has been implicated in susceptibility to autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus and autoimmune thyroid disease. Investigating a large case-control sample of patients with alopecia areata (AA), we found no evidence for the involvement of FCRL3 in susceptibility to AA.

Investigation of the p.Ser278Arg polymorphism of the autoimmune regulator (AIRE) gene in alopecia areata

A recent study has suggested that the g.961C >G (p.Ser278Arg) variant of the autoimmune regulator (AIRE) gene contributes to susceptibility to alopecia areata (AA). We attempted to replicate this finding using a case-control sample of Belgian-German origin (273 patients and 283 controls). Despite adequate power, our study results do not support a significant association of the risk allele in our AA patient sample. This remained the case when we stratified our sample according to severity and family history of disease. Our study results do not support the hypothesis that the g.961C >G (p.Ser278Arg) polymorphism of the AIRE gene is associated with an increased risk for AA.

A non-sense mutation in the corneodesmosin gene in a Mexican family with hypotrichosis simplex of the scalp

BACKGROUND

Hypotrichosis simplex of the scalp (HSS; MIM 146520) is a rare autosomal dominant form of non-syndromic alopecia that affects men and women equally. Up to now, only a small number of families with HSS have been reported. The affected individuals experience a diffuse progressing hair loss from childhood to adulthood that is confined to the scalp. Recently, HSS has been mapped to the short arm of chromosome 6 (6p21.3), allowing mutations in the corneodesmosin gene (CDSN) to be identified as the cause of the disorder. To date, two stop mutations have been found in three unrelated families with HSS of different ethnic origin.

OBJECTIVES

To describe the first HSS-family with Latin American (Mexican) background comprising 6 generations and to identify a mutation in the CDSN gene.

PATIENTS/METHODS

The patients were examined by a clinician and blood samples were taken. After DNA extraction, sequencing analysis of the CDSN gene and restriction enzyme analysis with PsuI were performed.

RESULTS

By direct sequencing of the two exons of the CDSN gene, a nonsense mutation was identified in the index patient in exon 2, resulting in a premature stop codon (Y239X). The mutation co-segregates perfectly in the family with the disease and was not found in 300 control chromosomes using a restriction enzyme analysis with PsuI.

CONCLUSIONS

A nonsense mutation was identified in the first family with HSS of Latin American ethnical background. Our data provide molecular genetic evidence for a 3rd stop mutation in exon 2 of the CDSN gene being responsible for HSS. All to date known nonsense mutations responsible 3 for HSS are clustered in a region of 40 amino acids which is in accordance with a dominant negative effect conferred by aggregates of truncated CDSN proteins.

The hairless gene in androgenetic alopecia: results of a systematic mutation screening and a family-based association approach

BACKGROUND

Genetic disposition and androgen dependence are important characteristics of the common patterned loss of scalp hair known as androgenetic alopecia (AGA). The genetic factors contributing to AGA are currently unknown. The human hairless gene (HR) has recently been cloned and mutations have been reported in families with autosomal recessive universal congenital alopecia and papular atrichia. The main feature of these disorders is persistent complete absence of hair at or shortly after birth. This suggests that HR is essential and specific for the development of hair.

OBJECTIVES

To test the hypothesis that HR may be involved in AGA.

METHODS

We systematically screened HR for genetic variability by means of single-strand conformation analysis (SSCA) in 46 unrelated men with AGA. To test for an involvement of HR in the development of AGA, seven common variants were genotyped in 61 families with 93 affected offspring. The results were analysed with the transmission/disequilibrium test (TDT).

RESULTS

SSCA showed 15 single nucleotide substitutions: eight missense mutations, four silent mutations and three mutations in exon-flanking intronic sequences. TDT results showed a marginally significant association between AGA and variants 3379-29G/T (P = 0.024) and 2611-68C/T (P = 0.047). These results, however, did not remain significant after applying the conservative Bonferroni correction for multiple testing.

CONCLUSIONS

Our results do not provide evidence for a strong involvement of HR in the development of AGA, although a minor role cannot be fully excluded.

Mutations in CAV3 cause mechanical hyperirritability of skeletal muscle in rippling muscle disease

Hereditary rippling muscle disease (RMD) is an autosomal dominant human disorder characterized by mechanically triggered contractions of skeletal muscle. Genome-wide linkage analysis has identified an RMD locus on chromosome 3p25. We found missense mutations in positional candidate CAV3 (encoding caveolin 3; ref. 5) in all five families analyzed. Mutations in CAV3 have also been described in limb-girdle muscular dystrophy type 1C (LGMD1C; refs. 6,7), demonstrating the allelism of dystrophic and non-dystrophic muscle diseases.

A gene for hypotrichosis simplex of the scalp maps to chromosome 6p21.3

Hypotrichosis simplex of the scalp (HSS) is an autosomal dominant form of isolated alopecia causing almost complete loss of scalp hair, with onset in childhood. After exclusion of candidate regions previously associated with hair-loss disorders, we performed a genomewide linkage analysis in two Danish families and localized the gene to chromosome 6p21.3. This was confirmed in a Spanish family, with a total LOD score of 11.97 for marker D6S1701 in all families. The combined haplotype data identify a critical interval of 14.9 cM between markers D6S276 and D6S1607. Localization of the locus for HSS to 6p21.3 is a first step toward identification of the gene. The gene will give important insights into the molecular and cellular basis of hair growth on the scalp.