Regina C. Betz

G protein-coupled receptor P2Y5 and its ligand LPA are involved in maintenance of human hair growth

Hypotrichosis simplex is a group of nonsyndromic human alopecias. We mapped an autosomal recessive form of this disorder to chromosome 13q14.11–13q21.33, and identified homozygous truncating mutations in P2RY5, which encodes an orphan G protein–coupled receptor. Furthermore, we identified oleoyl-L-α-lysophosphatidic acid (LPA), a bioactive lipid, as a ligand for P2Y5 in reporter gene and radioligand binding experiments. Homology and studies of signaling transduction pathways suggest that P2Y5 is a member of a subgroup of LPA receptors, which also includes LPA4 and LPA5. Our study is the first to implicate a G protein–coupled receptor as essential for and specific to the maintenance of human hair growth. This finding may provide opportunities for new therapeutic approaches to the treatment of hair loss in humans.

Loss-of-Function Mutations in the Keratin 5 Gene Lead to Dowling-Degos Disease

Dowling-Degos disease (DDD) is an autosomal dominant genodermatosis characterized by progressive and disfiguring reticulate hyperpigmentation of the flexures. We performed a genomewide linkage analysis of two German families and mapped DDD to chromosome 12q, with a total LOD score of 4.42 ( theta =0.0) for marker D12S368. This region includes the keratin gene cluster, which we screened for mutations. We identified loss-of-function mutations in the keratin 5 gene (KRT5) in all affected family members and in six unrelated patients with DDD. These represent the first identified mutations that lead to haploinsufficiency in a keratin gene. The identification of loss-of-function mutations, along with the results from additional functional studies, suggest a crucial role for keratins in the organization of cell adhesion, melanosome uptake, organelle transport, and nuclear anchorage.

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.

Genetic Variation in the Human Androgen Receptor Gene Is the Major Determinant of Common Early-Onset Androgenetic Alopecia

Androgenetic alopecia (AGA), or male-pattern baldness, is the most common form of hair loss. Its pathogenesis is androgen dependent, and genetic predisposition is the major requirement for the phenotype. We demonstrate that genetic variability in the androgen receptor gene (AR) is the cardinal prerequisite for the development of early-onset AGA, with an etiological fraction of 0.46. The investigation of a large number of genetic variants covering the AR locus suggests that a polyglycine-encoding GGN repeat in exon 1 is a plausible candidate for conferring the functional effect. The X-chromosomal location of AR stresses the importance of the maternal line in the inheritance of AGA.

Hypotrichosis simplex of the scalp is associated with nonsense mutations in CDSN encoding corneodesmosin

We have identified nonsense mutations in the gene CDSN (encoding corneodesmosin) in three families suffering from hypotrichosis simplex of the scalp (HSS; OMIM 146520). CDSN, a glycoprotein expressed in the epidermis and inner root sheath (IRS) of hair follicles, is a keratinocyte adhesion molecule. Truncated CDSN aggregates were detected in the superficial dermis and at the periphery of hair follicles. Our findings suggest that CDSN is important in normal scalp hair physiology.

Loss-of-function mutations of an inhibitory upstream ORF in the human hairless transcript cause Marie Unna hereditary hypotrichosis

Marie Unna hereditary hypotrichosis (MUHH) is an autosomal dominant form of genetic hair loss. In a large Chinese family carrying MUHH, we identified a pathogenic initiation codon mutation in U2HR, an inhibitory upstream ORF in the 5′ UTR of the gene encoding the human hairless homolog (HR). U2HR is predicted to encode a 34–amino acid peptide that is highly conserved among mammals. In 18 more families from different ancestral groups, we identified a range of defects in U2HR, including loss of initiation, delayed termination codon and nonsense and missense mutations. Functional analysis showed that these classes of mutations all resulted in increased translation of the main HR physiological ORF. Our results establish the link between MUHH and U2HR, show that fine-tuning of HR protein levels is important in control of hair growth, and identify a potential mechanism for preventing hair loss or promoting hair removal.

The brain in myotonic dystrophy 1 and 2: evidence for a predominant white matter disease

Myotonic dystrophy types 1 and 2 are progressive multisystemic disorders with potential brain involvement. We compared 22 myotonic dystrophy type 1 and 22 myotonic dystrophy type 2 clinically and neuropsychologically well-characterized patients and a corresponding healthy control group using structural brain magnetic resonance imaging at 3 T (T(1)/T(2)/diffusion-weighted). Voxel-based morphometry and diffusion tensor imaging with tract-based spatial statistics were applied for voxel-wise analysis of cerebral grey and white matter affection (P(corrected) < 0.05). We further examined the association of structural brain changes with clinical and neuropsychological data. White matter lesions rated visually were more prevalent and severe in myotonic dystrophy type 1 compared with controls, with frontal white matter most prominently affected in both disorders, and temporal lesions restricted to myotonic dystrophy type 1. Voxel-based morphometry analyses demonstrated extensive white matter involvement in all cerebral lobes, brainstem and corpus callosum in myotonic dystrophy types 1 and 2, while grey matter decrease (cortical areas, thalamus, putamen) was restricted to myotonic dystrophy type 1. Accordingly, we found more prominent white matter affection in myotonic dystrophy type 1 than myotonic dystrophy type 2 by diffusion tensor imaging. Association fibres throughout the whole brain, limbic system fibre tracts, the callosal body and projection fibres (e.g. internal/external capsules) were affected in myotonic dystrophy types 1 and 2. Central motor pathways were exclusively impaired in myotonic dystrophy type 1. We found mild executive and attentional deficits in our patients when neuropsychological tests were corrected for manual motor dysfunctioning. Regression analyses revealed associations of white matter affection with several clinical parameters in both disease entities, but not with neuropsychological performance. We showed that depressed mood and fatigue were more prominent in patients with myotonic dystrophy type 1 with less white matter affection (early disease stages), contrary to patients with myotonic dystrophy type 2. Thus, depression in myotonic dystrophies might be a reactive adjustment disorder rather than a direct consequence of structural brain damage. Associations of white matter affection with age/disease duration as well as patterns of cerebral water diffusion parameters pointed towards an ongoing process of myelin destruction and/or axonal loss in our cross-sectional study design. Our data suggest that both myotonic dystrophy types 1 and 2 are serious white matter diseases with prominent callosal body and limbic system affection. White matter changes dominated the extent of grey matter changes, which might argue against Wallerian degeneration as the major cause of white matter affection in myotonic dystrophies.

IFAP Syndrome Is Caused by Deficiency in MBTPS2, an Intramembrane Zinc Metalloprotease Essential for Cholesterol Homeostasis and ER Stress Response

Ichthyosis follicularis with atrichia and photophobia (IFAP syndrome) is a rare X-linked, oculocutaneous human disorder. Here, we assign the IFAP locus to the 5.4 Mb region between DXS989 and DXS8019 on Xp22.11-p22.13 and provide evidence that missense mutations exchanging highly conserved amino acids of membrane-bound transcription factor protease, site 2 (MBTPS2) are associated with this phenotype. MBTPS2, a membrane-embedded zinc metalloprotease, activates signaling proteins involved in sterol control of transcription and ER stress response. Wild-type MBTPS2 was able to complement the protease deficiency in Chinese hamster M19 cells as shown by induction of an SRE-regulated reporter gene in transient transfection experiments and by growth of stably transfected cells in media devoid of cholesterol and lipids. These functions were impaired in five mutations as detected in unrelated patients. The degree of diminished activity correlated with clinical severity as noted in male patients. Our findings indicate that the phenotypic expression of IFAP syndrome is quantitatively related to a reduced function of a key cellular regulatory system affecting cholesterol homeostasis and ability to cope with ER stress.

Mutations in POGLUT1, Encoding Protein O-Glucosyltransferase 1, Cause Autosomal-Dominant Dowling-Degos Disease

Dowling-Degos disease (DDD) is an autosomal-dominant genodermatosis characterized by progressive and disfiguring reticulate hyperpigmentation. We previously identified loss-of-function mutations in KRT5 but were only able to detect pathogenic mutations in fewer than half of our subjects. To identify additional causes of DDD, we performed exome sequencing in five unrelated affected individuals without mutations in KRT5. Data analysis identified three heterozygous mutations from these individuals, all within the same gene. These mutations, namely c.11G>A (p.Trp4*), c.652C>T (p.Arg218*), and c.798-2A>C, are within POGLUT1, which encodes protein O-glucosyltransferase 1. Further screening of unexplained cases for POGLUT1 identified six additional mutations, as well as two of the above described mutations. Immunohistochemistry of skin biopsies of affected individuals with POGLUT1 mutations showed significantly weaker POGLUT1 staining in comparison to healthy controls with strong localization of POGLUT1 in the upper parts of the epidermis. Immunoblot analysis revealed that translation of either wild-type (WT) POGLUT1 or of the protein carrying the p.Arg279Trp substitution led to the expected size of about 50 kDa, whereas the c.652C>T (p.Arg218*) mutation led to translation of a truncated protein of about 30 kDa. Immunofluorescence analysis identified a colocalization of the WT protein with the endoplasmic reticulum and a notable aggregating pattern for the truncated protein. Recently, mutations in POFUT1, which encodes protein O-fucosyltransferase 1, were also reported to be responsible for DDD. Interestingly, both POGLUT1 and POFUT1 are essential regulators of Notch activity. Our results furthermore emphasize the important role of the Notch pathway in pigmentation and keratinocyte morphology.

Genome-wide meta-analysis in alopecia areata resolves HLA associations and reveals two new susceptibility loci

Alopecia areata (AA) is a prevalent autoimmune disease with ten known susceptibility loci. Here we perform the first meta-analysis in AA by combining data from two genome-wide association studies (GWAS), and replication with supplemented ImmunoChip data for a total of 3,253 cases and 7,543 controls. The strongest region of association is the MHC, where we fine-map 4 independent effects, all implicating HLA-DR as a key etiologic driver. Outside the MHC, we identify two novel loci that exceed statistical significance, containing ACOXL/BCL2L11(BIM) (2q13); GARP (LRRC32) (11q13.5), as well as a third nominally significant region SH2B3(LNK)/ATXN2 (12q24.12). Candidate susceptibility gene expression analysis in these regions demonstrates expression in relevant immune cells and the hair follicle. We integrate our results with data from seven other autoimmune diseases and provide insight into the alignment of AA within these disorders. Our findings uncover new molecular pathways disrupted in AA, including autophagy/apoptosis, TGFß/Tregs and JAK kinase signaling, and support the causal role of aberrant immune processes in AA.