A large duplication in LIPH underlies autosomal recessive hypotrichosis simplex in four Middle Eastern families

The biology and genetics of curly hair

Hair fibres show wide diversity across and within all human populations, suggesting that hair fibre form and colour have been subject to much adaptive pressure over thousands of years. All human hair fibres typically have the same basic structure. However, the three-dimensional shape of the entire fibre varies considerably depending on ethnicity and geography, with examples from very straight hair with no rotational turn about the long axis, to the tightly sprung coils of African races. The creation of the highly complex biomaterials in hair follicle and how these confer mechanical functions on the fibre so formed is a topic that remains relatively unexplained thus far. We review the current understanding on how hair fibres are formed into a nonlinear coiled form and which genetic and biological factors are thought to be responsible for hair shape. We report on a new GWAS comparing low and high curl individuals in South Africa, revealing strong links to polymorphic variation in trichohyalin, a copper transporter protein CUTC and the inner root sheath component keratin 74. This builds onto the growing knowledge base describing the control of curly hair formation.

LIPH expression in skin and hair follicles of normal coat and Rex rabbits

Natural mutations in the LIPH gene were shown to be responsible for hair growth defects in humans and for the rex short hair phenotype in rabbits. In this species, we identified a single nucleotide deletion in LIPH (1362delA) introducing a stop codon in the C-terminal region of the protein. We investigated the expression of LIPH between normal coat and rex rabbits during critical fetal stages of hair follicle genesis, in adults and during hair follicle cycles. Transcripts were three times less expressed in both fetal and adult stages of the rex rabbits than in normal rabbits. In addition, the hair growth cycle phases affected the regulation of the transcription level in the normal and mutant phenotypes differently. LIPH mRNA and protein levels were higher in the outer root sheath (ORS) than in the inner root sheath (IRS), with a very weak signal in the IRS of rex rabbits. In vitro transfection shows that the mutant protein has a reduced lipase activity compared to the wild type form. Our results contribute to the characterization of the LIPH mode of action and confirm the crucial role of LIPH in hair production.

Unveiling the roots of monogenic genodermatoses: genotrichoses as a paradigm

The past two decades have seen significant and unprecedented progress in human genetics owing to the advent of novel molecular biological technologies and major developments in computational methods. Dermatology has benefited from and, in some cases, led these advances. In this article, we review major discoveries in the field of inherited hair diseases, which illustrate the changes that genodermatology has undergone in recent years from a mostly descriptive discipline through the elucidation of the molecular basis of numerous disorders, up to the first attempts at translating these new findings into novel preventive and therapeutic tools to the benefit of our patients.

A deletion in exon 9 of the LIPH gene is responsible for the rex hair coat phenotype in rabbits (Oryctolagus cuniculus)

The fur of common rabbits is constituted of 3 types of hair differing in length and diameter while that of rex animals is essentially made up of amazingly soft down-hair. Rex short hair coat phenotypes in rabbits were shown to be controlled by three distinct loci. We focused on the “r1” mutation which segregates at a simple autosomal-recessive locus in our rabbit strains. A positional candidate gene approach was used to identify the rex gene and the corresponding mutation. The gene was primo-localized within a 40 cM region on rabbit chromosome 14 by genome scanning families of 187 rabbits in an experimental mating scheme. Then, fine mapping refined the region to 0.5 cM (Z = 78) by genotyping an additional 359 offspring for 94 microsatellites present or newly generated within the first defined interval. Comparative mapping pointed out a candidate gene in this 700 kb region, namely LIPH (Lipase Member H). In humans, several mutations in this major gene cause alopecia, hair loss phenotypes. The rabbit gene structure was established and a deletion of a single nucleotide was found in LIPH exon 9 of rex rabbits (1362delA). This mutation results in a frameshift and introduces a premature stop codon potentially shortening the protein by 19 amino acids. The association between this deletion and the rex phenotype was complete, as determined by its presence in our rabbit families and among a panel of 60 rex and its absence in all 60 non-rex rabbits. This strongly suggests that this deletion, in a homozygous state, is responsible for the rex phenotype in rabbits.

Identification of 736T>A mutation of lipase H in Japanese siblings with autosomal recessive woolly hair

Woolly hair is characterized by fine and tightly curled hair. It has recently been revealed that both LPAR6 and lipase H (LIPH) mutations cause autosomal recessive woolly hair (ARWH)/hypotrichosis. This notion has provided critical evidence to the concept that LPA6 activation by LIPH-catalyzed lipid mediator lysophosphatidic acid has a key role in regulation of hair follicle development. Very recently, novel mutations in exon 6, homozygous 736T>A and compound heterozygous 736T>A and 742C>A have been identified in Japanese ARWH/hypotrichosis patients. Here, we report on siblings (a 7-year-old Japanese girl and her 5-year-old brother) both showing woolly hair. Determination of their genomic sequence showed presence of a homozygous 736T>A transition in exon 6 of the LIPH gene changing cysteine at position 246 to serine, without any mutation in the LPAR6 gene. Additionally, the same mutation was found in one out of a 100 alleles of Japanese healthy controls and identified homozygously in three out of four other Japanese sporadic cases with woolly hair. Collectively, it has been suggested that 736T>A transition is highly specific and common in ARWH/hypotrichosis of Japanese origin.

A novel mutation in LPAR6 causes autosomal recessive hypotrichosis of the scalp

BACKGROUND

Autosomal recessive hypotrichosis simplex (ARHS) presents with progressive hair loss mainly affecting the scalp area. In a small number of families, the condition has been associated with mutations in three distinct genes: DSG4, LIPH and LPAR6.

AIM

To identify the molecular basis of ARHS in a consanguineous family of Turkish extraction.

METHODS

We used a combination of microsatellite marker screening and direct sequencing.

RESULTS

We identified a novel missense mutation (c.C587T) in the human LPAR6 gene, resulting in the amino acid substitution p.P196L. The mutation affects a highly conserved amino acid residue, and is predicted to disrupt signalling through the P2Y5 receptor.

CONCLUSIONS

This study provides further evidence supporting a role for the lysophosphatidyl signalling pathway in hair growth and differentiation. In addition, this paper reports, for the first time to our knowledge, the use of homozygosity mapping as a premutation screening tool in the diagnosis of a group of inherited hair disorders.

Prevalent LIPH founder mutations lead to loss of P2Y5 activation ability of PA-PLA1alpha in autosomal recessive hypotrichosis

Autosomal recessive hypotrichosis (ARH) is characterized by sparse hair on the scalp without other abnormalities. Three genes, DSG4, LIPH, and LPAR6 (P2RY5), have been reported to underlie ARH. We performed a mutation search for the three candidate genes in five independent Japanese ARH families and identified two LIPH mutations: c.736T>A (p.Cys246Ser) in all five families, and c.742C>A (p.His248Asn) in four of the five families. Out of 200 unrelated control alleles, we detected c.736T>A in three alleles and c.742C>A in one allele. Haplotype analysis revealed each of the two mutant alleles is derived from a respective founder. These results suggest the LIPH mutations are prevalent founder mutations for ARH in the Japanese population. LIPH encodes PA-PLA(1)alpha (LIPH), a membrane-associated phosphatidic acid-preferring phospholipase A(1)alpha. Two residues, altered by these mutations, are conserved among PA-PLA(1)alpha of diverse species. Cys(246) forms intramolecular disulfide bonds on the lid domain, a crucial structure for substrate recognition, and His(248) is one amino acid of the catalytic triad. Both p.Cys246Ser- and p.His248Asn-PA-PLA(1)alpha mutants showed complete abolition of hydrolytic activity and had no P2Y5 activation ability. These results suggest defective activation of P2Y5 due to reduced 2-acyl lysophosphatidic acid production by the mutant PA-PLA(1)alpha is involved in the pathogenesis of ARH.

In vitro analysis of LIPH mutations causing hypotrichosis simplex: evidence confirming the role of lipase H and lysophosphatidic acid in hair growth

Hypotrichosis simplex (HS) is a group of isolated alopecias that can be inherited as an autosomal-dominant or an autosomal-recessive trait. Hair loss usually begins in early childhood, and is diffuse and progressive. Mutations in LIPH, which encodes lipase member H, have recently been shown to cause an autosomal-recessive form of HS. Here we describe an Austrian HS patient who was found to be carrying compound heterozygous mutations in the LIPH gene: a 7-bp frameshift duplication (c.403_409dup; p.Gln137HisfsX1) and a recently reported 30-amino acid in-frame duplication (c.280_369dup; p.Gly94_Lys123dup). To examine the impact of LIPH mutations on lipid metabolism, we established an in vitro assay to measure the action of this phospholipase in a cell-based system. Both the 7-bp duplication frameshift mutation and all known in-frame mutations were observed to reduce the in vitro activity of the lipase in response to the addition of phosphatidic acid, the substrate of lipase H. The reduced production of lysophosphatidic acid (LPA) led to a reduced response of cells expressing the human G-protein-coupled receptor p2y5 (p2y5) receptor. Our study increases the spectrum of known LIPH mutations and provides biochemical evidence for the important role of lipase H and its product LPA in human hair growth.

Identification and characterization of a novel lysophosphatidic acid receptor, p2y5/LPA6

p2y5 is an orphan G protein-coupled receptor that is closely related to the fourth lysophosphatidic acid (LPA) receptor, LPA4. Here we report that p2y5 is a novel LPA receptor coupling to the G13-Rho signaling pathway. "LPA receptor-null" RH7777 and B103 cells exogenously expressing p2y5 showed [3H]LPA binding, LPA-induced [35S]guanosine 5'-3-O-(thio)triphosphate binding, Rho-dependent alternation of cellular morphology, and Gs/13 chimeric protein-mediated cAMP accumulation. LPA-induced contraction of human umbilical vein endothelial cells was suppressed by small interfering RNA knockdown of endogenously expressed p2y5. We also found that 2-acyl-LPA had higher activity to p2y5 than 1-acyl-LPA. A recent study has suggested that p2y5 is an LPA receptor essential for human hair growth. We confirmed that p2y5 is a functional LPA receptor and propose to designate this receptor LPA6.

Founder mutations in the lipase h gene in families with autosomal recessive woolly hair/hypotrichosis

Autosomal-recessive woolly hair (ARWH)/hypotrichosis is a hereditary hair disorder which is characterized by tightly curled hair and is associated with sparse hair. ARWH can be caused by mutations in the P2RY5 or lipase H (LIPH) gene. Disruption of either gene results in phenotypes with features of both wooly hair (WH) and hypotrichosis. In this study, we identified two Guyanese families with ARWH. Both families are of recent Indian descent. Mutation analysis resulted in the identification of mutations in the LIPH gene in both families. Affected individuals in the first family carry compound heterozygous mutations Ex7_8del and 1303_1309dupGAAAACG in the LIPH gene, while those in the second family have a homozygous mutation 659_660delTA in the LIPH gene. The mutations Ex7_8del and 659_660delTA were identified earlier in several Pakistani families with ARWH. Haplotype analysis using microsatellite markers close to the LIPH gene defined a founder haplotype shared in families from Pakistan and Guyana. Proteomic analysis of hair shaft samples from one of the families revealed no substantial changes among the proteins identified, indicating that the syndrome does not involve global alterations in protein expression. Our results further suggest a crucial role of LIPH gene in hair growth.