Two cases of severe congenital hypotrichosis caused by compound heterozygous mutations in the LSS gene

A novel LSS variant leading to hypotrichosis with pseudoainhum

Congenital alopecia/hypotrichosis constitutes a spectrum of rare inherited hair disorders characterized by partial to complete alopecia and possible structural hair shaft defects. The lanosterol synthase (LSS) gene, implicated in cholesterol biosynthesis, has emerged as a novel genetic determinant of congenital hypotrichosis. This article describes a 43-year-old female with congenital lanugo-like scalp hair and absence of eyebrows who later developed painful fibrotic constrictive bands on her fingers, culminating in pseudoainhum, but without manifestations of typical palmoplantar keratoderma (PPK). Whole-exome sequencing detected a novel homozygous variant (c.508G>A; p. Asp170Asn) in the LSS gene. This case delineates an atypical LSS variant presentation associated with pseudoainhum phenotype, manifesting without classic PPK features, a previously unreported phenotypic combination. Our findings expand the phenotypic spectrum of LSS-related disorders and underscore the potential role of lipid signaling in hair follicle biology and the pseudoainhum phenomenon.

Molecular Basis of Hereditary Hair Diseases

The hair follicle is an appendage of the skin that undergoes hair cycles throughout life. Recently, numerous genes expressed in the hair follicles have been identified, and variants in some of these genes are now known to underlie hereditary hair diseases in humans. Hereditary hair diseases are classified into non-syndromic and syndromic forms. In the Japanese population, the non-syndromic form of autosomal recessive woolly hair, which is caused by founder pathogenic variants in the lipase H (LIPH) gene, is the most prevalent hereditary hair disease. In addition, other types of hereditary hair diseases are known in Japan, such as Marie-Unna hereditary hypotrichosis, hypohidrotic ectodermal dysplasia, and tricho-rhino-phalangeal syndrome. To ensure correct diagnoses and appropriate patient care, dermatologists must understand the characteristics of each hair disorder. Elucidation of the molecular basis of hereditary hair diseases can directly tell us which genes are crucial for morphogenesis and development of hair follicles in humans. Therefore, continuation of "wet laboratory" research for these diseases remains important. To date, several syndromic forms of hereditary hair diseases have been approved as designated intractable diseases in Japan. As part of our efforts in the Project for Research on Intractable Diseases through the Ministry of Health, Labour, and Welfare of Japan, we anticipate that more hereditary hair diseases be recognized as designated intractable diseases in the future, which will be to the benefit of the affected individuals.

Biallelic pathogenic variants in the LSS gene cause congenital alopecia-cataract syndrome

Biallelic variants in the LSS gene have been reported in individuals affected by alopecia-intellectual disability syndrome 4, cataract 44, hypotrichosis 14, and palmoplantar keratoderma-congenital alopecia syndrome type 2. The present report described a Chinese girl with congenital alopecia universalis, cataract, esotropia, and nystagmus caused by compound heterozygous variants of c.1025T>G (p.Ile342Ser) and previously unreported c.1011G>A (p.Pro337=) in the LSS gene. Minigene assay confirmed the synonymous variant Pro337= at the edge of exon 9 could produce a novel splice site, leading to a 46-bp insertion of the 5' sequence of the intron 9, likely resulting in a frameshift effect. We consider that the clinical manifestations of this case represent a new type of LSS-related disease, namely congenital alopecia-cataract syndrome (CACS). Our data expand the phenotypic and genetic spectrum of LSS-related diseases.

Novel LSS variants in alopecia and intellectual disability syndrome: New case report and clinical spectrum of LSS-related rare disease traits

Pathogenic biallelic variants in LSS are associated with three Mendelian rare disease traits including congenital cataract type 44, autosomal recessive hypotrichosis type 14, and alopecia-intellectual disability syndrome type 4 (APMR4). We performed trio research exome sequencing on a family with a four-year-old male with global developmental delay, epilepsy and striking alopecia, and identified novel compound heterozygous LSS splice site (c.14+2T>C) and missense (c.1357 G>A; p.V453L) variant alleles. Rare features associated with APMR4 such as cryptorchidism, micropenis, mild cortical brain atrophy and thin corpus callosum were detected. Previously unreported APMR4 findings including cerebellar involvement in the form of unsteady ataxic gait, small vermis with prominent folia, were noted. A review of all reported variants to date in 29 families with LSS-related phenotypes showed an emerging genotype-phenotype correlation. Our report potentially expands LSS-related phenotypic spectrum and highlights the importance of performing brain imaging in LSS-related conditions.

A novel homozygous mutation in LSS gene possibly causes hypotrichosis simplex in two siblings of a Tibetan family from the western Sichuan province of China

Aim: Hypotrichosis simplex (MIM 146520) is a rare form of monogenic hereditary alopecia. Several genes have been identified as being associated with the disease, including LPAR6, LIPH, and DSG4. LSS encoding lanosterol synthase (LSS) has been shown to cause hypotrichosis simplex, but the related mechanisms have not been elucidated to date. This study aims to find mutations in LSS from a Chinese family, among which a 21-year-old male patient and his 9-year-old sister were affected by hypotrichosis simplex. Methods: Dermoscopy and histological analysis were used to examine patients' scalps, while exome sequencing was used to find the mutations in LSS. Results: The hair loss was only detected on the scalp of the proband and his sister, while other ectodermal structures were normal with no systemic abnormalities. Further, the exome sequencing identified a new homozygous mutation NM_002340.6 (LSS_v001):c.812T>C (p.(Ile271Thr)) in the LSS gene of the proband, which was also found in his sister. In addition, a heterozygous mutation of LSS was found in their asymptomatic parents. Finally, the possible protein structure of the mutational LSS was predicted. Conclusion: The hypotrichosis simplex reported here could be an autosomal recessive disease in this family. The mutation on LSS might reduce the enzyme activity of LSS, thus leading to the disease.

Update of recent findings in genetic hair disorders

Genetic hair disorders, although unusual, are not very rare, and dermatologists often have opportunities to see patients. Significant advances in molecular genetics have led to identifying many causative genes for genetic hair disorders, including the recently identified causative genes, such as LSS and C3ORF52. Many patients have been detected with autosomal recessive woolly hair/hypotrichosis in the Japanese population caused by founder mutations in the LIPH gene. Additionally, many patients with genetic hair disorders caused by other genes have been reported in East Asia including Japan. Understanding genetic hair disorders is essential for dermatologists, and the findings obtained from analyzing these diseases will contribute to revealing the mechanisms of hair follicle morphogenesis and development in humans.