We have conducted a multistage genomewide association study, using 1,620,742 single-nucleotide polymorphisms to systematically investigate the genetic factors influencing intrinsic skin pigmentation in a population of South Asian descent. Polymorphisms in three genes--SLC24A5, TYR, and SLC45A2--yielded highly significant replicated associations with skin-reflectance measurements, an indirect measure of melanin content in the skin. The associations detected in these three genes, in an additive manner, collectively account for a large fraction of the natural variation of skin pigmentation in a South Asian population. Our study is the first to interrogate polymorphisms across the genome, to find genetic determinants of the natural variation of skin pigmentation within a human population.

The desire of many to look young for their age has led to the establishment of a large cosmetics industry. However, the features of appearance that primarily determine how old women look for their age and whether genetic or environmental factors predominately influence such features are largely unknown. We studied the facial appearance of 102 pairs of female Danish twins aged 59 to 81 as well as 162 British females aged 45 to 75. Skin wrinkling, hair graying and lip height were significantly and independently associated with how old the women looked for their age. The appearance of facial sun-damage was also found to be significantly correlated to how old women look for their age and was primarily due to its commonality with the appearance of skin wrinkles. There was also considerable variation in the perceived age data that was unaccounted for. Composite facial images created from women who looked young or old for their age indicated that the structure of subcutaneous tissue was partly responsible. Heritability analyses of the appearance features revealed that perceived age, pigmented age spots, skin wrinkles and the appearance of sun-damage were influenced more or less equally by genetic and environmental factors. Hair graying, recession of hair from the forehead and lip height were influenced mainly by genetic factors whereas environmental factors influenced hair thinning. These findings indicate that women who look young for their age have large lips, avoid sun-exposure and possess genetic factors that protect against the development of gray hair and skin wrinkles. The findings also demonstrate that perceived age is a better biomarker of skin, hair and facial aging than chronological age.

To help elucidate the factors responsible for the infundibular changes seen in acne, the human sebaceous pilosebaceous infundibulum was isolated by microdissection and maintained for 7 d in keratinocyte serum-free medium supplemented with 50 micrograms/ml bovine pituitary extract, 100 units/ml penicillin and streptomycin, 2.5 micrograms/ml amphotericin B and CaCl2(10H2O) to give a final Ca2+ concentration of 2 mM. Infundibular structure was maintained over 7 d in this medium; the pattern of cell division mimicked that in vivo. The rate of cell division was significantly higher than previously described for infundibula maintained in supplemented William's E medium, and moreover did not fall over 7 d. The addition of 1 ng/ml interleukin-1 alpha (IL-1 alpha) caused hypercornification of the infundibulum similar to that seen in comedones; this could be blocked by 1000 ng/ml interleukin-1 receptor antagonist (IL-1ra). In about 20% of subjects there was spontaneous hypercornification of the infundibulum that could be blocked by 1000 ng/ml IL-1ra, suggesting that the infundibulum is capable of synthesising IL-1 alpha. The addition of 5 ng/ml epidermal growth factor or 5 ng/ml transforming growth factor-alpha to the medium caused a disorganisation of the keratinocytes of the infundibulum that resulted in rupturing similar to that seen in the more severe, purulent grades of acne. The addition of 1 microM 13-cis retinoic acid caused a significant reduction in the rate of DNA synthesis and apparent parakeratosis. We are now, therefore, able to model histologically the major infundibular changes in acne.

A non-synonymous single nucleotide polymorphism in the human SLC24A5 gene is associated with natural human skin color variation. Multiple sequence alignments predict that this gene encodes a member of the potassium-dependent sodium-calcium exchanger family denoted NCKX5. In cultured human epidermal melanocytes we show using affinity-purified antisera that native human NCKX5 runs as a triplet of approximately 43 kDa on SDS-PAGE and is partially localized to the trans-Golgi network. Removal of the NCKX5 protein through small interfering RNA-mediated knockdown disrupts melanogenesis in human and murine melanocytes, causing a significant reduction in melanin pigment production. Using a heterologous expression system, we confirm for the first time that NCKX5 possesses the predicted exchanger activity. Site-directed mutagenesis of NCKX5 and NCKX2 in this system reveals that the non-synonymous single nucleotide polymorphism in SLC24A5 alters a residue that is important for NCKX5 and NCKX2 activity. We suggest that NCKX5 directly regulates human epidermal melanogenesis and natural skin color through its intracellular potassium-dependent exchanger activity.