ARTICLE
Auteur(s) :, Seonghyang Sohn, Joong Sun Lee, Eun-So Lee,
Kyeong Han Yoon, Hee Young
Kang*
Laboratory of Cell Biology, Department of Dermatology, Ajou
University School of Medicine, 5 Wonchon-dong, Paldal-ku,
Suwon, 442-721, Korea (South)
accepté le 30 Septembre 2003
Segmented heterochromia of the scalp hair is a pigmentary disorder
characterized by alternating dark and light segments on each hair
shaft. It is known to be associated with iron deficiency anemia.
Only four cases of the disease have been reported [1-4]. The
mechanism of alternating segmentation of hair shafts is not clear
yet. Agouti signaling protein (ASP) or cystein was suggested as a
factor concerning the alternating pigmentation (“agouti pattern”)
of hairs [5, 6]. But there has been no evidence that ASP or cystein
presented itself in high concentration in the hair follicles. The
purpose of this study was to observe the ultrastructure of the
diseased hair bulbs in order to understand the mechanism of the
hair color changes.
Materials and methods
Two black haired patients with segmented heterochromia of the scalp
hair were involved in this study. One was an 11-year old boy, who
had had the hair disease for 1 year and iron deficiency anemia
for 6 years [4]. The other was a 15-year old girl, who had had
the hair disease for 1 year. She also had iron deficiency
anemia of the unknown duration. Clinically black hairs and hairs
with alternating dark and light segments were intermingled on the
vertex of the both patients (( Figure 1 )). Under the
light microscope dark segments of the hairs had densely packed
black-pigmented granules while light segments had loosely arranged
black or brown-pigmented granules [4]. After iron replacement for
11 months both patients had recovered the black hair color.
Normal and diseased hair shafts and bulbs were taken from both
patients for transmission electron microscopy (TEM).
Results
Melanosomes in dark or light segments of hair shafts. In TEM, the
amount of cortical melanosomes decreased along the shaft from the
dark segment to the light segment (( Figure 2 )). In dark
segments, dense and homogeneous ellipsoidal melanosomes were noted,
which gave place to small and round melanosomes while the hair
shaft became lighter. The melanosomes observed in the dark segments
were identical with those in the normal hair shafts (data not
shown).
Melanosomes in hair bulbs. There were two groups of melanosomes
lined up on the matrix. One was composed of compact homogeneous
ellipsoidal melanosomes and the other was composed of melanosomes
with irregular sizes and shapes (( Figure 3 )).
Melanocytes and Langerhans cells in hair bulbs. Melanocytes were
rare and most were found near dermal papilla. They possessed dense
nuclei and few melanosomes in their cytoplasm (( Figure 4 )).
Langerhans cells were very few and were found close to melanocytes
in the outer root sheath of bulbs. They possessed Birbeck granules
but not melanosomes (( Figure 5 )).
Microorganisms in hair bulbs. Bacteria were present in the
dermis just by the hair bulb (( Figure 6 )).
Discussion
Segmented heterochromia is characterized by alternating dark and
light segments in each hair shaft. The mechanism of alternating
segmentation of hair shafts is unknown. ASP or cystein has been
suggested as a causative factor of the disease [5, 6].
On TEM melanosomes in dark segments seemed to be eumelanosomes,
which were dense and ovoid, numerous and uniform in size, whereas
melanosomes in light segments seemed to be either pheomelanosomes
or aborted eumelanosomes [1, 7]. These data suggest that the
alternating pattern of hair pigmentation may be due to the
alternative production of different kinds of melanosomes. Although
human melanocytes are known to produce only one type of melanosome
in vivo, some human melanocytes in hair follicles are thought to
produce both eumelanosomes and pheomelanosomes and the selective
loss of either melanosome may determine hair color [8, 9]. In
agouti mice follicular melanocytes produce eumelanosome or
pheomelanosome according to the activity of agouti signaling
protein [6, 10].
In this study two columns of melanosomes composed of different
kinds of melanosomes were found in the same area in hair bulbs.
This finding is very different from the white hairs of alopecia
areata, in which there was only one type of melanosomes in the hair
bulbs (data not shown). Although we could not demonstrate
melanocytes producing either column of melanosomes, it is clear
that different kinds of melanosomes are produced simultaneously in
each diseased hair follicle. Most melanocytes in hair bulbs seemed
to be under apoptosis, necrosis, or ‘dark cell transformation’ due
to the changes of the nuclei [11]. The changes of melanocytes may
be responsible for the production of abnormal melanosomes in the
diseased hairs.
A few Langerhans cell were found in the outer root sheath and
near dermal papilla in bulb areas. They had well developed Birbeck
granules but no melanin in their cytoplasm. In other words they
might be involved in some immune mechanisms rather than in
scavenging useless melanin as in normal hair cycles.
Unidentified microorganisms were found just outside of a hair
follicle. They might be there incidentally because segmented
heterochromia is not an inflammatory disease and the disease can be
treated with iron replacement without antibiotics.
In our study, to understand the pathogenesis of segmented
heterochromia, the ultrastructure of hair shaft and bulb was
observed. Recently studying the molecular genetics of hair follicle
has advanced [12]. So, the study based on the molecular level seems
to be another method to understand this disease in the future.
References
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