Dermatologists employ the term hypotrichosis to characterize a state of absent hair growth. Unlike alopecia, which denotes the loss of hair where it once existed, hypotrichosis signifies a lack of initial hair growth. Hypotrichoses, in plural, thus denote conditions present from birth, often persisting throughout one’s life.
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The primary causes of hypotrichoses typically stem from genetic anomalies or disruptions in embryonic development, encompassing numerous genetic variations. Frequently, those affected may also contend with additional physical or cognitive challenges alongside the absence of hair. Syndromes such as Graham-Little syndrome, Ofuji syndrome, cartilage-hair hypoplasia, Jeanselme and Rime hypotrichosis, Marie Unna hypotrichosis, and metaphyseal chondrodysplasia, among others, may manifest hypotrichosis as a symptom.
Advancements in understanding the human genome have led to increased comprehension of the mechanisms by which genetic anomalies induce hair loss and associated symptoms. However, while the genetics and biochemistry underlying hypotrichoses are becoming clearer, effective treatments remain elusive, with most conditions lacking known remedies.
Certain forms of hypotrichosis merit attention due to their relative prevalence or their significance in elucidating the intricacies of hair follicle biology.
Congenital Aplasia
Congenital Aplasia, also known as aplasia cutis congenita, is a condition characterized by an incomplete formation of the skin during embryonic development, with the exact causes remaining unclear. This condition manifests as a newborn having a skin patch resembling an open wound or ulcer. Typically, the affected area is located at the posterior part of the scalp, within the central area of the hair’s natural growth pattern known as the “whorl pattern.” In cases where the defect is minor, the skin may scab over, leaving behind a scar.
In certain instances, aplasia cutis congenita occurs during fetal development, resulting in a noticeable absence of hair follicles on the scalp at birth. However, when a newborn presents with a sizable congenital aplasia, surgical intervention is often necessary to excise the affected region and close the skin. This procedure is usually performed promptly due to the potential risks of hemorrhage and infection associated with the open wound. Expedited healing of the defect is crucial for optimal outcomes.
Triangular Alopecia
Triangular Alopecia, also known as alopecia triangularis, resembles congenital aplasia but typically manifests from birth. It commonly impacts a triangular region of the skin and hair above the temples. The exact cause is uncertain, leading to the absence of hair follicle growth in this specific area for some individuals. Although infants do not exhibit open ulcers as seen in aplasia cutis congenita, the ultimate outcome is similar: a hairless patch. Surgical options involve either excising the affected area or transplanting hair follicles from other parts of the scalp.
Congenital Atrichia
Congenital atrichia, also known as papular atrichia, presents a distinctive pattern of hair loss, distinguished as the initial human hair loss disorder attributed to a singular gene anomaly. Although commonly classified as a form of hypotrichosis, its manifestation is not strictly adherent to this categorization. Individuals with congenital atrichia may initially appear with a full head of hair, akin to any typical newborn. However, during early childhood, they undergo complete hair loss, with no subsequent regrowth.
Ordinary hair follicles rely on intricate chemical interplay between two fundamental cell types: specialized keratinocytes forming the outer skin epithelium, and modified fibroblasts, known as dermal papilla cells. Sustaining this communication through biochemical signals is crucial for regulating hair growth and cycling. Close cellular proximity is imperative for maintaining this process, as neither cell type can independently stimulate hair growth without reciprocal signaling.
The precise mechanism underlying congenital atrichia remains incompletely elucidated; however, it appears that during the initial resting (telogen) phase of hair follicles in early childhood, a detachment occurs between the two cell types. While the epithelial cell component retreats, as expected during the follicular resting phase, the dermal papilla cells fail to accompany them, leading to their separation. Consequently, the dermal papilla cells are left isolated deep within the skin, distant from the epithelial cells required for communication. This disruption in cellular dialogue precludes the initiation of a new anagen growth phase, resulting in permanent hair loss. Although congenital atrichia exhibits a hereditary pattern and tends to run in families, sporadic occurrences can arise in embryos without familial history. Notably, some individuals diagnosed with alopecia universalis may, in fact, present with congenital atrichia instead.
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