DISEASE CARD

Definition

Short Anagen Syndrome (SAS) is a rare, primarily pediatric hair growth disorder characterized by an abnormally short anagen (growth) phase of the hair cycle. As a result, scalp hair remains short and does not require cutting.

Clinical Description

Short Anagen Syndrome (SAS) is a rare, primarily pediatric hair growth disorder. It typically presents between the ages of 2 and 4, with parents reporting that their child’s hair has never needed a haircut. The hair is short, fine, and sparse, but the scalp appears normal, without signs of inflammation or scarring. Other ectodermal structures such as teeth, nails, and skin are unaffected. Most cases are sporadic, although a rare familial case with autosomal dominant inheritance has been described. The condition is benign but can cause psychosocial distress, especially in young girls.

Pathogenesis

The disorder is characterized by an abnormally short anagen (growth) phase of the hair cycle, typically lasting only 4 to 13 months (compared to the normal 2 to 7 years). As a result, hair does not grow beyond a certain length.

The underlying mechanisms are likely genetic but have not yet been fully elucidated. In 40%, alterations in the WNT10A gene have been identified as the cause. Individuals with one or two changes in WNT10A develop SAH, and mostly have blonde hair and a high frontal hairline with what is called frontoparietal recession of the hairline (that is, affecting areas at the front and top). Males who have SAH-related WNT10A changes have an increased risk of developing male pattern hair loss.

Diagnosis

Diagnosis is primarily clinical and supported by non-invasive and semi-invasive tests:

• History: Hair never requires cutting; slow or absent growth since infancy.

• Hair card test: Shows short hairs with conical (tapered) tips.

• Pull test: Often negative or mildly positive, extracting short telogen hairs.

• Trichoscopy: Reveals hair shafts of varying diameters; 10–20% of shafts are thinner than 60 µm.

• Trichogram: Shows a decreased anagen-to-telogen ratio (~66:34, compared to the normal 90:10).

Differentialdiagnosis

SAS must be differentiated from other pediatric hair disorders:

• Loose Anagen Hair Syndrome (LAHS): Easily extractable anagen hairs; positive pull test with anagen roots lacking root sheaths.

• Diffuse Alopecia Areata: Hair loss with thinning; trichoscopy shows yellow dots, black dots, and exclamation/broken hairs.

• Telogen Effluvium: Triggered by systemic factors; pull test positive for telogen roots; trichoscopy shows regrowing upright hairs.

• Hereditary Hypotrichoses and Ectodermal Dysplasias: Often associated with abnormalities in teeth, nails, or skin, which are absent in SAS.

Treatment

There is no standardized treatment, as SAS often improves spontaneously after puberty. However, interventions can support hair growth:

Biotin (5 mg/day): Well tolerated and effective in improving hair density and shaft diameter.

Topical Minoxidil (2%): Used in cases of insufficient response to biotin. It prolongs the anagen phase and promotes growth.

The prognosis is favorable; most children show improvement over time. SAS may have strong psychologic, emotional and social impacts on affected children and their caregivers.

References