Aarskog-Scott Syndrome: Causes and Features

Aarskog-Scott syndrome is caused by mutations in a gene called FGD1, located on the X chromosome. Because of this inheritance pattern, the condition overwhelmingly affects boys and men, while mothers who carry the mutation typically show few or no signs. The syndrome’s hallmark is a distinctive combination of facial, skeletal, and genital differences that become apparent in early childhood, alongside short stature that can persist into adulthood. While the condition is rare, its features overlap with several other genetic syndromes, which means getting the right diagnosis often requires genetic testing.

What the FGD1 Gene Does and Why Mutations Matter

The FGD1 gene provides instructions for making a protein that acts as a molecular switch, turning on a signaling molecule called Cdc42. Cdc42 belongs to a family of proteins that help cells carry out basic tasks like migrating, dividing, and organizing their internal structures. When FGD1 works properly, this signaling chain guides the formation of bone and cartilage during embryonic development and continues to play a role in bone growth after birth.¹

When FGD1 is mutated, the protein either does not get made or does not work correctly. The downstream signaling that shapes bones, especially in the face, hands, and spine, goes awry. Studies in animal models have shown that FGD1 is expressed specifically in developing skeletal tissue, which explains why the syndrome’s effects are concentrated in bone and cartilage rather than, say, the heart or kidneys.² Researchers still do not fully understand every step between a broken FGD1 protein and the specific bone abnormalities seen in patients. Mouse studies have identified at least one intermediate signaling molecule called MLK3 that appears to sit between FGD1 and the final effects on bone, but the full pathway remains an active area of investigation.³

How It Is Inherited

Because FGD1 sits on the X chromosome, Aarskog-Scott syndrome follows an X-linked recessive inheritance pattern. Boys and men have only one X chromosome, so a single mutated copy of FGD1 is enough to cause the full syndrome. Girls and women have two X chromosomes, so a working copy on the second X can compensate for the faulty one. Carrier mothers may show very mild features, such as a slightly rounded face or a widow’s peak hairline, but they rarely have the full picture of the condition.

Family studies illustrate this clearly. In one report from China, two brothers in the same family both had the syndrome, having inherited the same FGD1 variant from their carrier mother.⁴ A mother who carries the mutation has a fifty-fifty chance of passing it to each son, which means affected brothers are not unusual. Daughters of a carrier mother have a fifty-fifty chance of becoming carriers themselves. Sporadic cases, where a new mutation arises for the first time in a child with no family history, also occur and can make the diagnosis less obvious initially.

It is worth noting that the condition is described as both genetically and clinically heterogeneous, meaning that different families carry different FGD1 mutations and those mutations can produce a range of severity.⁵ New FGD1 variants continue to be discovered; a recent study identified four previously unknown variants among just five patients.⁶ Some mutations knock out the protein entirely, while others leave it partially functional, which helps explain why the syndrome can range from subtle to severe even within the same family.

The Facial Appearance

The face is often where the syndrome is first noticed. Children with Aarskog-Scott syndrome tend to have widely spaced eyes, a feature known as hypertelorism, along with a broad forehead and a small, slightly upturned nose. The hairline often comes to a point in the center of the forehead, the classic widow’s peak. The midface can appear flat or underdeveloped, giving the face a rounded quality.

Around the eyes, drooping of the upper eyelids and downward-slanting eye openings are common.⁷ These features tend to become less pronounced with age. In many adults with the condition, the facial appearance can be fairly unremarkable to a casual observer, which is one reason the syndrome sometimes goes undiagnosed until a child’s short stature or other findings prompt a genetics evaluation. In some cases, though, severe craniofacial differences are present, particularly when the underlying FGD1 mutation has a large effect on protein function.⁸

Short Stature and Skeletal Findings

Short stature is one of the most consistent features. Growth tends to lag behind from early childhood, and final adult height is typically below average, though it varies. A study drawn from an international growth database found that the median height at the start of treatment was about 2.8 standard deviations below the mean for age, which roughly translates to being shorter than about 99 percent of same-age peers.⁹ Not every child with the syndrome is that far below average, but measurably short stature is the norm.

Beyond height, the skeleton shows a range of differences. Hands are often affected, with short, stubby fingers and unusual curvature of the fifth finger. Loose joints and a single crease across the palm have been described.¹⁰ The feet may also be broad and short. Some individuals have mild vertebral anomalies, though these are typically less dramatic than the vertebral problems seen in related conditions. The skeletal differences reflect FGD1’s role specifically in bone-forming tissue, as described earlier.

Genital Differences

The genital findings are part of the syndrome’s original description and one of the reasons it was historically called “faciogenital dysplasia.” In boys, the most distinctive feature is a fold of skin around the scrotum called a “shawl scrotum,” where scrotal tissue extends above and around the base of the penis. This finding is unusual enough that its presence in a short boy with a characteristic face strongly suggests the diagnosis.

Beyond the shawl scrotum, undescended testes are common and frequently require surgical correction. In the largest published series of adult and pediatric patients, nearly half required orchiopexy, the surgery to bring undescended testes into the scrotum.¹¹ Inguinal hernias and, less frequently, hypospadias (where the urethral opening is on the underside of the penis rather than the tip) are also reported. These findings matter for fertility. Some adult men with the syndrome have been found to have low or absent sperm counts, as documented in cases where men in their thirties and forties sought fertility evaluations.¹¹ Whether the fertility problems stem directly from the FGD1 mutation or from complications of undescended testes (which independently raise the risk of impaired sperm production) is not entirely clear.

Learning, Attention, and Intelligence

One of the most persistent misconceptions about Aarskog-Scott syndrome is that it causes intellectual disability. The largest clinical series to date, covering 111 male patients with confirmed FGD1 mutations, found that outright intellectual disability is rare. What is common, however, is a high rate of specific learning difficulties and attention deficit hyperactivity disorder (ADHD).¹² The distinction matters for families: a child with the syndrome is expected to have a normal IQ but may need educational support for attention or processing challenges.

An earlier study tested IQ in a group of affected individuals and found scores ranging from 68 to 128, following a normal bell curve. The researchers concluded that the syndrome does not lower average IQ.¹³ That said, the learning and attention difficulties reported in the larger series suggest that standard IQ testing may not capture the full picture. A child can have a perfectly average IQ and still struggle in a classroom if attention regulation, processing speed, or specific reading and math skills are affected. Early educational assessments and, when appropriate, behavioral interventions for ADHD can make a meaningful difference.

Eye and Dental Findings

The eyes are affected in several ways that go beyond the lid drooping and wide spacing already described. A study of affected family members documented patterns of misaligned eyes, involuntary eye movements, and amblyopia (sometimes called “lazy eye”). Other findings included farsightedness, significant astigmatism, and blue-tinged whites of the eyes.¹⁴ Not all of these appear in every patient, but the variety of eye problems means that regular ophthalmology visits are a standard part of managing the condition, particularly in young children whose visual system is still developing and where amblyopia can be treated most effectively.

The dental picture can also be complex. Jaw size and shape may be disproportionate, and some individuals are missing teeth entirely. A detailed review of three affected siblings found major dental and skeletal discrepancies in the jaw, along with congenitally missing teeth.⁷ Delayed eruption of teeth, crowding, and orthodontic issues are frequently reported in the broader literature as well. These dental features are not just cosmetic; bite problems and missing teeth can affect chewing and nutrition, making early dental evaluation and orthodontic planning worthwhile.

Growth Hormone Treatment

Because short stature is so central to the syndrome, growth hormone therapy has been investigated as a potential intervention. The results are encouraging, though not dramatic. In one study of 19 affected males, growth hormone treatment roughly doubled the growth rate, from about 4 centimeters per year to roughly 9 centimeters per year, and significantly improved standardized height scores. The benefit depended on how long treatment continued, how frequently injections were given, and how short the child was at the start.¹⁵

Data from a separate international growth database showed a similar pattern. After one year of treatment, median height improved from 2.8 to 2.3 standard deviations below average. After three years, it improved further to 1.8 standard deviations below average, and no adverse events were noted.⁹ Final adult height data from these cohorts are still limited, so it remains uncertain how much of the childhood gain persists. Growth hormone does not address the underlying FGD1 defect; it compensates for the growth deficit by providing a pharmacological boost to the growth plate. The decision to use it involves weighing the psychosocial benefits of improved height against the burden of daily or near-daily injections over several years.

Surgical Needs

Several features of Aarskog-Scott syndrome can benefit from or require surgical intervention. Undescended testes, hernias, and hypospadias are the most common surgical indications and follow the same timing and techniques used in children without the syndrome.¹⁶ Severe craniofacial deformities, when present, may require maxillofacial surgery, and dental anomalies often call for orthodontic treatment or prosthetic replacement of missing teeth.

Because so many organ systems can be involved, management tends to be multidisciplinary. A child with the syndrome might see a geneticist for diagnosis and counseling, an endocrinologist for growth concerns, an ophthalmologist for vision issues, a urologist for genital findings, and an orthodontist for dental alignment. Coordinating these visits can be challenging for families, but the individual treatments available are generally straightforward and well-established. The syndrome itself does not appear to increase surgical risk or complicate wound healing.

Conditions That Look Similar

Several other genetic syndromes share enough features with Aarskog-Scott syndrome to cause diagnostic confusion. Noonan syndrome is probably the most commonly considered alternative, since it also causes short stature, a characteristic facial appearance, and sometimes genital anomalies. Robinow syndrome shares the wide-spaced eyes, short stature, and genital hypoplasia, but tends to produce more prominent vertebral abnormalities such as fused or malformed vertebrae, as well as heart defects. SHORT syndrome, another look-alike, is distinguished by features like partial lipodystrophy (abnormal fat distribution), delayed teething, and specific eye abnormalities affecting the front chamber of the eye.¹⁷

The inheritance pattern helps narrow things down. Aarskog-Scott syndrome is X-linked, while Noonan syndrome is autosomal dominant (either parent can pass it on, and girls are affected as often as boys), and Robinow syndrome has both autosomal dominant and autosomal recessive forms. Still, clinical features alone are often insufficient, especially in young children where the phenotype is still evolving. Genetic testing through targeted gene panels or broader exome sequencing has become the standard way to confirm the diagnosis. A panel that includes FGD1 alongside genes for Noonan, Robinow, and other overlapping conditions can resolve the question in a single test.

How the Condition Changes with Age

Aarskog-Scott syndrome is not static. Many of the most recognizable facial features become less obvious as a child grows into adolescence and adulthood. The round face elongates, the widow’s peak may become less prominent, and the characteristic eye findings can soften. In a cohort that included adult patients up to age 49, some individuals had facial features subtle enough that clinicians who were not specifically looking for the syndrome might not notice anything unusual.¹¹

Short stature, on the other hand, generally persists. While pubertal growth spurts do occur, they may be delayed and tend not to fully close the height gap. The skeletal hand findings remain visible in adults but rarely cause functional limitations. The most consequential adult issue may be fertility. As noted earlier, some men with the syndrome have reduced or absent sperm production, and the combination of a history of undescended testes and the FGD1 mutation itself may contribute. Men with Aarskog-Scott syndrome who are considering starting families should be aware of this possibility and can discuss semen analysis with a reproductive specialist.

Getting a Diagnosis Today

Historically, Aarskog-Scott syndrome was diagnosed purely on clinical grounds, using criteria that required specific combinations of facial, skeletal, and genital findings. That approach had obvious limitations: mild cases were missed, and children with overlapping conditions were sometimes misdiagnosed. Genetic testing has transformed the diagnostic process. Identifying a pathogenic FGD1 variant confirms the diagnosis regardless of how many clinical features are present, and it provides certainty for family planning and carrier testing of female relatives.

The ongoing discovery of new FGD1 variants means that a negative genetic test does not completely rule out the syndrome. A variant of uncertain significance, where the gene change has not been seen before and its effect is unclear, can leave families in limbo. Functional studies, in which researchers test whether the variant actually disrupts the FGD1 protein’s activity, can help resolve ambiguous results but are not available in routine clinical labs.⁶ For families navigating an uncertain result, working with a genetics team experienced in skeletal dysplasias and RASopathies (the broader category of syndromes that affect growth-signaling pathways) offers the best chance of clarity.

1
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2
Developmental Dynamics. Skeletal-specific expression of Fgd1 during bone formation and skeletal defects in faciogenital dysplasia (FGDY; Aarskog syndrome)
3
JCI Insight. MLK3 regulates bone development downstream of the faciogenital dysplasia protein FGD1 in mice
4
PubMed Central. Case Report: Aarskog-scott syndrome caused by FGD1 gene variation: A family study
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PubMed Central. The Prevalence of Clinical Features in Patients with Aarskog-Scott Syndrome and Assessment of Genotype-Phenotype Correlation: A Systematic Review
6
SpringerLink / European Journal of Pediatrics. FGD1-related Aarskog-Scott syndrome: Identification of four novel variations and a literature review of clinical and molecular aspects
7
PubMed. Dental and Maxillofacial Signs in Aarskog Syndrome: A Review of 3 Siblings and the Literature
8
PubMed. Aarskog-Scott syndrome: a novel mutation in the FGD1 gene associated with severe craniofacial dysplasia
9
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10
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11
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12
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13
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14
PubMed. Ocular and systemic findings in the Aarskog (facial-digital-genital) syndrome
15
PubMed. The effect of growth hormone treatment on stature in Aarskog syndrome
16
PubMed Central. A novel frameshift mutation in the FGD1 gene causing Aarskog-Scott syndrome patient with hypogonadism: a case report
17
Annals of Clinical & Laboratory Science. The First Korean Family with Aarskog–Scott Syndrome Harboring a Novel Mutation in FGD1 Diagnosed via Targeted Gene Panel Sequencing