Serum insulin-like growth factor-1 concentrations are not reduced in Pomeranian dogs with Alopecia X: a case-control study

Abstract

Background

Alopecia X (AX)—also referred to as hair cycle arrest or Alopecia X-like syndrome—is a non-inflammatory disorder common in Pomeranians, though it frequently affects other breeds such as Alaskan Malamutes, Chow Chows, Schipperkes, and Poodles. Historically known by various names including growth hormone-responsive alopecia, castration-responsive alopecia and congenital adrenal hyperplasia-like syndrome, this condition represents a complex follicular arrest of “plush-coated” breeds.

The etiopathogenesis remains unclear, and reliable, minimally invasive diagnostic biomarkers are lacking. Insulin-like growth factor-1 (IGF-1) is essential for hair follicle cycling, and systemic deficiency has been hypothesized to contribute to canine alopecia. This study aimed to determine if serum IGF-1 concentrations differ between Pomeranian dogs with AX and healthy controls, and to evaluate the effect of neuter status on IGF-1 levels.

Results

Thirty client-owned Pomeranian dogs (11 AX, 19 healthy controls) were enrolled. Serum IGF-1 concentrations were measured via a human competitive ELISA kit validated in-house for canine samples. Data were non-normally distributed and analyzed via Mann-Whitney U tests. No significant difference in serum IGF-1 was detected between alopecic (median: 62.0 ng/mL; range: 7.31–151) and healthy dogs (median: 51.8 ng/mL; range: 7.43–209.76) (U = 74, p = 0.200). Neuter status was significantly imbalanced between groups (63.6% of cases neutered vs. 10.5% of controls, p = 0.002). While neutered dogs exhibited numerically higher mean IGF-1 values than intact dogs within the alopecic group, this difference was not statistically significant (p = 0.412). No correlation was found between IGF-1 and age or body weight.

Conclusions

Serum IGF-1 concentrations are not reduced in Pomeranian dogs with Alopecia X compared to healthy controls. Routine measurement of serum IGF-1 is not recommended as a diagnostic test for AX. The role of gonadectomy in modulating the GH/IGF-1 axis in this breed requires further investigation with larger, balanced cohorts.

Supplementary Information

The online version contains supplementary material available at https://doi.org/10.1186/s12917-026-05724-0.

Introduction

Alopecia X (AX)—historically recognized by various descriptors including hair cycle arrest and castration-responsive alopecia—is a non-inflammatory hair cycle disorder. While predominantly affecting adult Pomeranians, the condition is well-documented in other “plush-coated” breeds such as Alaskan Malamutes, Chow Chows, Schipperkes, and Miniature Poodles [1, 2]. Diagnosis remains a process of exclusion, relying on clinical presentation and histopathological evaluation to rule out classic endocrinopathies like hypothyroidism and hypercortisolism (Cushing’s syndrome) [2, 3].

Recent advances have shifted the understanding of AX from a simple hormonal deficiency to a complex, genetically programmed disorder. This was notably demonstrated by a cloned Pomeranian that developed AX at the same age as its genetic predecessor, regardless of surgical or environmental differences [4]. Mechanistically, research is now focused on follicular stem cell dysregulation. Specifically, downregulation of the Wnt/Shh pathways and decreased p63 immunoexpression in telogen and kenogen follicles suggest that a failure in the stem cell compartment is a primary driver of the hair cycle arrest [5, 6]. Additionally, recent epidemiological studies have identified male sex and a woolly coat type as significant phenotypic risk indicators for the development of the disease [7, 8].

Despite this shift toward local and genetic factors, the role of the systemic growth factor signaling axis remains a critical area of investigation. Insulin-like growth factor-1 (IGF-1) is a potent mitogen and anti-apoptotic factor for hair follicle keratinocytes, essential for anagen maintenance [9].

While systemic growth hormone (GH) and IGF-1 levels often fall within reference ranges in many affected dogs, the GH/IGF-1 axis may still function as a modulator of the local follicular environment or serve as a biomarker for subset populations [10]. Previous investigations into IGF-1 in alopecic dogs have yielded conflicting results, often due to small, heterogeneous breed samples [11].

Given the high breed-specific predisposition and the newly identified phenotypic markers in Pomeranians, further characterization of their systemic hormonal profile is warranted. The primary objective of this case-control study was to test the hypothesis that serum total IGF-1 concentrations are significantly lower in Pomeranian dogs with AX compared to age-matched healthy controls. A secondary objective was to explore the association between neuter status and serum IGF-1 levels within this specific breed population.

Methods

Study design and ethical approval

This prospective case-control study was approved by the Institutional Animal Care and Use Committee of Ferdowsi University of Mashhad (IACUC No: IR.UM.REC.1403.233; 15 March 2024). All procedures were performed in accordance with ARRIVE guidelines. Written informed owner consent was obtained for all animals.

Animals

A total of 30 purebred Pomeranian dogs presented to the Veterinary Teaching Hospital between April 2024 and June 2025 were enrolled.

Case group (n = 11). Inclusion criteria were: (1) presence of non-pruritic, non-inflammatory, bilaterally symmetric alopecia involving ≥ 2 body regions for > 3 months; (2) age > 6 months; (3) exclusion of other endocrinopathies. Exclusion criteria included: evidence of ectoparasites or dermatophytes on skin scraping/trichogram, systemic illness, administration of corticosteroids or sex hormones within 3 months, and diagnosis of primary hypothyroidism or hypercortisolism (Cushing’s syndrome) based on basal T4/TSH and ACTH stimulation test and/or low-dose dexamethasone suppression test, respectively. Dogs with low T4 and normal TSH were considered to have non-thyroidal illness syndrome and remained eligible for the study provided they lacked systemic signs of metabolic disease.

Control group (n = 19). Inclusion criteria were: (1) intact hair coat with no history of dermatological disease; (2) normal physical examination; (3) unremarkable CBC and serum biochemistry. Exclusion criteria were identical to the case group regarding systemic illness and medication history.

Sample collection and IGF-1 assay

Blood (5 mL) was collected via jugular or cephalic venipuncture into serum separator tubes. Samples were centrifuged at 1500 × g for 10 min within 1 h of collection. Serum was aliquoted and stored at -80 °C until analysis.

Serum IGF-1 concentrations were measured using a commercially available human competitive ELISA kit (LDN, Germany; Cat# EIA-4147) validated in-house for canine samples. The manufacturer reports 98% cross-reactivity with canine IGF-1. In-house validation demonstrated spike-and-recovery of 92.5% (range 88–106%) and dilutional linearity (R² = 0.98). All samples were assayed in duplicate. Intra- and inter-assay coefficients of variation were < 8% and < 12%, respectively. The detection limit was 0.8 ng/mL.

Statistical analysis

Data normality was assessed using Shapiro-Wilk tests. As IGF-1 concentrations were not normally distributed, non-parametric tests were employed. Comparisons between two groups (Case vs. Control; Intact vs. Neutered) were performed using the Mann-Whitney U test. Correlations between IGF-1 and continuous variables (age, weight) were assessed using Spearman’s rank correlation (ρ). Categorical variables (sex, neuter status) were analyzed using Fisher’s exact test. Statistical significance was set at p < 0.05 (two-tailed). Analyses were performed using SPSS v27 (IBM, USA).

Results

Population characteristics

The study population consisted of 30 Pomeranians. The case group (n = 11) and control group (n = 19) were well-matched for age (median 3.0 vs. 2.5 years, p = 0.156), weight (median 3.7 vs. 3.9 kg, p = 0.231), and sex distribution (female: male ratio 6:5 vs. 11:8, p = 0.483). Neuter status differed significantly between groups; 7/11 (63.6%) of alopecic dogs were neutered, compared to only 2/19 (10.5%) of healthy controls (Fisher’s exact test, p = 0.002).

Serum IGF-1 concentrations.

Serum IGF-1 concentrations were highly variable in both populations.

• - Controls: Mean ± SD: 52.71 ± 53.95 ng/mL; Median [IQR]: 51.8 [30.6–104.5]; Range: 7.43–209.76.

• - Cases: Mean ± SD: 56.92 ± 46.97 ng/mL; Median [IQR]: 62.0 [31.7–139.0]; Range: 7.31–151.

The difference between groups was not statistically significant (Mann-Whitney U = 74, p = 0.200) (Fig. 1).

Fig. 1.

Serum IGF-1 concentrations (ng/mL) in healthy control Pomeranians (n = 19) and Pomeranians with Alopecia X (n = 11). Horizontal lines represent median values; boxes indicate the interquartile range and whiskers the minimum–maximum values. No significant difference was detected between groups (Mann–Whitney U = 74, p = 0.200)

Effect of neuter status

When analyzing the entire cohort, neutered dogs (n = 9) demonstrated higher serum IGF-1 (median: 97.5 ng/mL) compared to intact dogs (n = 21; median: 51.8 ng/mL); however, this difference did not reach statistical significance (p = 0.094).

Within the alopecic group specifically, neutered dogs (n = 7, median IGF-1: 62.0 ng/mL) did not significantly differ from intact dogs (n = 4, median IGF-1: 31.7 ng/mL) (U = 9, p = 0.412).

No significant correlation was detected between serum IGF-1 concentration and age (Spearman’s ρ = 0.154, p = 0.412) or body weight (ρ = 0.089, p = 0.643) in the total population.

Serum biochemistry

Among the serum biochemical variables, serum alkaline phosphatase (ALP) activity was numerically higher in dogs with Alopecia X than in healthy controls (156 ± 108 U/L vs. 89 ± 34 U/L; P = 0.028). However, this difference did not remain statistically significant after Bonferroni correction for multiple comparisons (adjusted α = 0.003). No other serum biochemical parameter.

Discussion

This study provides the first breed-specific quantitative data regarding systemic IGF-1 status in Pomeranian dogs with Alopecia X. The principal finding—that serum IGF-1 concentrations do not differ significantly between affected and healthy Pomeranians—suggests that systemic IGF-1 deficiency is not a primary driver of AX in this breed. Our results contrast with classic descriptions of growth hormone-responsive dermatosis, where low IGF-1 was historically reported [7]. However, those studies often utilized heterogeneous breed populations and different assay techniques. The results of the present study support more recent evidence suggesting that most dogs with AX have normal growth hormone stimulation results [10], reinforcing the clinical consensus that AX is unlikely to represent a simple systemic hormonal deficiency state.

The significant overlap in IGF-1 ranges observed in our cohort (7–210 ng/mL) further indicates that isolated serum IGF-1 values cannot differentiate disease status. These findings align with the emerging paradigm of Alopecia X (AX) as a genetically programmed hair cycle arrest. This is notably supported by recent evidence from a cloned Pomeranian that developed identical AX lesions at the same age as its progenitor, independent of gonadal sex hormone exposure or environmental triggers [4].

While our data indicate that systemic IGF-1 values are non-discriminatory, the arrest of the hair cycle in AX may instead be driven by localized downregulation of key developmental pathways. Transcriptome profiling has revealed a significant downregulation of the Wnt and Sonic Hedgehog (Shh) pathways in the skin of affected Pomeranians [5]. Furthermore, our findings regarding normal systemic levels should be interpreted alongside recent immunohistochemical evidence showing a significant decrease in p63 immunoexpression within the follicles of affected dogs [6]. Because p63 is a master regulator of follicular stem cell maintenance and is functionally linked to Wnt/Shh signaling, its depletion suggests a “follicular-intrinsic” failure rather than a systemic endocrine one.

Our results show that future research should focus on intrafollicular IGF-1 signaling rather than systemic concentrations. Given the evidence of local stem cell compartment dysregulation [5, 6], future investigations should determine if local IGF-1 bioavailability is impaired at the follicular level despite the normal systemic concentrations observed in our results.

The significant imbalance in neuter status between our groups reflects the established epidemiological association between gonadectomy and AX. While the present study observed numerically higher IGF-1 in neutered dogs, the lack of statistical significance (likely due to Type II error given the small subgroup size) prevents definitive conclusions.

However, recent clinical evidence suggests that the hypothalamic-pituitary-gonadal (HPG) axis plays a more direct role in AX pathogenesis than previously recognized. For instance, successful hair regrowth has been reported in a neutered female Pomeranian using a deslorelin acetate (GnRH) implant after melatonin therapy had failed [12]. This observation supports the concept that modulation of the HPG axis can influence follicular cycling even in neutered dogs, although the underlying molecular mechanisms remain to be elucidated.

Furthermore, recent randomized clinical trials have tried to improve current therapeutic strategies for Alopecia X. A 2024 study comparing melatonin, photobiomodulation, and their combination in German Spitz dogs demonstrated that while melatonin remains a staple therapy, synergistic approaches may better address the underlying hair cycle arrest [13]. The mechanistic link between such therapies and the gonadal axis is further supported by a 2025 dose-response study of oral melatonin in intact male Pomeranians, which provided new insights into how melatonin modulates reproductive parameters with the follicular cycle [14].

Taken together, these data and recent therapeutic advances suggest, it remains unclear whether gonadectomy unmasks a latent follicular abnormality or directly alters the somatotropic axis. However, the efficacy of GnRH analogs and melatonin suggests that future research should focus on the cross-talk between the HPG and GH/IGF-1 axes at the level of the hair follicle.

Beyond the primary endocrine markers, the broader biochemical profile in this study remained largely within reference intervals, supporting the classification of AX as a non-systemic skin disorder.

Interestingly, serum ALP activity showed a nonsignificant tendency toward higher values in dogs with Alopecia X. Although the unadjusted comparison suggested a difference between groups, statistical significance was not retained after Bonferroni correction. Therefore, this observation should be interpreted cautiously. Nevertheless, because mild ALP elevations have been associated with glucocorticoid exposure and chronic physiological stress in dogs, future studies with larger cohorts should determine whether this finding represents a biologically meaningful feature of Alopecia X or simply reflects inter-individual variation.

Limitations

While our findings provide important baseline data, certain limitations warrant consideration. The most notable is the neuter status imbalance (63.6% in cases vs. 10.5% in controls; p = 0.002). As gonadectomy can modify the somatotropic axis, this represents a confounding factor that may influence the comparison of systemic IGF-1. Although we utilized secondary subgroup analyses, the lack of a primary ANCOVA to control for neuter status means the observed non-difference should be interpreted with this context in mind.

Additionally, we utilized a human competitive ELISA kit (LDN EIA-4147). While validated in-house with excellent cross-reactivity (98%) and recovery (92.5%), the absolute median values in our controls (~ 52 ng/mL) were lower than those typically reported using canine-specific assays [15]. This suggests a potential systematic underestimation of absolute concentrations, though it does not invalidate the relative comparison between our study groups.

The study is also characterized by a modest sample size; with 38% power to detect a medium effect size, we cannot entirely exclude the presence of subtle, biologically relevant differences. Furthermore, we measured total rather than free IGF-1. Since IGF-binding proteins (IGFBPs) dictate local bioactivity, our systemic results do not rule out localized signaling deficiencies at the follicle level. Finally, the cross-sectional nature of this work means we could not track IGF-1 fluctuations over the course of the disease or its treatment.

The lack of significant systemic IGF-1 differences in our cohort strongly suggests that the pathogenesis of AX may reside within the localized molecular environment of the hair follicle rather than in circulating hormone concentrations. IGF-1 is produced locally by the dermal papilla, acting in a paracrine fashion on the receptors of follicular epithelial cells to maintain the anagen phase. Therefore, localized signaling deficiencies or receptor down-regulation could trigger hair cycle arrest even when serum profiles are normal. This justifies a shift in focus toward the expression of these growth factors directly within the skin tissues.

Conclusions

In conclusion, serum IGF-1 concentrations did not differ significantly between Pomeranian dogs with Alopecia X and healthy controls in this study. The data argue against a systemic reduction in IGF-1 as a driver of AX in this population. Future research should prioritize investigating localized intra-follicular signaling pathways to further clarify the pathogenesis of this complex disorder.

Abbreviations

AX

Alopecia X

ELISA

Enzyme-linked immunosorbent assay

GH

Growth hormone

IGF-1

Insulin-like growth factor-1

IGFBP

Insulin-like growth factor binding protein

IQR

Interquartile range

Authors' contributions

ZH: Investigation, data curation, writing – original draft. AP: Methodology, validation, resources. JK: Conceptualization, formal analysis, writing – review & editing, supervision. All authors read and approved the final manuscript.

Funding

The study was supported by institutional resources of Ferdowsi University of Mashhad.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was approved by the Institutional Animal Care and Use Committee of Ferdowsi University of Mashhad (Permit Number: IR.UM.REC.1403.233). All owners provided written informed consent.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.