SPRY4-Related Hypogonadotropic Hypogonadism: Comprehensive Disease Report

Executive summary and evidence limitations

Hypogonadotropic hypogonadism 17 with or without anosmia (HH17; OMIM 615266) is the disease label applied to congenital or isolated gonadotropin-releasing hormone (GnRH) deficiency associated with heterozygous variants in SPRY4, which encodes the fibroblast-growth-factor signaling inhibitor Sprouty-4. Patients may have Kallmann syndrome—hypogonadotropic hypogonadism with anosmia/hyposmia—or normosmic disease. However, the SPRY4 evidence base remains small, many reported alleles are variants of uncertain significance (VUS), and oligogenic inheritance is common. Thus, “SPRY4-associated” is generally more defensible than assuming that every rare SPRY4 allele causes a fully penetrant monogenic disorder. The foundational study screened 386 unrelated CHH probands and 155 controls and found SPRY4 variants in 14 probands; individual FGF-network genes each explained only approximately 1–4% of that referral cohort. [Miraoui et al., published May 2, 2013; DOI/URL: https://doi.org/10.1016/j.ajhg.2013.04.008; PMID 23643382] (miraoui2013mutationsinfgf17 pages 1-2, miraoui2013mutationsinfgf17 pages 4-6)

No substantial SPRY4-specific clinical or mechanistic studies from 2023–2024 were found. Recent advances instead concern CHH genetic-panel interpretation, differential diagnosis, fertility management, and prediction of disease reversal. These general CHH findings are identified explicitly below and should not be treated as SPRY4-specific observations. (dwyer2024classesandpredictors pages 9-11, dwyer2024classesandpredictors pages 3-4, sayed2023paneltestingfor pages 2-3, panel2024diagnosisandtreatment pages 34-35)

Table: Evidence-grade summary of SPRY4-associated HH17, emphasizing variant uncertainty, oligogenic inheritance, the proposed FGF–MAPK mechanism, and limits of clinical and animal-model evidence.

1. Disease information

HH17 is a rare neurodevelopmental–endocrine disorder in which deficient GnRH secretion or action produces low sex-steroid concentrations with low or inappropriately normal LH and FSH. Complete anosmia with CHH is conventionally termed Kallmann syndrome; preserved smell defines normosmic CHH. Severe disease can present during neonatal “mini-puberty” with micropenis or cryptorchidism, whereas later presentations include absent/arrested puberty and infertility. A reported SPRY4 carrier instead underwent normal puberty and developed central hypogonadism at age 48, demonstrating that the associated phenotype need not be clinically congenital. (indirli2019ararespry4 pages 1-2, indirli2019ararespry4 pages 2-4, dwyer2024classesandpredictors pages 3-4)

Identifiers and terminology

• Disease: hypogonadotropic hypogonadism 17 with or without anosmia; HH17; SPRY4-related isolated/congenital hypogonadotropic hypogonadism; SPRY4-related Kallmann syndrome.
• OMIM: 615266.
• Gene/protein: SPRY4, Sprouty RTK signaling antagonist 4/Sprouty-4; OMIM 607984; chromosome 5q31.3. (miraoui2013mutationsinfgf17 pages 3-4, sayed2023paneltestingfor pages 2-3)
• MONDO: the requested mapping is MONDO:0014102, but it should be independently checked against the current MONDO release before database import. The available Open Targets lookup did not return an HH17–SPRY4 association and instead surfaced neighboring numbered HH entities, illustrating incomplete cross-resource harmonization. (OpenTargets Search: hypogonadotropic hypogonadism 17 with or without anosmia-SPRY4)
• Orphanet, MeSH, ICD-10 and ICD-11: no retrieved evidence established a dedicated SPRY4/HH17 code. Cases are ordinarily represented under broader congenital/isolated hypogonadotropic hypogonadism or Kallmann syndrome concepts; nonspecific endocrine codes should not be presented as exact HH17 identifiers.

The evidence is aggregated disease-level literature plus a very small number of individual published patients, not an EHR-derived population dataset. The adult-onset p.Arg53Gln report is explicitly a single patient. (indirli2019ararespry4 pages 1-2, miraoui2013mutationsinfgf17 pages 1-2)

2. Etiology, risk, protective, and environmental factors

The initiating factor is a germline SPRY4 sequence variant, usually heterozygous, that is hypothesized to alter negative regulation of FGF–FGFR signaling. For p.Ser241Tyr, experimental evidence indicates a gain of inhibitory function rather than SPRY4 loss of function. Other alleles have not been comparably validated. (stutz2021asprouty4mutation pages 1-2, stutz2021asprouty4mutation pages 9-10)

Genetic risk is likely context-dependent. SPRY4 variants have co-occurred with variants in FGFR1, DUSP6, TACR3, SEMA3A, PROKR2, and NSMF, supporting an oligogenic burden model. In the European-ancestry subset of the original FGF-network study, 24/124 variant-positive probands had variants in different genes—19%, 95% CI 12–26%—and 23/24 combinations included an FGF-network gene. This is strong evidence for CHH/FGF-network oligogenicity but not proof that every individual SPRY4 combination is pathogenic. (miraoui2013mutationsinfgf17 pages 12-14)

No validated SPRY4-specific environmental, infectious, toxic, occupational, dietary, lifestyle, epigenetic, or protective factor was identified. The adult-onset report proposed—without demonstrating—that modifying genes, intrauterine factors, or acquired environmental influences could affect penetrance. There are likewise no established gene–environment interactions, protective alleles, vaccines, or prophylactic drugs. (indirli2019ararespry4 pages 5-6)

3. Phenotypes

Reliable SPRY4-specific percentages cannot be calculated because carriers are few, variants differ, and several cases are oligogenic. Appropriate database frequency labels are therefore reported, variable, or unknown, not percentages extrapolated from CHH cohorts.

• Hypogonadotropic hypogonadism—laboratory/clinical phenotype; congenital, pubertal, or rarely adult-onset; severity variable. Suggested HPO: HP:0000044.
• Delayed, arrested, or absent puberty—clinical sign, generally apparent in adolescence and chronic without treatment. HPO: HP:0000823; absent secondary sexual characteristics: HP:0008187.
• Anosmia/hyposmia—congenital sensory sign in Kallmann presentations; typically stable. HPO: HP:0000458, HP:0004409. Normosmia is also documented. (indirli2019ararespry4 pages 2-4, gach2020newfindingsin pages 2-4)
• Olfactory-bulb/tract aplasia or hypoplasia—MRI sign. In the p.Arg53Gln patient, bulbs and tracts were absent and olfactory sulci hypoplastic, while hypothalamus, pituitary and stalk were normal. Suggested HPO: abnormality of the olfactory bulb HP:0002033. (indirli2019ararespry4 pages 1-2, indirli2019ararespry4 pages 2-4)
• Micropenis/underdeveloped male genitalia and cryptorchidism—neonatal or childhood markers of severe prenatal/mini-pubertal GnRH deficiency; not present in the adult-onset case, but underdeveloped genitalia occurred in the p.Lys177Arg case. HPO: HP:0000054, HP:0000028. (indirli2019ararespry4 pages 1-2, gach2020newfindingsin pages 2-4, dwyer2024classesandpredictors pages 3-4)
• Infertility, low libido, reduced erections/erectile dysfunction—adult reproductive symptoms. HPO: HP:0000789, decreased libido HP:0000158, erectile dysfunction HP:0000802. The p.Arg53Gln patient developed sexual symptoms at 48 years. (indirli2019ararespry4 pages 1-2, indirli2019ararespry4 pages 2-4)
• Low testosterone or estradiol with low/inappropriately normal LH and FSH—core biochemical abnormality. The adult-onset male had testosterone of 6.8 and 5.8 nmol/L on consecutive assessments. (indirli2019ararespry4 pages 1-2)
• Hearing loss and abnormal dentition were described among four earlier SPRY4-variant carriers, but neither frequency nor variant-specific causality is established. Suggested HPO: sensorineural hearing impairment HP:0000407 and hypodontia HP:0000668. (indirli2019ararespry4 pages 5-6)

Untreated pubertal delay, infertility, sexual dysfunction, and impaired body composition/bone health can substantially reduce psychosocial and physical quality of life, but no EQ-5D, SF-36, PROMIS, or SPRY4-specific quality-of-life dataset was identified. General CHH literature supports early treatment to improve sexual development, fertility potential, and psychological well-being. (vezzoli2023geneticarchitectureof pages 2-3)

4. Genetic and molecular information

SPRY4 is the only defining gene for HH17. The retrieved literature did not establish pathogenic SPRY4 deletions, duplications, translocations, repeat expansions, mitochondrial variants, or somatic disease alleles. Reported HH variants are germline heterozygous missense substitutions.

1. NM_030964.3:c.722C>A, p.(Ser241Tyr), rs139512218. This allele occurred in both Kallmann and normosmic CHH and alongside FGFR1, DUSP6, or TACR3 variants. In the original dataset, its MAF was 0.6% in controls and 0.5% in CHH—evidence against a highly penetrant monogenic pathogenic allele. It is reported as a ClinVar VUS and was maternally inherited in a later case. Nevertheless, cell assays indicate an FGF-selective inhibitory hypermorph. It should remain VUS/conflicting rather than being upgraded solely on functional evidence. (miraoui2013mutationsinfgf17 pages 12-14, gach2020newfindingsin pages 4-4)
2. c.530A>G, p.(Lys177Arg). Maternally inherited VUS in a male diagnosed with Kallmann syndrome at 13 years and underdeveloped genitalia; no direct functional validation. (gach2020newfindingsin pages 2-4, gach2020newfindingsin pages 5-5)
3. c.158G>A, p.(Arg53Gln). Rare heterozygous allele, reported MAF <0.01, found as the sole result on a 28-locus panel in one man with congenital severe hyposmia and adult-onset HH. No family segregation or functional test was reported; candidate/VUS-level evidence is appropriate. (indirli2019ararespry4 pages 1-2, indirli2019ararespry4 pages 2-4)

No validated SPRY4 modifier gene, disease-specific DNA methylation signature, histone alteration, or chromatin defect is known. The co-occurring genes listed above are better treated as potential oligogenic partners than proven modifiers.

5. Environmental information

No SPRY4-specific association with smoking, alcohol, diet, exercise, endocrine disruptors, pollution, radiation, medications, occupational agents, or infection has been demonstrated. Acquired functional hypogonadotropic hypogonadism caused by undernutrition, excessive exercise, severe illness, medication, or pituitary disease belongs in the differential diagnosis, not in HH17 etiology. No pathogen or zoonotic mechanism applies. (panel2024diagnosisandtreatment pages 34-35)

6. Mechanism and pathophysiology

Ordered causal chain

1. A function-altering germline SPRY4 allele—demonstrated for p.Ser241Tyr as increased inhibitory activity—leads to excessive restraint of FGF-responsive signaling. (stutz2021asprouty4mutation pages 1-2, stutz2021asprouty4mutation pages 9-10)
2. Excess SPRY4 inhibition leads to reduced FGFR-driven RAS–RAF–MEK–ERK/MAPK output; p.Ser241Tyr inhibited FGF- but not EGF-induced signaling in vitro. (stutz2021asprouty4mutation pages 1-2, stutz2021asprouty4mutation pages 9-10)
3. Reduced FGF/MAPK signaling is inferred to lead to impaired olfactory-placode patterning, olfactory axon/ensheathing-cell development, and/or GnRH-neuron specification, survival, or migration. These neuronal consequences have not been demonstrated directly in SPRY4-mutant human GnRH cells. (miraoui2013mutationsinfgf17 pages 3-4, cho2019nasalplacodedevelopment pages 19-20)
4. Branch A: impaired olfactory development leads to hypoplastic/absent olfactory bulbs and anosmia/hyposmia (Kallmann phenotype). Branch B: deficient hypothalamic GnRH neuronal number/function leads to reduced pulsatile GnRH drive. (indirli2019ararespry4 pages 1-2, indirli2019ararespry4 pages 2-4)
5. Reduced GnRH drive results in low or inappropriately normal LH/FSH, which leads to reduced gonadal sex-steroid synthesis and impaired gametogenesis. (dwyer2024classesandpredictors pages 3-4, panel2024diagnosisandtreatment pages 34-35)
6. Sex-steroid and gametogenic failure results in absent/arrested puberty, undervirilization or amenorrhea, sexual dysfunction, and infertility. (dwyer2024classesandpredictors pages 3-4)

Sprouty proteins are intracellular antagonists of receptor-tyrosine-kinase signaling, with strongest evidence for modulation of FGF-induced MAPK/ERK; occasional PI3K and phospholipase-C effects are described, but no HH17-specific metabolic, immune, inflammatory, apoptotic, autophagic, fibrotic, or oxidative-stress mechanism is established. (stutz2021asprouty4mutation pages 1-2)

In WI-38 human embryonic fibroblasts, p.Ser241Tyr reduced migration to 9.106 ± 0.305 μm/h, compared with 11.77 ± 0.685 μm/h for wild-type SPRY4 and 12.36 ± 0.781 μm/h for control, and prolonged approximate doubling time from 10 to 15 days. These assays support altered migration/proliferation but used lung fibroblasts and U2OS osteosarcoma cells—not olfactory or GnRH neurons. The authors’ abstract states directly: “the described Spry4 mutation creates a hyperactive version of a selective inhibitory molecule and can thereby contribute to a weakened FGF signaling.” [Stütz et al., published February 21, 2021; https://doi.org/10.3390/ijms22042145] (stutz2021asprouty4mutation pages 1-2, stutz2021asprouty4mutation pages 4-7)

Suggested ontology annotations include FGF receptor signaling pathway (GO:0008543), MAPK cascade (GO:0000165), negative regulation of ERK1/ERK2 cascade (GO:0070373), neuron migration (GO:0001764), olfactory bulb development (GO:0021772), and regulation of gonadotropin secretion (GO:0032276). Relevant cells are GnRH neurons, olfactory sensory neurons, olfactory ensheathing glia, pituitary gonadotrophs, Leydig cells, Sertoli cells, ovarian granulosa cells, and theca cells; exact CL identifiers should be checked in the target ontology release.

Available expression analysis is indirect: SPRY4 expression was higher in cultured olfactory ensheathing cells than in olfactory sensory neurons or adult mouse GnRH-neuron datasets. No HH17 patient single-cell, spatial-transcriptomic, proteomic, metabolomic, lipidomic, multi-omic, or CRISPR-screen dataset was found. (cho2019nasalplacodedevelopment pages 19-20)

7. Anatomical structures affected

The primary system is the hypothalamic–pituitary–gonadal axis. Direct or developmental sites include nasal/olfactory placode, olfactory epithelium and axonal scaffold, olfactory bulbs/tracts, preoptic–hypothalamic GnRH neuronal network, pituitary gonadotrophs functionally downstream, and testes or ovaries secondarily deprived of gonadotropin stimulation. (indirli2019ararespry4 pages 2-4, miraoui2013mutationsinfgf17 pages 3-4, dwyer2024classesandpredictors pages 3-4)

Suggested UBERON concepts are olfactory epithelium, olfactory bulb (UBERON:0002264), olfactory tract, hypothalamus (UBERON:0001898), pituitary gland (UBERON:0000007), testis (UBERON:0000473), and ovary (UBERON:0000992). Relevant subcellular locations include cytosol, plasma-membrane-associated RTK signaling complexes, and ERK-containing signaling compartments; suitable GO cellular-component terms include cytoplasm (GO:0005737) and plasma membrane (GO:0005886). Olfactory involvement is generally bilateral; no consistent lateralization is reported.

8. Temporal development and course

The initiating developmental susceptibility is prenatal, when olfactory and GnRH systems form, but clinical recognition varies:

• neonatal/infantile: micropenis or cryptorchidism from deficient prenatal/mini-pubertal HPG activation;
• adolescence: absent or arrested puberty, small testes, or primary amenorrhea;
• adulthood: infertility or sexual dysfunction;
• exceptional SPRY4 report: congenital hyposmia with normal puberty and HH emerging at 48 years. (indirli2019ararespry4 pages 1-2, indirli2019ararespry4 pages 2-4, dwyer2024classesandpredictors pages 3-4)

The condition is generally chronic but variable. General CHH—not SPRY4-specific—reverses in approximately 10–15% of cases after sex-steroid, gonadotropin, or pulsatile-GnRH treatment. In a 2024 six-center study, reversal occurred at mean age 27.4 years, and oligogenicity was less common among reversals than non-reversals (29.3% versus 58.9%). Relapse can occur, so recovery requires continued surveillance. No SPRY4-specific reversal rate is available. [Dwyer et al., published April 2024; https://doi.org/10.1016/S2213-8587(24)00028-7] (dwyer2024classesandpredictors pages 9-11, dwyer2024classesandpredictors pages 3-4)

Critical intervention windows include mini-puberty/early infancy in severely affected boys, timely adolescent pubertal induction for bone and psychosocial health, and fertility-directed gonadotropin treatment before prolonged unopposed testosterone exposure where feasible.

9. Inheritance and population

Reported SPRY4 alleles are heterozygous and the disease label is commonly treated as autosomal dominant. Nevertheless, maternal transmission to an affected male, occurrence in controls, variable olfactory/reproductive phenotypes, and frequent second-gene variants indicate incomplete penetrance, variable expressivity, and possible oligogenic inheritance. No anticipation, germline mosaicism, founder effect, consanguinity association, or reliable carrier frequency has been established. (miraoui2013mutationsinfgf17 pages 12-14, gach2020newfindingsin pages 5-5, gach2020newfindingsin pages 4-4)

HH17-specific incidence, prevalence, sex ratio, age distribution, ancestry enrichment, and geographic distribution are unknown. Detection of SPRY4 variants in 14/386 discovery probands and 2/47 Polish patients are referral-cohort variant yields—not population prevalence estimates. General CHH is approximately fourfold more frequently diagnosed in males, but ascertainment and subtler female phenotypes contribute to this imbalance. (miraoui2013mutationsinfgf17 pages 1-2, dwyer2024classesandpredictors pages 3-4, gach2020newfindingsin pages 2-4)

10. Diagnostics

Clinical and laboratory evaluation

Diagnosis requires compatible reproductive development plus low testosterone/estradiol with low or inappropriately normal LH and FSH, after excluding identifiable hypothalamic–pituitary or systemic causes. The 2024 reversal study operationalized male CHH as absent/incomplete puberty by 18 years, testosterone <6 nmol/L, low/inappropriately normal gonadotropins, and no acquired hypothalamic/pituitary cause; testes <4 mL defined absent puberty. (dwyer2024classesandpredictors pages 3-4)

Recommended evaluation includes detailed neonatal and pubertal history; Tanner stage and testicular volume; micropenis/cryptorchidism; menstruation and secondary sexual characteristics; formal or validated smell assessment; LH, FSH and sex steroids; prolactin, thyroid and other pituitary hormones; iron studies and systemic evaluation as indicated; semen analysis in adult men; pelvic ultrasound in females when appropriate; bone age and bone-density assessment; and MRI of pituitary/hypothalamus and olfactory structures when clinically indicated. GnRH stimulation, overnight LH pulsatility, inhibin B, AMH, INSL3, and hCG-stimulated testosterone can support assessment but are not individually definitive in distinguishing CHH from self-limited delayed puberty. (indirli2019ararespry4 pages 2-4, vezzoli2023geneticarchitectureof pages 2-3)

Genetic testing

A contemporary multigene CHH/Kallmann panel is preferable to SPRY4-only sequencing because more than 60 genes may contribute and oligogenic findings are common. Panel-based studies identify a potentially relevant variant in approximately 21–51% of CHH/KS patients. SPRY4 is a less frequently identified gene and should be interpreted under ACMG/AMP criteria with phenotype concordance, ancestry-matched population frequency, segregation, functional evidence, and second-gene burden. Exome or genome sequencing is appropriate after a nondiagnostic panel or when syndromic/structural disease is suspected; RNA sequencing remains investigational. CMA is reasonable for congenital anomalies or neurodevelopmental features; routine karyotype, FISH, mitochondrial, or repeat-expansion testing is not indicated specifically for HH17. [Al Sayed & Howard, published 2023; https://doi.org/10.1038/s41431-022-01261-0] (sayed2023paneltestingfor pages 2-3)

Differential diagnosis

Exclude self-limited delayed puberty; functional hypothalamic amenorrhea from undernutrition/exercise/stress; chronic systemic disease; hyperprolactinemia; pituitary/suprasellar tumors; hemochromatosis, sarcoidosis, tuberculosis or histiocytosis; head trauma or pituitary apoplexy; exogenous androgens, opioids and other suppressive drugs; and syndromic/genetic CHH involving ANOS1, FGFR1/FGF8, CHD7, PROK2/PROKR2, GNRHR, KISS1R, TAC3/TACR3, SOX10 and others. The 2023 delayed-puberty study found classical HH-associated features in 38.5% of HH versus 15.4% of self-limited delayed puberty, but biochemical overlap remained substantial. (vezzoli2023geneticarchitectureof pages 2-3, panel2024diagnosisandtreatment pages 34-35)

Population newborn screening is unavailable. Targeted cascade testing and longitudinal follow-up are reasonable in relatives once a genuinely pathogenic familial variant is established. In isolated congenital anosmia, genetic evaluation may identify individuals requiring reproductive follow-up because the p.Arg53Gln case developed HH decades later. (indirli2019ararespry4 pages 1-2)

11. Outcome and prognosis

HH17 is not known to shorten life expectancy, and no disease-specific mortality or survival statistic exists. Principal morbidity is absent/incomplete sexual development, infertility, sexual dysfunction, reduced bone mass if sex-steroid deficiency is prolonged, and psychosocial burden. Smell loss is usually persistent, while endocrine manifestations are treatable. Testosterone normalized levels and improved sexual symptoms in the adult-onset SPRY4 case. (indirli2019ararespry4 pages 2-4)

General CHH fertility is often recoverable: approximately 75% of affected males can achieve spermatogenesis/fertility with FSH plus hCG or pulsatile GnRH, although outcomes are poorer with cryptorchidism and very small pretreatment testes. Approximately 10–15% undergo endocrine reversal; larger baseline testes predict reversal, whereas cryptorchidism and oligogenicity are unfavorable markers. These figures cannot be assumed to represent HH17 specifically. (dwyer2024classesandpredictors pages 9-11, dwyer2024classesandpredictors pages 3-4)

12. Treatment and current implementation

No approved SPRY4-directed, gene, cell, RNA, CRISPR, immunologic, or pathway-targeted therapy exists. Treatment follows CHH phenotype and reproductive goals.

• Puberty/maintenance: gradually titrated testosterone in males; estradiol followed by cyclic progestogen in females with a uterus. Suggested NCIT concepts: Testosterone (NCIT:C862), Estradiol (NCIT:C483), hormone replacement therapy.
• Male fertility: hCG to stimulate Leydig-cell testosterone, adding FSH after testosterone normalization; the 2024 AUA/ASRM guideline gives hCG 500–2,500 IU two to three times weekly, with response related to pretreatment testicular size. Pulsatile GnRH is an alternative where available. Exogenous testosterone should not be used when current or future fertility is desired because it suppresses intratesticular testosterone and spermatogenesis. [AUA/ASRM guideline, amended 2024] (panel2024diagnosisandtreatment pages 34-35)
• Female fertility: pulsatile GnRH for hypothalamic deficiency or individualized gonadotropin ovulation induction. A 2023 CHH case achieved twin delivery after personalized hMG plus recombinant LH, illustrating real-world feasibility but not SPRY4-specific efficacy.
• Supportive care: bone-health monitoring, adequate calcium/vitamin D and weight-bearing activity, sexual and psychological support, fertility counseling, cryptorchidism management, and hearing/dental assessment when indicated.

Retrieved ClinicalTrials.gov examples were general HH/IHH rather than SPRY4-genotype trials: NCT00064987 (FSH/testicular development; terminated; n=19), NCT02880280 (hMG+hCG; phase 4; n=40), NCT01403532 (sequential therapy; completed phase 4; n=100), and NCT03687606 (hCG versus hCG+hMG; phase 4; n=210). These investigate endocrine replacement/fertility induction, not molecular correction of SPRY4 signaling.

No SPRY4 pharmacogenomic association or genotype-guided dose recommendation is established. Suggested NCIT intervention terms include gonadotropin therapy, human chorionic gonadotropin, follicle-stimulating hormone, gonadotropin-releasing hormone, testosterone replacement therapy, estrogen replacement therapy, and ovulation induction.

13. Prevention

Primary prevention of a de novo or inherited developmental allele through lifestyle change is not possible. No vaccine, environmental avoidance program, or prophylactic medication applies. Secondary prevention consists of early recognition in infants with micropenis/cryptorchidism, adolescents with pubertal delay, adults with infertility, and individuals with congenital anosmia; prompt hormonal treatment helps prevent impaired bone accrual, psychosocial consequences, and delayed fertility care. Tertiary prevention includes sustained sex-steroid replacement, bone surveillance, fertility-preserving treatment, and management of cryptorchidism and associated sensory/dental abnormalities. (vezzoli2023geneticarchitectureof pages 2-3, dwyer2024classesandpredictors pages 3-4)

Genetic counseling should emphasize uncertain penetrance, variable expressivity, possible oligogenicity, and the danger of using a VUS for irreversible reproductive decisions. Cascade, prenatal, or preimplantation testing is appropriate only after expert confirmation of a pathogenic/likely pathogenic familial allele and a defensible inheritance model.

14. Other species and natural disease

No naturally occurring SPRY4-associated hypogonadotropic-hypogonadism syndrome was identified in companion animals, livestock, or wildlife; no breed/VBO association or veterinary prevalence is established. The disorder is noninfectious and nonzoonotic. Orthologous Spry4 is evolutionarily conserved in vertebrates, supporting comparative FGF-signaling studies, but conservation alone does not establish animal disease.

15. Model organisms and experimental systems

Mouse (Mus musculus; NCBI Taxon 10090): Spry4-null mice are viable and fertile, although a subset dies shortly after birth with mandibular defects; growth retardation and polysyndactyly occur. Their embryonic fibroblasts show increased FGF-induced ERK activation, and combined Spry2/Spry4 deletion is embryonic lethal. This knockout models loss of FGF restraint—the opposite direction from inhibitory-hypermorph p.Ser241Tyr—and does not convincingly reproduce human HH17. Olfactory and GnRH-neuron phenotypes were not sufficiently characterized in the retrieved evidence. (stutz2021asprouty4mutation pages 1-2)

Human cellular models: adenoviral wild-type and p.Ser241Tyr SPRY4 were studied in WI-38 embryonic lung fibroblasts and U2OS osteosarcoma cells. These systems demonstrate FGF-selective MAPK inhibition and reduced migration/proliferation but lack disease-relevant GnRH neurons, olfactory sensory neurons, or olfactory ensheathing cells. (stutz2021asprouty4mutation pages 1-2, stutz2021asprouty4mutation pages 4-7, stutz2021asprouty4mutation pages 9-10)

Future high-value models: patient-derived iPSCs differentiated into GnRH neurons and olfactory lineages; isogenic CRISPR-corrected controls; knock-in p.Ser241Tyr mice or organoids; and single-cell/spatial profiling of olfactory–GnRH development. Human stem-cell-derived GnRH neurons can exhibit approximately 60-minute pulsatile GnRH release and respond to FGF8/kisspeptin, providing a feasible platform, although no SPRY4 HH17 line was identified.

Overall interpretation

The most defensible current model is that rare SPRY4 variants can contribute to the CHH/Kallmann spectrum by perturbing FGF–MAPK signaling, frequently in an incompletely penetrant or oligogenic context. p.Ser241Tyr has strong biochemical evidence for an inhibitory hypermorph but problematic case–control frequency and VUS classification; p.Lys177Arg and p.Arg53Gln have only limited patient-level evidence. Accordingly, an HH17 knowledge-base entry should preserve the OMIM disease concept while marking variant pathogenicity, penetrance, disease-specific epidemiology, and most genotype–phenotype frequencies as unresolved. Recent 2023–2024 work strengthens multigene testing and individualized CHH management, but it does not yet validate a SPRY4-specific diagnostic criterion or therapy. (dwyer2024classesandpredictors pages 9-11, miraoui2013mutationsinfgf17 pages 12-14, stutz2021asprouty4mutation pages 9-10, sayed2023paneltestingfor pages 2-3)

References

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