rs121434287 — SLC39A4 SLC39A4 zinc transporter variant

Pathogenic missense variant in the intestinal zinc transporter ZIP4, causing acrodermatitis enteropathica — a rare autosomal recessive disorder of severe zinc deficiency — when inherited in biallelic form

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ZIP4 Pro200Leu — A Founding Mutation in Acrodermatitis Enteropathica

Every cell in your body needs zinc, yet humans have no meaningful way to store it. Every milligram must be absorbed fresh from the diet, almost entirely through the duodenum and proximal jejunum. The protein responsible for ferrying zinc from the gut lumen into intestinal cells is ZIP411 ZIP4
Zinc/Iron Regulated Transporter-related Protein 4 — encoded by SLC39A4 (solute carrier family 39 member 4) on chromosome 8q24.3, a twelve-pass transmembrane transporter that acts as the body's primary zinc gate. When ZIP4 is broken, zinc cannot cross the intestinal wall in sufficient quantities, and the consequences unfold quickly.

The c.599C>T variant (rs121434287) swaps a proline for a leucine at position 200 of the ZIP4 protein (p.Pro200Leu). It is one of the founding mutations identified in acrodermatitis enteropathica22 acrodermatitis enteropathica
AE — from Greek: acral (affecting the extremities and face), dermatitis (skin inflammation), and enteropathica (intestinal disease). First described by Brandt in 1936 and named by Danbolt and Closs in 1943 (AE), a rare autosomal recessive disorder of inherited zinc deficiency. Two copies of pathogenic SLC39A4 variants — either homozygous or compound heterozygous — lead to near-complete failure of intestinal zinc absorption, producing the clinical triad of periorificial and acral dermatitis, chronic diarrhea, and alopecia.

The Mechanism

ZIP4 is an unusual transporter: it moves zinc by coupling zinc influx to proton influx, exploiting the pH gradient at the gut lumen surface. The protein folds into an extracellular domain (ECD) containing two subdomains — the HRD domain and the PCD domain33 PCD domain
Potentially Conserved Domain — a structural region conserved across ZIP family members — linked by a short linker region that includes Pro200.

Structural studies44 Structural studies
Kuliyev E et al. Zinc transporter mutations linked to acrodermatitis enteropathica disrupt function and cause mistrafficking. J Biol Chem, 2021 showed that Pro200 sits in this linker region and that the P200L substitution causes ZIP4 to misfold. The mutant protein fails to traffic to the apical cell surface of enterocytes, becoming trapped in the endoplasmic reticulum with immature glycosylation. The functional result is complete abolition of zinc transport activity — not just a partial reduction. Cells expressing P200L ZIP4 take up zinc at rates indistinguishable from cells expressing no ZIP4 at all.

Functional studies55 Functional studies
Hoch E et al. Elucidating the H+ Coupled Zn2+ Transport Mechanism of ZIP4; Implications in Acrodermatitis Enteropathica. Int J Mol Sci, 2020 confirmed that P200L disrupts the proton-coupled zinc transport mechanism specifically, with the mutant showing severely reduced capacity to couple H+ influx to Zn2+ uptake compared to wild-type ZIP4.

The Evidence

Acrodermatitis enteropathica is one of the better-characterized single-gene zinc disorders precisely because its cause was confirmed at the molecular level. SLC39A4 was identified as the AE gene in 2002, and the Pro200Leu variant is among the earliest mutations reported. A comprehensive mutation update66 comprehensive mutation update
Schmitt S et al. An update on mutations of the SLC39A4 gene in acrodermatitis enteropathica. Hum Mutat, 2009 catalogued 44 distinct pathogenic variants, documenting the mutational spectrum across all exons and confirming that most patients carry compound heterozygous mutations rather than two copies of the same variant.

ClinVar lists this variant (VCV000003537) as Pathogenic/Likely pathogenic with criteria provided by seven independent diagnostic laboratories, with no classification conflicts. The associated condition is hereditary acrodermatitis enteropathica (OMIM 201100).

Without zinc replacement, AE follows a predictable course: infants present within weeks of weaning with periorificial dermatitis, diarrhea, failure to thrive, and alopecia. The condition can be fatal if unrecognized. With consistent zinc supplementation (5–10 mg/kg/day elemental zinc for acute disease; 1–2 mg/kg/day for maintenance), symptoms resolve rapidly and prognosis is excellent — lifelong supplementation is required, but patients can live normally.

Heterozygous Carriers

Heterozygous carriers have one functional ZIP4 allele and one P200L allele. With 50% of ZIP4 protein functioning normally, zinc absorption is maintained at sufficient levels for health under normal dietary conditions. Published case series confirm that parents of AE patients — who are obligate heterozygotes — do not develop AE. Some studies have noted that carriers may have modestly reduced zinc absorption under high-demand conditions (illness, pregnancy, poor diet), but this has not been quantified precisely and clinical AE does not occur in heterozygotes.

Practical Actions

Because AE is autosomal recessive, the practical significance of a single heterozygous P200L allele is primarily in the context of family planning and reproductive genetics. Carriers should be aware that if both parents carry a pathogenic SLC39A4 variant, each child has a 25% chance of inheriting biallelic variants and developing AE. Prenatal or preconception genetic counseling is appropriate when a carrier couple is identified.

For homozygous or compound heterozygous individuals, the clinical course depends on early identification and zinc supplementation initiation. Modern diagnostic genetic testing can confirm the diagnosis, and treatment (zinc sulfate orally) is inexpensive, highly effective, and well tolerated.

Interactions

Compound heterozygosity is the rule rather than the exception in AE. Most patients carry two different pathogenic SLC39A4 variants on their two chromosomes — for example, P200L on one chromosome and a frameshift or splice-site mutation on the other. The clinical severity is generally comparable across different compound heterozygous combinations, though some genotype-phenotype variability exists. For AE patients, the supervising clinician should characterize both SLC39A4 alleles to confirm the diagnosis and facilitate family cascade testing.

Drug Interactions

ciprofloxacin reduced_efficacy literature
doxycycline reduced_efficacy literature
risedronate reduced_efficacy literature

Nutrient Interactions

zinc reduced_absorption
copper altered_metabolism

Genotype Interpretations

What each possible genotype means for this variant.

GG Non-Carrier Normal

Normal ZIP4 function — typical zinc absorption

With no copies of the Pro200Leu variant, your SLC39A4 gene produces fully functional ZIP4 transporter. Zinc is absorbed normally through the duodenum and proximal jejunum. You do not carry a pathogenic allele that could be transmitted to offspring — your children can only inherit a P200L allele if your partner also carries one.

Standard dietary zinc intake (8 mg/day for women, 11 mg/day for men) is sufficient for your genetic profile.

AA Homozygous Deficient

Homozygous Pro200Leu — severe zinc malabsorption; consistent with acrodermatitis enteropathica

With two copies of Pro200Leu, neither of your ZIP4 proteins can traffic to the enterocyte surface or transport zinc. Laboratory studies confirmed that the P200L variant causes complete loss of zinc uptake activity and intracellular protein mistrafficking (Kuliyev et al., J Biol Chem 2021). Plasma zinc is severely reduced; alkaline phosphatase — a zinc-dependent enzyme — is correspondingly low.

Acrodermatitis enteropathica classically presents in formula-fed infants within weeks of birth, or in breastfed infants at weaning, because human breast milk contains a zinc ligand (not present in formula) that enables some zinc absorption even without functional ZIP4. In breastfed infants, the onset of symptoms is therefore delayed until weaning, when this alternative absorption route is lost.

Oral zinc supplementation (zinc sulfate, gluconate, or acetate) is the standard treatment. Initial dosing for acute disease is 5–10 mg/kg/day elemental zinc; maintenance dosing (lifelong) is 1–2 mg/kg/day. Clinical response is rapid: skin lesions begin resolving within days and alopecia reverses within weeks. Patients require lifelong supplementation because the genetic defect in ZIP4 cannot be corrected — once supplementation is stopped, deficiency recurs.

Monitoring zinc levels every 3–6 months ensures supplementation adequacy. Occasional measurement of serum copper is also advisable because high-dose zinc supplementation can impair copper absorption through competitive inhibition.

AG Carrier Carrier

Heterozygous carrier of Pro200Leu — single-allele status, no clinical zinc deficiency

One functional ZIP4 allele is sufficient to support adequate zinc absorption under normal dietary conditions. Parents of confirmed acrodermatitis enteropathica patients — who are obligate P200L heterozygotes or carry another pathogenic SLC39A4 variant — do not develop the condition themselves. Clinical zinc deficiency is not expected from single-allele carrier status.

The primary significance of heterozygous carrier status is reproductive: if both parents carry a pathogenic SLC39A4 variant, each pregnancy has a 25% chance of producing a child with biallelic variants and AE. Genetic counseling is appropriate for carrier couples planning a family.

Under physiological stress (illness, pregnancy, extremely low dietary zinc), carriers might theoretically be at slightly higher risk for marginal zinc insufficiency due to one lower-activity allele, but this has not been confirmed in clinical studies and does not rise to the level of clinical relevance without additional risk factors.