rs121434293 — SLC39A4 SLC39A4 Gln278His

ZIP4 Gln278His — The Intestinal Zinc Gate and Acrodermatitis Enteropathica

The body cannot make zinc — every microgram enters through the gut, and the ZIP4 transporter (SLC39A4)¹¹ ZIP4 transporter (SLC39A4)
ZIP4 is a member of the Zrt/Irt-like protein (ZIP/SLC39) family. It is the primary high-affinity zinc uptake transporter expressed on the apical surface of enterocytes in the duodenum and proximal jejunum — the sites of maximal dietary zinc absorption. is the molecular gate that makes that absorption possible. When both copies of SLC39A4 carry loss-of-function mutations, the gate fails, and zinc deficiency becomes severe enough to cause acrodermatitis enteropathica (AE)²² acrodermatitis enteropathica (AE)
AE (OMIM #201100) is the inherited form of severe zinc deficiency. It typically presents in infancy with a characteristic triad: periorificial and acral dermatitis, alopecia, and diarrhea. Without treatment it is fatal; with lifelong zinc supplementation, prognosis is excellent..

rs121434293 encodes the Gln278His substitution (c.834G>C, NM_017767.3) — a glutamine-to-histidine change in the transmembrane domain of ZIP4. It was classified as pathogenic by ClinVar (variation ID 18584, RCV000003723) based on OMIM curation and functional data. Heterozygous carriers have one functioning copy of ZIP4 and do not develop AE but may warrant attention in contexts of low dietary zinc intake or increased zinc demand.

The Mechanism

ZIP4 is an 8-transmembrane-domain protein expressed on the enterocyte apical membrane that actively transports luminal zinc into the cell. The protein is dynamically regulated: during zinc deficiency, ZIP4 mRNA is stabilised and surface expression increases; during zinc sufficiency, the protein is ubiquitinated and degraded, preventing toxic zinc accumulation. ³³ Küry et al. showed that AE-associated missense mutations reduce zinc uptake activity, disrupt zinc-responsive trafficking to the plasma membrane, and impair proteolytic processing of the extracellular amino-terminal domain — three distinct functional mechanisms all converging on the same phenotype.

The Gln278 residue sits within a transmembrane segment. Substitution to histidine introduces a bulkier, positively charged imidazole side chain that alters the three-dimensional conformation of the transport pore. Functional studies of analogous AE mutations demonstrate that even single amino acid changes in transmembrane residues can abolish zinc transport activity or prevent the protein from reaching the plasma membrane in a zinc-responsive manner.

The Evidence

SLC39A4 was identified as the AE gene⁴⁴ SLC39A4 was identified as the AE gene
Kury et al. Identification of SLC39A4, a gene involved in acrodermatitis enteropathica. Nature Genetics, 2002 by mutation analysis in eight affected families. All patients were either homozygous or compound heterozygous for loss-of-function variants. Since then, the mutation spectrum has expanded substantially — by the time of the 2009 mutation update⁵⁵ 2009 mutation update
Wang et al. An update on mutations of the SLC39A4 gene in acrodermatitis enteropathica. Dermatology, 2009, over 40 pathogenic variants had been catalogued across all 12 exons.

The rs121434293 G allele (Gln278His) appears in ClinVar as pathogenic, submitted by OMIM-curated records. Its population frequency is extremely rare — just one occurrence in 77,444 chromosomes from the Japanese 38KJPN cohort (G allele frequency ~0.00001). No homozygous GG individuals have been observed in population databases, consistent with the clinical severity of homozygous AE.

Treatment outcomes are excellent when zinc is replaced⁶⁶ Treatment outcomes are excellent when zinc is replaced
Alwadany et al. Acrodermatitis enteropathica: A rare case with lifelong implications. Cureus, 2023. Clinical response to high-dose oral zinc sulfate typically appears within 5–10 days. Skin lesions resolve within weeks, and with lifelong supplementation the prognosis is essentially normal.

Practical Actions

For homozygous carriers (disease state): this is a medical condition requiring immediate specialist referral, lifelong oral zinc replacement, and regular monitoring of serum zinc, copper, and alkaline phosphatase. Elemental zinc dosing starts at 3–10 mg/kg/day and is adjusted to maintenance (1–3 mg/kg/day) once zinc levels normalise. Zinc sulfate is the most widely studied formulation; zinc gluconate or acetate may be used when gastrointestinal side effects occur.

For heterozygous carriers: zinc absorption capacity is reduced on one allele. Dietary zinc intake from red meat, shellfish (especially oysters), legumes, nuts, and seeds is important, and supplementation should be considered during periods of increased demand (growth, pregnancy, illness).

Interactions

AE requires biallelic loss of function — two mutant SLC39A4 alleles are needed for disease. rs121434293 (Gln278His) can combine with any other pathogenic SLC39A4 variant (compound heterozygosity) to produce full AE. Carriers of this variant who have a partner who is also a carrier of any pathogenic SLC39A4 variant face a 25% per-pregnancy risk of an affected child — genetic counselling is indicated. Dietary zinc insufficiency (common with vegan diets or low-animal-protein diets) can lower the functional reserve in heterozygous carriers and transiently worsen zinc status.