Renal Hypomagnesemia 4 — comprehensive disease-characteristics report

Disease: Renal hypomagnesemia 4
Preferred molecular designation: EGF-related primary renal hypomagnesemia with intellectual disability
MONDO: MONDO:0012717
Disease class: Mendelian renal tubular magnesium-transport disorder
Evidence status: Exceptionally rare; the molecularly confirmed human evidence remains limited to two affected sisters from one consanguineous Dutch family. Consequently, apparent phenotype frequencies of 100% are not reliable population estimates. OMIM itself marks the phenotype with a question mark, reflecting the limited genetic evidence. [392]

1. Disease information

1.1 Definition and overview

Renal hypomagnesemia 4 (HOMG4) is an autosomal-recessive disorder in which defective basolateral targeting of pro-epidermal growth factor impairs EGF–EGFR stimulation of the apical magnesium channel TRPM6 in distal convoluted tubule cells. The resulting failure of renal magnesium conservation causes chronic hypomagnesemia, infantile generalized seizures, developmental delay, and moderate intellectual disability, while serum calcium and urinary calcium are characteristically normal. [113][391]

The landmark molecular study identified homozygous EGF c.3209C>T, p.(Pro1070Leu) in the two sisters. Its abstract summarized the core mechanism as: “The mutation leads to impaired basolateral sorting of pro-EGF.” It further linked inadequate renal EGFR stimulation to insufficient TRPM6 activation and magnesium loss. Human clinical, cell-biological, electrophysiologic, and pharmacologic evidence were included in that report. PMID: 17671655; DOI: 10.1172/JCI31680; published August 1, 2007. [113]

1.2 Identifiers and nomenclature

The current Orphanet entry gives infancy/childhood onset, absence of secondary hypocalcemia and obesity, and prevalence below one per million. [134] The DO definition and historical ontology cross-references include OMIM 611718, ICD-10-CM E83.4, and ORDO:34527. [391]

1.3 Synonyms

These synonyms are consolidated in MONDO-linked resources and the current/historical Orphanet nomenclature. [394]

1.4 Data provenance

The disease entry is based on:

• Individual-level human observations: two sisters, originally reported clinically in 1987 and molecularly investigated in 2007.
• Family segregation: affected sisters, parents, unaffected siblings, and extended relatives.
• Aggregate resources: OMIM, MONDO, Orphanet, ClinVar, Disease Ontology, UniProt.
• Experimental evidence: HEK293 and polarized MDCK cells, rat-kidney immunohistochemistry, and a clinical pharmacologic analogue involving cetuximab-treated patients.

It is not based on an EHR cohort, population registry, randomized trial, or broad natural-history series.

2. Etiology

2.1 Primary causal factor

The established initiating lesion is homozygosity for the germline missense variant:

NM_001963.6(EGF):c.3209C>T; NP_001954.2:p.(Pro1070Leu); rs121434567.

The substitution affects the second proline in the cytoplasmic PKNP/PXXP basolateral-sorting motif of pro-EGF. It disrupts basolateral—but not apical—delivery/release in polarized epithelial cells. [257]

2.2 Risk and protective factors

Loop and thiazide diuretics increase urinary magnesium loss, while prolonged PPI treatment, poor intake, alcoholism, and gastrointestinal disease may further lower magnesium status. [333] EGFR inhibitors are especially mechanistically relevant because cetuximab, panitumumab, and related drugs reproduce renal magnesium wasting by interrupting the same pathway. [336]

2.3 Gene–environment interaction

The genotype reduces the kidney’s reserve capacity to conserve magnesium. Accordingly, low dietary intake, diarrhea, vomiting, alcohol-associated depletion, or magnesium-wasting medication should produce a larger fall in serum magnesium than in an unaffected person. This interaction is physiologically plausible but has not been studied directly in HOMG4 patients.

Conversely, dietary magnesium restriction induces compensatory renal TRPM6 expression in wild-type mice; that compensation may be inadequate when upstream EGF–EGFR signaling is defective. [310]

No infectious, toxic, occupational, radiation, or immune cause of the Mendelian disorder has been identified.

3. Phenotypes

3.1 Human phenotype table

Frequencies below refer to the only two published molecularly confirmed patients and therefore must not be interpreted as robust estimates.

The original clinical observations included seizures, mild-to-moderate psychomotor retardation and brisk reflexes. [153] The molecular reassessment documented serum magnesium of 0.53–0.66 mmol/L and fractional magnesium excretion of 4.8% and 3.6%. [164]

3.2 Interpretation of neurologic disease

It remains uncertain whether developmental impairment results entirely from early, recurrent hypomagnesemic seizures or whether altered EGF signaling contributes directly to brain development. The original study detected EGF expression in human cerebrum, but no patient neuroimaging, neuropathology, or brain-specific functional study established a direct developmental mechanism. Therefore:

• Renal magnesium wasting: demonstrated upstream phenotype.
• Seizures: strongly compatible with magnesium-dependent neuronal hyperexcitability.
• Developmental delay/intellectual disability: associated consistently in the two patients, but exact causal path is partly inferred.

No disease-specific EQ-5D, SF-36, PROMIS, educational, caregiver-burden, or other quality-of-life data are available.

4. Genetic and molecular information

4.1 Gene and protein

NCBI describes EGF as a precursor processed into a 53-amino-acid peptide that binds EGFR and regulates cellular proliferation and differentiation. [91] UniProt records p.Pro1070Leu as affecting basolateral sorting and preventing effective EGFR/TRPM6 stimulation. [94]

4.2 Pathogenic variant

The complete ClinVar record confirms the coordinates, frequencies and single literature-only pathogenic submission. [106] The very low population frequency is compatible with recessive disease, but ClinVar’s classification is not an expert-panel or multi-laboratory consensus.

4.3 Segregation and penetrance

Both affected sisters were homozygous. Both parents, two unaffected sisters, and a paternal aunt were heterozygous; two children of the aunt were homozygous reference. This is consistent with high penetrance for the homozygous state and nonpenetrance in heterozygotes, but only two homozygotes are known.

No data establish:

• penetrance percentage;
• age-dependent penetrance;
• allelic series or genotype–phenotype correlation;
• germline mosaicism;
• anticipation;
• a founder mutation;
• modifier genes;
• somatic disease causation;
• disease-specific DNA methylation, histone or chromatin abnormalities;
• recurrent copy-number or chromosomal structural abnormalities.

Assuming Hardy–Weinberg equilibrium and an allele frequency of 2–3×10⁻⁵, a purely illustrative carrier frequency would be about 4–6×10⁻⁵ and homozygous frequency approximately 4–9×10⁻¹⁰. This estimate is uncertain because ancestry-specific frequency, pathogenicity, ascertainment, and founder effects are inadequately characterized.

5. Environmental information

Renal hypomagnesemia 4 is genetic, not environmentally caused. Clinically relevant exacerbating factors include:

There is no evidence for smoking, exercise, pollution, radiation, occupational exposure, or infectious-agent involvement specific to HOMG4.

6. Mechanism and pathophysiology

6.1 Ordered causal chain

1. Homozygous EGF c.3209C>T causes p.Pro1070Leu in the cytoplasmic tail of pro-EGF.
2. p.Pro1070Leu disrupts a PXXP basolateral-sorting motif and leads to reduced basolateral delivery/release of pro-EGF in polarized distal-tubule epithelium; apical release remains relatively preserved.
3. Reduced basolateral EGF leads to inadequate activation of basolateral EGFR on distal convoluted tubule epithelial cells.
4. Reduced EGFR signaling leads to reduced Src/PI3K–Rac1 and MEK–ERK/AP-1 signaling, based primarily on subsequent cell studies.
5. Reduced Src/Rac1 signaling leads to less trafficking and surface abundance of TRPM6/TRPM7-containing channels at the apical membrane; reduced ERK/AP-1 signaling may additionally lower TRPM6 transcription.
6. Reduced apical TRPM6 activity leads to impaired transcellular Mg²⁺ entry from tubular fluid into DCT epithelial cells.
7. Impaired DCT magnesium reabsorption results in inappropriately high urinary magnesium excretion despite hypomagnesemia.
8. Persistent urinary loss leads to systemic magnesium depletion.
9. Systemic magnesium depletion leads to neuronal and neuromuscular hyperexcitability, producing brisk reflexes, tetany and generalized seizures.
10. Early recurrent seizures and/or altered EGF signaling are inferred to contribute to psychomotor delay and moderate intellectual disability; the relative contributions have not been demonstrated.
11. Potential branch: severe magnesium deficiency may lead to myocardial electrical instability and arrhythmia, although arrhythmia has not been reported in the two HOMG4 patients.

6.2 Experimental support

The 2007 study showed:

• EGF colocalization with NCC-positive distal convoluted tubules in rat kidney.
• Dose-dependent EGF stimulation of TRPM6 current in transfected HEK293 cells, with an EC₅₀ of approximately 1.7 nM.
• Wild-type but not p.Pro1070Leu conditioned medium stimulated TRPM6.
• Cetuximab reduced wild-type EGF-induced current from 491 ± 62 to 286 ± 48 pA/pF, versus 191 ± 22 pA/pF with mock medium.
• In polarized MDCK cells, mutant and wild-type apical media stimulated TRPM6 similarly, but mutant basolateral medium did not.
• Cetuximab-treated patients developed renal magnesium wasting, providing a human pharmacologic phenocopy. [113]

A later primary study reported that EGFR activation recruits Src-family kinases and Rac1, redistributing vesicular TRPM6 to the plasma membrane. PMID associated with JASN 2009; DOI 10.1681/ASN.2008030327. [241] Another study found EGF-dependent increases in phospho-ERK1/2, c-Fos, c-Jun and TRPM6 transcription, supporting an ERK/AP-1 branch; PMID 19937979, published online November 2009. [244]

6.3 Current mechanistic interpretation and uncertainty

Recent renal-magnesium reviews continue to place EGF upstream of TRPM6/TRPM7-mediated DCT reabsorption. A 2023 review states that EGF increases TRPM6 membrane expression and transcription and acts as a paracrine DCT regulator. [232] The 2024 Core Curriculum similarly describes DCT magnesium reabsorption through TRPM6/TRPM7 heteromers and paracrine regulation by EGF. [228]

However, complete Egf knockout mice do not develop significant hypomagnesemia, indicating species differences, ligand redundancy, developmental compensation, or a variant effect more complex than simple EGF absence. [305] Thus, the human p.Pro1070Leu mechanism is best described as abnormal polarized pro-EGF sorting/processing, not proven generic EGF haploinsufficiency.

6.4 Suggested ontology annotations

The correct DCT epithelial-cell identifier is CL:1000849. [196] GO:0010960 denotes magnesium-ion homeostasis, while GO:0016323 and GO:0016324 identify basolateral and apical plasma membranes. [426][427]

6.5 Omics and advanced technologies

No HOMG4-specific patient transcriptomic, proteomic, metabolomic, lipidomic, single-cell, spatial-transcriptomic, CRISPR-screen, organoid, iPSC or integrated multi-omics study was found. Current single-cell kidney atlases recognize DCT epithelial cells and markers such as SLC12A3 and TRPM6, but this is normal-reference annotation rather than disease profiling. [206]

7. Anatomical structures affected

The DCT corresponds to UBERON:0001292 and its epithelial cells to CL:1000849. [202][200] The disease is systemic and bilateral by virtue of a germline defect; unilateral or asymmetric renal involvement is not expected.

8. Temporal development

• Genetic onset: conception.
• Biochemical onset: probably early life; exact neonatal magnesium values are unavailable.
• Clinical onset: generalized seizures in the first year of life.
• Development: psychomotor delay became evident during childhood.
• Adult course: both women had moderate intellectual disability; chronic hypomagnesemia persisted.
• Pattern: chronic renal wasting with potentially episodic neurologic decompensation when magnesium falls further.
• Progression: no staged progressive nephropathy, nephrocalcinosis or renal failure was reported.
• Remission: no spontaneous biochemical remission documented.
• Critical period: infancy and early childhood, when seizures and magnesium deficiency may have disproportionate neurodevelopmental consequences.
• Duration: presumed lifelong.

No formal natural-history staging system or longitudinal cohort exists.

9. Inheritance and population characteristics

Current Orphanet prevalence is below one per million. [134] A review emphasizes that only two affected girls from one consanguineous family have been reported. [380]

For two carrier parents, standard autosomal-recessive recurrence probabilities are 25% affected, 50% carrier, and 25% unaffected/noncarrier per pregnancy, assuming both parental variants are confirmed and fully penetrant.

10. Diagnostics

10.1 Recommended diagnostic workflow

1. Confirm persistent low total serum magnesium; consider ionized magnesium if available.
2. Measure serum calcium, potassium, bicarbonate, creatinine/eGFR, phosphate, PTH, glucose and albumin.
3. Obtain urine magnesium and creatinine, ideally before major replacement.
4. Calculate fractional magnesium excretion:

[ FE_{Mg}=\frac{U_{Mg}\times P_{Cr}}{0.7\times P_{Mg}\times U_{Cr}}\times100 ]

1. In hypomagnesemia, an FEMg above approximately 3–4% supports renal wasting; below 2% suggests an extrarenal source. A 24-hour urinary magnesium above approximately 30 mg/day also supports renal loss. [136]
2. Document serum and urinary calcium. HOMG4 is expected to be normocalcemic and normocalciuric.
3. Exclude acquired causes, particularly diuretics, aminoglycosides, platinum chemotherapy, calcineurin inhibitors, EGFR inhibitors, alcohol misuse and uncontrolled diabetes.
4. Pursue molecular testing when onset is infantile, the condition is familial or unexplained, or neurologic manifestations coexist.
5. Confirm candidate variants with parental segregation and interpret under current ACMG/AMP criteria.

10.2 Genetic testing

Orphanet lists postnatal molecular testing panels containing EGF and other primary-hypomagnesemia genes. [126]

10.3 Clinical and ancillary tests

• ECG: particularly during severe hypomagnesemia, palpitations or syncope.
• EEG: for seizure classification and monitoring.
• Renal ultrasound: not diagnostic; useful if hypercalciuria or nephrocalcinosis suggests another disorder.
• Brain MRI: may evaluate developmental delay or refractory seizures but no HOMG4-specific imaging pattern is known.
• Biopsy: no diagnostic role.
• Urinary EGF: biologically attractive but not validated as a HOMG4 diagnostic biomarker.

10.4 Differential diagnosis

The combination of urine/serum biochemistry, inheritance and extrarenal manifestations guides differential testing. Hypercalciuria suggests TAL disorders, whereas hypokalemia and metabolic alkalosis suggest Gitelman-like DCT disease. [319]

No newborn screening program or standardized clinical diagnostic criteria exist. Cascade biochemical and genetic testing is appropriate for relatives.

11. Outcome and prognosis

Disease-specific survival, mortality, five-year survival and life-expectancy statistics are unavailable. Both original patients survived into adulthood, suggesting that the condition is not inevitably fatal when seizures and electrolyte abnormalities are managed.

Important morbidity includes:

• recurrent infantile seizures;
• permanent developmental and cognitive disability;
• chronic treatment and monitoring burden;
• potential tetany, muscle spasm and weakness;
• potential cardiac arrhythmia when magnesium is severely low.

Severe hypomagnesemia can cause torsades de pointes and other fatal arrhythmias, although none were documented in the HOMG4 sisters. [346]

Prognostic factors are inferred to include:

• age at recognition;
• depth and duration of magnesium deficiency;
• seizure burden;
• response and adherence to magnesium replacement;
• exposure to magnesium-wasting drugs;
• renal function;
• coexisting hypokalemia or hypocalcemia.

No validated prognostic biomarker or disease-specific quality-of-life instrument exists. Serum magnesium, FEMg, seizure frequency, EEG findings and developmental trajectory are practical monitoring endpoints.

12. Treatment

No treatment corrects the inherited pro-EGF trafficking defect. Management is supportive and extrapolated largely from general hypomagnesemia and other renal magnesium-wasting disorders.

12.1 Treatment approach

For acute unstable adult hypomagnesemia, general guidance uses 1–2 g magnesium sulfate over approximately 15 minutes, while nonemergent replacement may use 4–8 g over 12–24 hours; pediatric dosing requires weight-based specialist protocols. [165] Oral therapy is generally divided to reduce diarrhea, with careful dose reduction and monitoring when eGFR is below 30 mL/min/1.73 m².

Amiloride raised serum magnesium, lowered FEMg and improved symptoms in one patient with idiopathic renal magnesium wasting, but this is indirect evidence. [287] Continuous home subcutaneous magnesium sulfate at 2 g/day normalized or nearly normalized serum magnesium in a refractory renal-wasting case, again not HOMG4-specific. [176]

12.2 Treatment limitations and adverse effects

• Oral magnesium commonly causes diarrhea and abdominal discomfort.
• Rapid IV magnesium can cause flushing, hypotension, bradycardia and respiratory depression.
• Hypermagnesemia is a risk with impaired kidney function.
• Amiloride may cause hyperkalemia, hypotension and renal-function deterioration.
• Magnesium replacement may remain incomplete because renal losses continue.
• Magnesium correction should not automatically replace antiseizure treatment once epilepsy is established.

12.3 Experimental and precision therapies

No registered HOMG4-specific interventional trial, gene therapy, RNA therapy, CRISPR treatment, cell therapy or recombinant EGF treatment was identified. Systemic EGF or EGFR agonism would carry substantial proliferative and oncologic concerns and is not an established treatment.

A future precision approach would require kidney/DCT-targeted restoration of correctly polarized EGF signaling or enhancement of TRPM6 surface expression without systemic mitogenic EGFR activation. This remains conceptual.

13. Prevention

Primary prevention

The inherited genotype cannot be prevented after conception. Reproductive options include:

• carrier testing of at-risk relatives;
• partner testing;
• preimplantation genetic testing for monogenic disease;
• chorionic-villus or amniotic-fluid prenatal diagnosis when familial variants are known;
• donor gametes or other family-planning options.

Secondary prevention

• Cascade testing in siblings and relatives.
• Serum magnesium measurement in at-risk infants, especially before seizures occur.
• Early urine magnesium/FEMg assessment.
• Prompt genetic testing for familial infantile hypomagnesemia.
• Early developmental and neurologic assessment.

Tertiary prevention

• Maintain serum magnesium at the highest safely achievable level.
• Prevent prolonged or recurrent seizures.
• Monitor ECG and associated potassium/calcium abnormalities during severe episodes.
• Avoid preventable magnesium-wasting drugs, especially EGFR inhibitors where alternatives exist.
• Ensure adequate dietary magnesium and treat diarrhea or malabsorption.
• Provide early-intervention, educational and rehabilitation services.

No vaccine, antimicrobial prophylaxis, public-health sanitation intervention or population newborn-screening program applies.

14. Other species and natural disease

MGI records one-to-one vertebrate orthology among human, mouse, rat and zebrafish and mouse Egf NCBI Gene 13645. [271] No OMIA entry, breed predisposition, veterinary founder variant, zoonotic transmission or cross-species infectious risk was identified. The mechanism is evolutionarily relevant but the specific human disease does not appear to be a recognized natural veterinary disorder.

15. Model organisms and experimental systems

The absence of hypomagnesemia in Egf knockout mice is a major model limitation and argues for creation of a precise p.Pro1070Leu knock-in, rather than assuming that complete knockout is equivalent to the human trafficking mutation. [305]

Recent developments and research priorities

No new molecularly confirmed HOMG4 family or independently validated pathogenic EGF allelic series was found through the 2023–2024 literature. Recent work instead strengthens and refines the broader renal-magnesium framework:

1. 2023 physiology update: DCT magnesium fine-tuning is now commonly modeled through TRPM6/TRPM7 heteromeric channels, with EGF regulating membrane abundance and transcription rather than acting simply as a channel opener. [232]
2. 2024 Core Curriculum: confirms EGF as a paracrine regulator of DCT TRPM6/TRPM7 and provides contemporary biochemical diagnostic thresholds. [228]
3. 2024 human biomarker research: urinary EGF is increasingly interpreted as a marker of distal tubular mass and correlates with serum magnesium and kidney outcomes, but it is not yet validated for HOMG4 diagnosis or monitoring. [184]
4. Model discrepancy: Egf-null mice lack the expected severe magnesium phenotype, so human variant-specific trafficking, redundant EGFR ligands, or species-specific DCT physiology require clarification. [305]
5. Needed studies: independent patients, modern ACMG/ClinGen gene–disease curation, ancestry-resolved variant frequencies, patient-derived DCT organoids, knock-in animal models, prospective magnesium-replacement outcomes, neurodevelopmental natural history and disease-specific quality-of-life assessment.

Overall evidence assessment

The clinical phenotype and biochemical defect are well documented in two related humans, and the original p.Pro1070Leu functional experiments provide a coherent mechanism. Nevertheless, the gene–disease relationship remains constrained by a single family, a single variant, no independent replication, an old single-submitter ClinVar assertion, and a discordant Egf-knockout mouse phenotype. The best current interpretation is therefore:

Renal hypomagnesemia 4 is a highly plausible, functionally supported autosomal-recessive pro-EGF polarized-trafficking disorder, but its full allelic spectrum, penetrance, epidemiology, natural history and optimal treatment remain undetermined.

Reference Validation

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All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

• MONDO:0012717 (2 mentions) - the report calls it "MONDO"; MONDO calls it renal hypomagnesemia 4
• DOID:0060882 (1 mention) - the report calls it "Disease Ontology"; DOID calls it renal hypomagnesemia 4
• CL:4030016 (1 mention) - the report calls it "Early DCT epithelial cell"; CL calls it epithelial cell of early distal convoluted tubule
• NCIT:C623 (2 mentions) - the report calls it "Evidence from unrelated refractory cases, not HOMG4"; NCIT calls it Magnesium Sulfate

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

• GO:0005154 (1 mention) - the report calls it "EGF receptor binding"; GO calls it epidermal growth factor receptor binding, and lists "EGF receptor binding" among its other names
• CHEBI:18420 (1 mention) - the report calls it "Magnesium ion"; CHEBI calls it magnesium(2+), and lists "MAGNESIUM ION" among its other names
• CL:1000849 (4 mentions) - the report calls it "DCT epithelial cell"; CL calls it kidney distal convoluted tubule epithelial cell

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA, Gene, MGI.