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PubMed This is a summary of 40 peer-reviewed journal articles Updated
Medical Genetics · Familial Hypomagnesemia with Secondary Hypocalcemia

Familial hypomagnesemia with secondary hypocalcemia (HSH): A Patient Guide

At a Glance

Familial hypomagnesemia with secondary hypocalcemia (HSH) is an inherited condition in which TRPM6 changes severely limit the body’s absorption of magnesium, causing low calcium as well. Lifelong oral magnesium, monitoring, and a sick-day plan help protect children’s health, though outcomes vary.

Familial hypomagnesemia with secondary hypocalcemia (HSH, or HOMG1) is an ultra-rare genetic condition that fundamentally changes how the body handles one of its most essential minerals. At its core, HSH is caused by mutations in the TRPM6 gene, which serves as a channel for magnesium active absorption in the intestinal lining. Because this channel is impaired, the body’s active absorption of magnesium from the diet is severely reduced, leading to a profound deficiency that affects nearly every system in the body [1][2].

For most families, the discovery of HSH begins with a medical crisis in early infancy. Because magnesium acts as a “master switch” that controls other minerals, its deficiency blunts the response of the parathyroid glands, causing a rapid drop in calcium levels which can lead to neonatal seizures and severe muscle spasms [3][4]. This hallmark presentation—low magnesium and low calcium occurring together—is the key signal that helps doctors distinguish HSH from more common forms of epilepsy or endocrine disorders [5].

Living with HSH requires a lifelong commitment to high-dose oral magnesium therapy. Because the body’s natural active absorption is impaired, treatment relies on careful, individualized daily supplementation to increase blood magnesium enough to keep the brain and heart stable [6][5]. While this requires careful monitoring and navigating digestive side effects (like osmotic diarrhea, or vomiting during illness which requires an urgent sick-day plan), the focus of care is always on clinical wellness: ensuring the child is seizure-free, growing well, and meeting their developmental milestones [7][8].

The path forward for a child with HSH is one of resilience and careful management. Although it is a chronic, inherited condition, the long-term outlook for children who are able to adhere strictly to their treatment plan is generally encouraging, though outcomes vary [9][10]. By working closely with a specialized care team, families can navigate the complexities of this rare diagnosis and support their child in living a full, active life [11].

In this guide

6 chapters

01

Understanding Your Child's HSH Diagnosis

Learn how familial hypomagnesemia with secondary hypocalcemia causes infant seizures, why magnesium affects calcium, and how TRPM6 testing confirms HSH.

02

Symptoms & Emergencies in HSH

Learn HSH warning signs in familial hypomagnesemia with secondary hypocalcemia, including seizures, breathing problems, and when to seek care for your child.

03

The Biology of HSH: The Magnesium and Calcium Connection

Learn how TRPM6 mutations cause familial hypomagnesemia with secondary hypocalcemia, why calcium falls, how HSH is inherited, and which disorders can mimic it.

04

Lab Tests & Genetic Testing: Understanding Your Child's Report

Learn how blood, urine, FEMg, PTH, and TRPM6 testing help diagnose familial hypomagnesemia with secondary hypocalcemia and clarify your child's results.

05

Standard of Care: Managing Magnesium Daily

Learn how familial hypomagnesemia with secondary hypocalcemia is treated, including IV rescue, daily magnesium, calcium monitoring, side effects, and safety.

06

Living with HSH: The Path Forward

Learn about long-term care for primary hypomagnesemia with secondary hypocalcemia, including development, sibling screening, and family coping at home.

Common questions in this guide

What causes familial hypomagnesemia with secondary hypocalcemia?
HSH is caused by mutations in the TRPM6 gene, which normally helps the intestine absorb magnesium from food. When this channel does not work properly, severe magnesium deficiency can reduce the parathyroid glands’ response and cause low calcium.
What symptoms can HSH cause in babies?
HSH often becomes apparent in early infancy when low magnesium and low calcium lead to seizures or severe muscle spasms. This combination can help clinicians distinguish HSH from more common causes of seizures.
How is HSH treated in children?
Treatment usually requires lifelong, high-dose oral magnesium tailored to the child’s needs. The care team monitors magnesium levels and the child’s clinical health, including seizure control, growth, and development; digestive side effects such as diarrhea may require adjustments.
What should we do if a child with HSH vomits or has diarrhea?
Vomiting or diarrhea can make it difficult to keep magnesium medicine down or absorb enough of it. Families should have a written sick-day plan from the treating team and seek urgent medical guidance when the child cannot keep the medication down.
What is the long-term outlook for a child with HSH?
HSH is a chronic inherited condition, but the outlook is generally encouraging for children who follow their magnesium treatment plan closely. Outcomes vary, and ongoing care focuses on preventing seizures, supporting growth, and tracking development.
How will we know when a child’s magnesium dose needs to change?
The treating team should reassess a child’s magnesium needs as they grow and review blood levels, symptoms, side effects, and overall health. Families should discuss dose changes with the care team rather than adjusting the medicine on their own.

Get notified when new evidence is published on Primary hypomagnesemia with secondary hypocalcemia.

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References

References (11)
  1. 1

    Case Report: A Novel Non-Canonical Splice Site Variant (c.1638+7T>C) in TRPM6 Cause Primary Homagnesemia With Secondary Hocalcemia.

    Song J, Lei J, Zhang J, et al.

    Frontiers in pediatrics 2022; (10()):834241 doi:10.3389/fped.2022.834241.

    PMID: 35692977
  2. 2

    Case Report: Novel TRPM6 Mutations Cause Hereditary Hypomagnesemia With Secondary Hypocalcemia in a Chinese Family and a Literature Review.

    Han Y, Zhao Y, Wang H, Huo L

    Frontiers in pediatrics 2022; (10()):912524 doi:10.3389/fped.2022.912524.

    PMID: 35903165
  3. 3

    Clinical Spectrum of Primary Hypomagnesemia with Secondary Hypocalcemia due to TRPM6 Mutation.

    Aftab S, Anjum MN, Aslam N, et al.

    Hormone research in paediatrics 2026; (99(7)):1045-1050 doi:10.1159/000547303.

    PMID: 40853861
  4. 4

    Familial hypomagnesemia with hypocalcemia: a rare cause of infantile seizures.

    Srinivasan R, Ninama AC, Krishna S, Vasudevan A

    CEN case reports 2023; (12(2)):139-145 doi:10.1007/s13730-022-00734-x.

    PMID: 36131192
  5. 5

    Hypomagnesemia and functional hypoparathyroidism due to novel mutations in the Mg-channel TRPM6.

    Astor MC, Løvås K, Wolff AS, et al.

    Endocrine connections 2015; (4(4)):215-22 doi:10.1530/EC-15-0066.

    PMID: 26273099
  6. 6

    Treatment Difficulties in Hypomagnesemia Secondary to the Transient Receptor Potential Melastatin 6 Gene: A Case Report with Novel Mutation

    Yücel H, Genç Sel Ç, Kasapkara ÇS, et al.

    Journal of clinical research in pediatric endocrinology 2021; (13(1)):114-118 doi:10.4274/jcrpe.galenos.2020.2020.0004.

    PMID: 32302086
  7. 7

    Three cases of hereditary hypomagnesemia with secondary hypocalcemia caused by novel TRPM6 gene mutations and a literature review.

    Yang M, Zheng Z, Shan X, Luo Y

    Journal of pediatric endocrinology & metabolism : JPEM 2026; (39(9)):917-925 doi:10.1515/jpem-2026-0185.

    PMID: 42324811
  8. 8

    A novel TRPM6 variant (c.3179T>A) causing familial hypomagnesemia with secondary hypocalcemia.

    Lomelino-Pinheiro S, Margarida B, Lages AS

    Endocrinology, diabetes & metabolism case reports 2020; (2020()).

    PMID: 32369769
  9. 9

    Long-term Clinical Follow-up of Patients with Familial Hypomagnesemia with Secondary Hypocalcemia

    Bayramoğlu E, Keskin M, Aycan Z, et al.

    Journal of clinical research in pediatric endocrinology 2021; (13(3)):300-307 doi:10.4274/jcrpe.galenos.2021.2020.0192.

    PMID: 33565749
  10. 10

    A Novel Homozygous Mutation in the Transient Receptor Potential Melastatin 6 Gene: A Case Report.

    Altıncık A, Schlingmann KP, Tosun MS

    Journal of clinical research in pediatric endocrinology 2016; (8(1)):101-4 doi:10.4274/jcrpe.2254.

    PMID: 26759217
  11. 11

    Genetic Testing in the Pediatric Nephrology Clinic: Understanding Families' Experiences.

    Nevin SM, McLoone J, Wakefield CE, et al.

    Journal of pediatric genetics 2022; (11(2)):117-125 doi:10.1055/s-0040-1721439.

    PMID: 35769952

This guide explains familial hypomagnesemia with secondary hypocalcemia for informational purposes only and does not constitute medical advice. A child’s magnesium dose, monitoring, and sick-day plan should be set with the treating care team.