Adult-onset familial hypomagnesaemia with secondary hypocalcaemia (HOMG1) due to a novel TRPM6 variant was managed long-term with parenteral magnesium supplementation, with intravenous administration effective for over 3 years before device infections and venous occlusions necessitated transition to subcutaneous infusion.
Key Findings
Background
A man in his late 50s was diagnosed with adult-onset familial hypomagnesaemia with secondary hypocalcaemia (HOMG1, OMIM #602014) due to a novel TRPM6 variant.
The patient presented with muscle cramps due to severe hypomagnesaemia
HOMG1 is caused by impaired gastrointestinal magnesium absorption
The diagnosis was established following extensive evaluation
The TRPM6 variant identified was described as novel
Results
Oral magnesium supplementation was insufficient to maintain stable serum magnesium concentrations in this patient.
Insufficiency of oral supplementation was attributed to impaired gastrointestinal absorption characteristic of HOMG1
Inadequate oral supplementation led to recurrent emergency department presentations
The failure of oral supplementation necessitated alternative supplementation routes
Results
Intravenous magnesium administered twice weekly was effective for over 3 years.
Intravenous magnesium was given two times a week
This regimen was effective for over 3 years
Device infections and venous occlusions ultimately rendered intravenous access unfeasible
These complications necessitated a transition to an alternative route of administration
Results
Subcutaneous magnesium infusion provided an alternative route when intravenous access became unfeasible.
Subcutaneous infusion was initiated after intravenous access was no longer feasible due to device infections and venous occlusions
Local pain at the infusion site required concomitant use of anaesthetics
Recurrent allergic reactions to the anaesthetic agents introduced additional challenges
The subcutaneous route represented a viable but complex alternative
Discussion
This case illustrates a rare presentation of HOMG1 with adult onset, contrasting with the typically pediatric presentation of the condition.
The patient presented in his late 50s, representing an adult-onset case
HOMG1 is typically recognized earlier in life
Hypomagnesaemia is described as a common clinical finding, often secondary to proton pump inhibitor use or excessive alcohol use
The case highlights challenges in long-term parenteral magnesium supplementation management
Bogaert E, Hartjes K, Boots J. (2026). Chronic magnesium supplementation in a patient with relapsing severe hypomagnesaemia due to a novel TRPM6 variant diagnosed in adulthood.. BMJ case reports. https://doi.org/10.1136/bcr-2025-268968