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Condition report · Neurological

Hypopigmentation, Organomegaly and Delayed Myelination (HOD)

Whole genome sequencing reads the CLCN7 gene for changes that cause HOD, a very rare condition with lighter skin and hair, an enlarged liver and spleen, and delayed brain development.

A condition report looks for rare variants known to cause the conditions it covers.

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About this condition

A very rare condition causing light skin and hair, an enlarged liver and spleen, and delayed brain development. It is caused by a specific new change in the CLCN7 gene that makes a chloride channel in lysosomes overactive.

Hypopigmentation, organomegaly and delayed myelination (HOD) is a very rare condition. People have lighter than usual skin and hair, an enlarged liver and spleen, and delayed development. Brain imaging shows delayed myelination, and only a few people have been reported.

HOD is caused by a specific change in one copy of the CLCN7 gene, such as p.Tyr715Cys, which has arisen new in the reported cases. CLCN7 makes a chloride channel in lysosomes, which are compartments inside cells. The change makes the channel overactive, which enlarges the lysosomes and causes material to build up in many tissues.

Other CLCN7 changes cause osteopetrosis, a separate bone condition that is not seen in HOD. Care is supportive, with developmental therapies and monitoring of the liver and spleen. Because the change has arisen new in reported cases, recurrence risk is low, but parental testing and genetic counselling are recommended.

The condition we analyse

Hypopigmentation, Organomegaly and Delayed Myelination and Development

Autosomal dominant · Only a few people have been reported.

Caused by gain-of-function changes in one copy of CLCN7, such as p.Tyr715Cys, which has arisen de novo in reported cases. The overactive channel enlarges lysosomes and causes storage in many tissues. Other CLCN7 changes cause osteopetrosis, a separate bone condition not seen in HOD.

Signs and symptoms

Developmental delay. Skin and hair are lighter than usual, and the liver and spleen are enlarged. Brain imaging shows delayed myelination.

What a diagnosis changes

Care is supportive, with developmental therapies and monitoring of the liver and spleen. The change has arisen de novo in reported cases, so recurrence risk is low, but parental testing and genetic counselling are recommended.

Genes analysed

Also known as

HOD

MONDO:0032805OMIM 618541MedGen 1684826Sources: [1][2]

Why whole genome sequencing

In reported cases the HOD change arose new, so parental testing helps clarify the risk to the family. Whole genome sequencing reads CLCN7 in the same test.

Different CLCN7 changes, different conditions

Changes in CLCN7 can cause very different conditions depending on their effect on the channel. HOD is caused by an overactive channel, while other CLCN7 changes cause osteopetrosis, which is not seen in HOD.

Family testing is still recommended

Because the change has arisen new in reported cases, recurrence risk is described as low. Parental testing and genetic counselling are still recommended for each family, and developmental care and liver and spleen monitoring continue as part of care.

References

  1. Polovitskaya MM, Rana T, Ullrich K, Murko S, Bierhals T, Vogt G et al., 2024. Gain-of-function variants in CLCN7 cause hypopigmentation and lysosomal storage disease. The Journal of biological chemistry
  2. CLCN7 gene. MedlinePlus Genetics

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