Niemann-pick types a/b

Inheritance

How is Niemann-Pick disease (SMPD1-associated) inherited?

We each have 2 copies of the SMPD1 gene, one we inherit from our mother and one from our father. We only need 1 copy of the SMPD1 gene to work in order for our cells to work properly. In order to have Niemann-Pick disease (SMPD1-associated), both copies of the SMPD1 gene need to have changes or mutations that make the gene not work properly. This is called "autosomal recessive" inheritance. The changes in the two copies of the SMPD1 gene can be the same change or different type of changes/mutations. As long as both changes make the gene work less or not at all, the person will have Niemann-Pick disease (SMPD1-associated).

Someone who only has 1 change/mutation in SMPD1 is known as a "carrier." Therefore, the parents of a person with Niemann-Pick disease (SMPD1-associated) are both carriers of a change in the SMPD1 gene. When both parents are carriers, there is a 25% chance with each child that they will inherit both non-working copies of the SMPD1 gene and develop Niemann-Pick disease. Additionally, each child will have a 50% chance to inherit one copy of the non-working SMPD1 gene and also be a carrier.

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What does it mean to have inherited a "variant" in the gene for Niemann-Pick disease (SMPD1-associated)?

Are there forms of Niemann-Pick Disease (SMPD1-associated) that are not genetic?

Do different changes/mutations in SMPD1 cause different symptoms or different types of Niemann-Pick disease (SMPD1-associated)?

What does it mean to have inherited a "variant" in the gene for Niemann-Pick disease (SMPD1-associated)?

Everyone has spelling differences in their genes. That's what makes us all different. A "variant" is a genetic spelling difference in its code that has never been seen before or is not understood very well. If you have inherited a "variant of uncertain significance" in the SMPD1 gene, it means that there is a difference in how your gene is spelled, but that we don't yet know if this difference makes the gene work less or if it is just the way your gene is normally spelled and does not cause disease. More information or data is needed in order to understand how this variant affects the gene.

Since Niemann-Pick disease (SMPD1-associated) is caused by spelling changes in both copies of the SMPD1 gene, it is possible to see someone who has one variant of uncertain significance and one known mutation (spelling change known to cause disease), or even someone with 2 variants of uncertain significance. If this person is having symptoms of Niemann-Pick disease (SMPD1-associated), it makes it more likely that the variants are spelling differences that make the gene work less and are possibly mutations. If they are not having symptoms, it makes it more likely that this is just a normal spelling difference and a benign variant (not linked to disease).

Are there forms of Niemann-Pick Disease (SMPD1-associated) that are not genetic?

No, all forms of Niemann-Pick disease (SMPD1-associated) are genetic. They are caused by changes/mutations that most of the time are identified in the SMPD1 gene.

Do different changes/mutations in SMPD1 cause different symptoms or different types of Niemann-Pick disease (SMPD1-associated)?

When specific types of changes/mutations in a gene cause specific symptoms, this is known as a "genotype-phenotype" correlation. There are genotype-phenotype correlations associated with Niemann-Pick disease (SMPD1-associated):

  • p.Arg610del: having 2 copies of this change is associated with mild symptoms of type B
  • p.Leu139Pro, p.Ala198Pro, and p.Arg476Trp may cause less severe forms of type B
  • p.His423Tyr and p.Ls578Asn cause type A

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