Information about Inherited Sick Sinus Syndrome

Hi,

I would like to know what are the probabilities of inherit my heart disease to my descendants.

I have sinus bradycardia since I was 17 years old, due to sick sinus syndrome that I have inherited from my mother who has it since whe was 12.  

  How can I tell if it is autosomal recessive or dominant?

  We both have a pacemaker, and I just have my second pacemaker reimplanted (don't know if that's a correct expression).

  There's no much information on internet or books.
  I have heard that is a problem that is passed from the mother to the female daughter and not to the male son? I have a brother and he hasn't have any symptoms or previous altered tests. Should he be worried? could he carry the defect and inherit it to his children?
   If you have any suggestions about any bibliography I could consult, it´ll be also very appeciated.
   Thank you very much for your time.

                                Virginia.

[Joseph Sclafani, M.D.]

Thank you for your question. I would be happy to tell you more about what is known about the genetics of sick sinus syndrome (SSS). References are placed in parenthesis.

Small studies of patients with idiopathic SSS have so far implicated three genes—SCN5A, HCN4, and ANKB. They code for the following proteins: Cardiac sodium channel alpha subunit (NaV1.5), Hyperpolarization-activated cyclic nucleotide-gated channel 4 gene, and the Ankyrin-B protein, respectively. There are 15 different SSS-associated mutations have been reported in SCN5A. These mutations in the genes produced either lack of expression (production) of these channels or channels that didn’t function properly (loss of function). In one study (1), was looked at as a candidate for the cause of familial SSS among 10 pediatric patients in 7 families. They found evidence suggesting autosomal recessive transmission when looking at mutations from this gene.  As for the HCN4 gene, 2 different types of mutations were identified in the literature (2). But data on the type of transmission is not available at this time. Similarly, a mutation for the ANKB gene has been identified, but the exact type of genetic transmission of this gene is not known.

In summary, the precise genetic transmission of the SSS is not entirely known because it is due to many different types of genetic mutations. One of the more common genetic mutations, SCN5A, appears to follow an autosomal recessive pattern. However, there are other mutations with unknown types of transmissions with variable penetrance. Penentrance is the degree to which someone who has the abnormal gene (has the genotype) develops symptoms (phenotype expression). More research on this topic needs to be done in the coming years.

Bibliography
1. Benson DW, Wang DW, Dyment M, et al: Congenital sick sinus syndrome caused by recessive mutations in the cardiac sodium channel gene (SCN5A).  J Clin Invest  2003; 112:1019
2. Ueda K, Nakamura K, Hayashi T, et al: Functional characterization of a trafficking-defective HCN4 mutation, D553N, associated with cardiac arrhythmia.  J Biol Chem  2004; 279:27194.
3. Le Scouarnec S, Bhasin N, Vieyres C, et al: Dysfunction in ankyrin-B–dependent ion channel and transporter targeting causes human sinus node disease.  Proc Natl Acad Sci U S A  2008; 105:15617-15622.