chromosone 5 31 to 33.1 denovo and SMA

[lilviathan]

Hi. Thank you for your help.  My son is 21 and has muscle weakness with exercise.  He has difficulty swallowing, muscle intention tremors with exertion both in his upper and lower extremities.  He gets better with rest.  He also has a learning disability and seizure like activity when exhausted.  His chromosone abnormality is chromosone 5 31-33.1.  He had syringomyelia but had a subarachnoid shunt installed in 2004.  The doctors seem to think there is a psychological cause.  He chokes on his food at times and his saliva.  I found in a book called diseases of voluntary muscle that one could have SMA without it being in the parents dna. I am still waiting on the results of the blood test for me.  They are doing a cgh test on my son and it showed chromosone 5 and they are fishing with my dna and his.  He also seems to be having Jacksonian seizures.  Is this a possibility?  Thank you again for your help.

[Jordanna Joaquina, MS, CGC]

We are glad that your son is seeing a medical geneticist and encourage you to continue to do so. We do not quite understand the information your provided about your son's chromosome abnormality (5p or 5q?, is there a chromosome deletion?, etc) and whether or not he has a diagnosis of spinal muscular atrophy (SMA).

To give you some information on SMA, the primary cause of SMA is believed to be mutations in a gene called SMN1 at the location 5q13.

Both parents of an affected person are usually carriers (have only one mutation). Two carriers have a 25% chance with each pregnancy to have an affected child, but typically do not have symptoms themselves. Of note, approximately 2% of people affected with SMA have one de novo mutation in the SMN1 gene, meaning that one mutation occurs sporadically, while the other is inherited from a carrier parent.

About 95% of individuals affected with SMA have a deletion in a portion of the SMN1 gene called exon 7 in both copies of the gene. These individuals are said to be homozygous for this deletion. In about 5% of people affected with SMA, only one copy of the SMN1 gene is missing exon 7, and the other copy of the gene has a different type of mutation in the gene. Thus far, researchers have identified nearly 30 such disease-causing mutations.

Extra copies of a gene called SMN2 appear to modify the severity and age of symptom onset of SMA. The SMN2 gene is located adjacent to the SMN1 gene on chromosome 5 at the location q13.

We hope this information is helpful and wish you and your son the best of luck!

[lilviathan]

Thank you for your response.  My son's chromosone is 5q31 - 5q33.1.  This information is very helpful.  Do you think it would be alright if I gave this information to my geneticist?
Thank you very much for this information.