X-linked Ichthyosis Chromosomal Microarray Testing (2015)
FIRST’s MSAB member, Dr. Jennifer Hand of the Mayo Clinic, discusses the process and conclusions of her latest research effort: The phenotype spectrum of X-linked ichthyosis identified by chromosomal microarray.
Is it possible that a milder form of X-linked ichthyosis is more common than we thought?
Chromosomal Microarray (CMA) is usually a blood test that has become a common method to test babies born with multiple birth defects (congenital anomalies) for a genetic, underlying cause. CMA is very effective at screening the whole genome of an individual for chromosome deletions. The question about X-linked ichthyosis arose because most cases of X-linked ichthyosis (over 90%) are caused by a small deletion on the X-chromosome that is spotted easily by routine CMA. Our clinical laboratory at Mayo receives a high volume of infant blood specimen, usually for questions that don’t have anything to do with the skin or ichthyosis. However, the laboratory was recognizing cases with a deletion of the steroid sulfatase gene that causes X-linked ichthyosis, but the referral indications mentioned nothing about the skin. We wondered if it was possible that a case of X-linked ichthyosis could be so mild that a physician wouldn’t even mention it in the reason for testing.
We were able to contact physicians of patients who had a laboratory diagnosis of X-linked ichthyosis for permission to review the medical records more closely. We were a little surprised that none of the patients we reviewed were described as having “polygonal” or “dirty, brown” scale that is typically associated with X-linked ichthyosis. Rather, some were described as having dry skin or eczema and some were not noted to have prominent changes in their skin typically associated with X-linked ichthyosis. Other authors in the past have described that a milder type of X-linked ichthyosis with yellowish, dry scale is possible. We described that in all the cases diagnosed in the laboratory, for whom follow-up was available, and the skin changes were fairly mild.
Our sample size of patients for whom we were able to obtain medical records was small, but in line with the known incidence of X-linked ichthyosis in 1 out of every 1,500 male births. These results don’t show that all cases of X-linked ichthyosis are expected to be mild, but that in cases diagnosed in a laboratory, it is possible that the skin of the affected person will not show prominent “dirty brown” or “polygonal” scale described as typical in the existing literature.