San Diego-based Sequenom Inc. is preparing to respond this week to a letter from the federal Food and Drug Administration that may impact tests that are processed in Grand Rapids.

The company was one of 15 nationwide to receive similar letters from the FDA, including Interleukin Genetics Inc., a Massachusetts company with close ties to Ada direct sales company Amway.

Sequenom spokesman Ian Clements said the letter appears to be connected to an evolving FDA crackdown on genetic tests marketed directly to consumers. The FDA recently conducted a two-day public meeting and testified to Congress regarding laboratory developed tests.

Clements said the letter caused some confusion at Sequenom, as it appears to refer to a test for Down syndrome that is under development and not on the market.

Sequenom prenatal tests that are on the market and being processed at the Sequenom Center for Molecular Medicine — a CLIA-certified laboratory in the Cook-DeVos Center for Health Sciences in Grand Rapids — include fetal Rhesus D genotyping, fetal sex determination and screening parents for cystic fibrosis carriers.

The company is in the process of clinical testing for a new version of a prenatal maternal blood test for Down syndrome. Also in Sequenom’s pipeline is a test for predisposition to macular degeneration, an eye disorder that can cause blindness.

SensiGene Fetal Rhesus D Genotyping and the fetal sex determination test analyze fetal DNA material in the mother’s blood using Sequenom’s licensed SEQureDx technology. But gender would not fall under the FDA letter’s reference to genetic or chromosomal abnormality, Clements said.

“As we analyzed it, we came to the conclusion that we believe that they can only be referring to the Rhesus D genotyping test,” Clements said. “It’s our belief that this test falls into the category of lab developed test, or LDT. That’s going to be our position, I think, as we look to respond to the FDA.”

If it were considered a medical device, it would come under stringent FDA regulations, he said.

Clements said the FDA gave the company 15 days to respond to the July 19 letter.

Sequenom’s previous version of the Down syndrome test was discredited when the former head of research pleaded guilty to lying about its effectiveness to investors.

The company had been planning a major expansion of the lab in Grand Rapids, hiring as many as 500 employees. Clemens said the change in Sequenom’s Down syndrome test has prompted executives to decide to process them at its San Diego lab.

In an SEC filing, Interleukin Genetics said it had received an FDA letter regarding its Inherent Health tests, which provide genetic analysis for weight management, nutritional needs, heart and bone health, and the risk for severe periodontal disease. The company said it believes the tests do not fall under the definition of medical devices and intends to respond to the FDA with those comments.

Interleukin Genetics also posted a statement indicating that is in danger of being de-listed from the NYSE Amex LLC exchange because stockholder equity is below $6 million and losses on continuing operations or net losses have occurred in each of the past five years. The company stated that it intends to request a hearing before the exchange’s Listing Qualifications Panel.

Interleukin’s seven-member board of directors includes four people with positions at Amway or its subsidiary Access Business Group, as well as a former executive of X-Rite Inc.

In testifying to Congress July 22, Dr. Jeffrey Shuren, director of the FDA’s Center for Devices and Radiological Health, said that the FDA has held the authority for more stringent regulations on LDTs since 1976, but until now chose not to exercise it. But several factors have prompted the FDA to develop LDT regulations based on three risk levels, Shuren said. Several studies have recommended closer scrutiny of the industry, and since the completion of the Human Genome Project in 2003, genetic tests have been developed that are far more complex and riskier for treatment than anything preceding them.

The direct-to-consumer Web-based marketing of 23andme.com and Pathway Genomics’ plan to sell a genetic testing kit in 6,000 Walgreens stores also concerned the FDA, he said.