A-348 Portable aptamer-based home monitoring system for blood phenylalanine measurement
Authors: Boyce-Jacino M , Das K 
Published: October 2024

Abstract

Background
Aptatek BioSciences, Inc. has developed a home monitoring tool for blood phenylalanine (phe) levels. The Aptatek system integrates a proprietary aptamer assay approach with a user-friendly handheld, smartphone-enabled test platform. PKU (phenylketonuria), is an inborn error of phenylalanine (Phe) metabolism If undiagnosed or untreated, phe accumulates in all body tissues, including the blood and brain, where it is especially neurotoxic and when untreated it can cause significant cognitive impairment and neurological defects.
PKU management targets maintaining blood Phe concentration within the therapeutic range (120-360uM) to avoid severe neurological sequelae, mainly through nutritional therapy.

Methods
PheCheck™ includes a portable hand-held reader, software accessible as a mobile phone application, and a disposable single-use lateral flow cassette, blood collection, cap, and buffer chamber. PheCheck™ detects phe by binding of the phe in a small blood sample using small molecule-specific DNA aptamers. A patient (or caregiver) collects 5μl of capillary blood using a lancet to lance the fingertip and use the collection cap to collect the specimen. Once collected, the specimen is placed into the buffer chamber where the blood is diluted and processed in preparation for a lateral flow assay. The buffer chamber is placed on top of a lateral flow cassette to release the solution into the cassette. The lateral flow cassette is inserted into a small electronic reader after specimen incubation. The reader will detect a fluorescent signal from the strip and report the quantitative Phe concentration present in the specimen to the integrated mobile phone application. The reader has a simple design with a single operating push button, USB data connection port, and replaceable battery compartment. The reader reads the output of the lateral flow cassette and reports the result to a Smartphone app. The app is designed to either display the quantitative results or store the results without displaying the quantitative value.

Results
Twelve patients were trained on the PheCheck system and observed using the system for self-testing. Patients also prepared dried blood spot cards for comparative testing using LC-mass spectrometry. Patients were asked to return to the clinic within two weeks to retest. The blood phenylalanine levels measured by the PheCheck system were within targeted standard deviation of the dried blood spots demonstrating the feasibility of portable home-based testing for routine monitoring of blood phenylalanine levels in phenylketonuria patients. Such a portable system would enable real time monitoring and adjustment of diet or therapy for chronic diseases such as PKU.

Conclusions
Aptatek has developed a DNA aptamer based portable monitor for measuring blood phenylalanine levels. The system quantitatively measures phenylalanine from a 5-microliter finger stick blood sampler. Aptamer-based detection of phenylalanine provides reliable quantitation across a wide clinical concentration range and encouraging performance relative to gold standard testing of venous blood draw or dried blood spots. Analysis of samples from patients on Palynziq indicate that the PheCheck system could provide more reliable testing than venous blood draws. The system shows strong promise for routine home monitoring of blood phe levels by patients.