PSY31 - COMPARISON OF THE ESTIMATED PREVALENCE OF DIAGNOSED HOMOCYSTINURIA AND PHENYLKETONURIA IN THE UNITED STATES

Abstract

Homocystinuria (HCU) may be underdiagnosed at birth due to inadequately sensitive newborn screening. This study estimated the prevalence of diagnosed HCU in the United States (U.S.) population across age groups, compared with that of diagnosed phenylketonuria (PKU) in similar age groups. In the IBM MarketScan® insurance claims database (MSN) (1/1/2010–12/31/2016), patients with a diagnosis of PKU were identified using standard diagnostic coding systems (ICD-9 270.1 or ICD-10 E70.0), while those with a diagnosis of HCU were identified using solely the more specific ICD-10 code ((E72.11). U.S. census data were used to estimate the age-adjusted national prevalence of diagnosed HCU and PKU patients. Among 97.3 million patients in the MSN, 6,613 (0.068 per 1,000) had a diagnosis of HCU between 1/1/2010 and 12/31/2016, compared to 5,120 (0.053 per 1,000) with a PKU diagnosis. Of the HCU cases, 0.51% were ages 0–11 years and 80% were 45 years or older at the time of the first recorded diagnosis during the study period. For PKU cases, 53% were ages 0–11 years and 13% were 45 years or older. The estimated age-adjusted prevalence of diagnosed HCU in the US for 2017 was ∼0.01% (31,162 cases) vs. 0.005% (16,615 cases) for PKU. As expected, the highest proportion of diagnosed PKU was observed in the youngest age group (ages 0–11 years), likely due to infants being diagnosed through mandatory newborn screening. Conversely, the proportion of diagnosed HCU cases in the younger age group was approximately ten times smaller, implying that HCU patients are not diagnosed primarily at birth or during early childhood. This suggests that current newborn screening tests fail to capture the vast majority of HCU cases, with patients diagnosed at later ages, even into adulthood, when they present with symptoms or comorbid conditions indicative of HCU.