Chemical pathology analysis of inborn errors of metabolism for expanded newborn screening in Hong Kong

Abstract

Inborn errors of metabolism (IEM) are under international spotlight because of the recent tremendous development in expanded newborn screening (NBS) and molecular genetics. IEM is a difficult subject involving more than 1,000 different disorders with protean clinical presentations and complicated diagnostic pathways. Cumulative incidence of IEM was reported up to 1 in 800. Patients can be affected in any ages. High clinical suspicion alone is not sufficient to reduce morbidities and mortalities. Notably, some IEM are amenable to treatment with promising outcome. Local data regarding the disease spectrum and incidences is largely lacking. Public awareness and readiness for expanded NBS is unknown. This renders difficulties in the consideration of expanded NBS in Hong Kong.

In this study, laboratory data of classical IEM from 2005 to 2009 were retrospectively analyzed (Chapter 2). Local incidence was 1 in 4,122 and that of hyperphenylalaninemias was 1 in 29,542, similar to worldwide figures. Majority (69%) was amino acid disorders, 12% was organic acidemias and 19% was fatty acid oxidation defects. Most of these diseases are effectively amenable to treatment.

Local cases including hyperphenylalaninemia, tyrosinemia type I, arginase deficiency, ornithine transcarbamylase deficiency, very long-chain acyl-CoA dehydrogenase deficiency, tyrosine hydroxylase deficiency, thermolabile carnitine palmitoyltransferase II variants and adults IEM with X-linked adrenoleukodystrophy, cerebrotendinous xanthomatosis, familial transthyretin amyloidosis, Wilson disease and PANK2-associated young-onset Parkinsonism were described (Chapters 1.1.3 and 3).

Electronic chemical pathology consultation service and dried blood spot metabolic screening were implemented (Chapter 4). There were 279 consultations and 158 screening in a 12-month period. Major referral reasons were developmental delay, neurological defects and unexplained biochemical abnormalities. The incidence in high risk screening was 1 in 158. A non-derivatized tandem mass spectrometry assay for amino acids and acylcarnitines was evaluated for its precision, accuracy and reference intervals (Chapter 5). The concordance rate was 100% in inter-laboratory comparison and external quality assurance programs. The method was proven to be accurate, rapid and affordable. It is suitable for large volume testing and emergency diagnostic needs.

A feasibility study of a hospital-based expanded NBS service model was conducted on 360 newborns (Chapter 6). More than 90% of babies were older than 48 hours before discharge and were fit for blood collection. The service model consisted of parent education, consent, postnatal sample collection, technical analysis, clinical interpretation, reporting and follow-up actions.

Questionnaire on the knowledge and attitude towards IEM and expanded NBS was surveyed on 172 parents to investigate the psychological, social and ethical aspects (Chapter 7). Here, 99.4% demanded more education on expanded NBS; 97.6% supported to implement the program; 97.7% supported population screening even though some diseases are incurable. Availability of treatment is not the most important pre-requisite for NBS; 93.9% accepted the possibility of false positive and false negative results. Acceptance towards expanded NBS among parents was high.

Our data indicate that IEM is not uncommon in Hong Kong and it is indisputable for the introduction of a local expanded NBS program. Our data serve as groundwork for policy decision and further discussion on expanded NBS.