Diagnosis, genetic characterization and clinical follow up of mitochondrial fatty acid oxidation disorders in the new era of expanded newborn screening: A single centre experience

Introduction

Mitochondrial fatty acid oxidation disorders (FAODs) are a heterogeneous group of hereditary autosomal recessive diseases included in newborn screening (NBS) program in Italy. The aim of this study was to analyse FAODs cases, identified either clinically or by NBS,for clinical and genetic characterization and to evaluate a five years' experience of NBS, in the attempt to figure out the complexity of genotype-phenotype correlation and to confirm the clinical impact of NBS in our centre experience.

Materials and methods

We analysed FAODs patients diagnosed either by NBS or clinically, followed since February 2014 to April 2019 at the Regional Screening Centre and Inherited Metabolic Diseases Unit of Verona. Diagnosis was confirmed by plasma acylcarnitines, urinary organic acids, enzymatic and genetic testing. For not clear genotypes due to the presence of variants of uncertain significance, in silico predictive tools have been used as well as enzymatic activity assays. Patients underwent clinical, nutritional and biochemical follow up.

Results

We diagnosed 30 patients with FAODs. 20 by NBS: 3 CUD, 6 SCADD, 5 MCADD, 4 VLCADD, 2 MADD. Overall incidence of FAODs diagnosed by NBS was 1:4316 newborns. No one reported complications during the follow up period. 10 patients were diagnosed clinically: 2 CUD, 2 CPT2D, 1 VLCADD, 5 MADD. Mean age at diagnosis was 29.3 years. Within this group, complications or symptoms were reported at diagnosis, but not during follow-up. 12 mutations not previously reported in literature were found, all predicted as pathogenic or likely pathogenic.

Discussion and conclusions

Our study highlighted the great phenotypic variability and molecular heterogeneity of FAODs and confirmed the importance of a tailored follow up and treatment. Despite the short duration of follow up, early identification by NBS prevented diseases related complications and resulted in normal growth and psycho-motor development as well.

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Early identification by newborn screening prevents disease related complications.

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Newborn screening is changing prevalence clinical and molecular heterogeneity of FAODs.

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Genotype-phenotype correlation helps to achieve personalized follow-up and treatment.

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Enzymatic assay may be pivotal in predicting phenotype and symptoms severity.

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Diagnosis on clinical grounds is anyway important to change disease course.

Rapid method towards proteomic analysis of dried blood spots by MALDI mass spectrometry

Neonatal dried blood spots (DBS) are routinely utilized in the clinical setting as a diagnostic tool for various genetic disorders and infectious diseases. DBS allow for minimally invasive, small volume blood collection and are stored at room temperature. Neonatal whole blood and serum samples can be important in determining genetic risk factors and predicting infantile disease; however, at the present time, limited methods exist for rapidly analyzing DBS samples for their proteomic profile, years after samples have been collected. A novel method is presented for the extraction and analysis of target proteins and peptides from neonatal DBS using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Extraction parameters were optimized to achieve ideal signal intensity and resolution to obtain protein identifications. Samples were extracted from filter paper with 0.1% TFA in H₂O for 72 h. The extract was subjected to enzymatic digestion, spotted on an ITO-coated glass slide, and washed in order to remove salts. Analysis of extracted blood spots from ten newborns was completed. Similarities and differences in the proteomic profile of the washed extracts are presented, herein, to verify the viability of this method for analysis of dated DBS samples. This method allows for analysis of DBS samples years after collection and can be utilized to correlate diseases or disorders manifesting later in life with potential risk factors presenting in the proteomic profile of the DBS collected at time of birth.

High incidence of low vitamin B12 levels in Estonian newborns

Vitamin B12 deficiency seems to be more common worldwide than previously thought. However, only a few reports based on data from newborn screening (NBS) programs have drawn attention to that subject. In Estonia, over the past three years, we have diagnosed 14 newborns with congenital acquired vitamin B12 deficiency. Therefore, the incidence of that condition is 33.8/100,000 live births, which is considerably more than previously believed. None of the newborns had any clinical symptoms associated with vitamin B12 deficiency before the treatment, and all biochemical markers normalized after treatment, which strongly supports the presence of treatable congenital deficiency of vitamin B12. During the screening period, we began using actively ratios of some metabolites like propionylcarnitine (C3) to acetylcarnitine (C2) and C3 to palmitoylcarnitine (C16) to improve the identification of newborns with acquired vitamin B12 deficiency. In the light of the results obtained, we will continue to screen the congenital acquired vitamin B12 deficiency among our NBS program. Every child with aberrant C3, C3/C2 and C3/C16 will be thoroughly examined to exclude acquired vitamin B12 deficiency, which can easily be corrected in most cases.

Application of a diagnostic methodology by quantification of 26:0 lysophosphatidylcholine in dried blood spots for Japanese newborn screening of X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is a rare inherited metabolic disease that results in the accumulation of very long chain fatty acids (VLCFA) in plasma and all tissues. Recent studies regarding cerebral X-ALD (CALD) treatment emphasize the importance of its early diagnosis. 26:0 lysophosphatidylcholine (LysoPC) is a sensitive biomarker for newborn screening of X-ALD, while its application for Japanese DBS is unclear. Therefore, we evaluated the feasibility of 20:0 LysoPC and 24:0 LysoPC along with 26:0 LysoPC for diagnosing X-ALD in a cohort of newborns (n = 604), healthy adults (n = 50) and patients (n = 4). Results indicated that 26:0 LysoPC had strong significance for discrimination of patients by the amounts of 2.0 to 4.0 and 0.1 to 1.9 pmol/punch for patients and newborns/healthy adults, respectively. Based on these values, we recommend that further diagnostic confirmation is essential if the amount of 26:0 LysoPC in DBS is above 1.7 pmol/punch.

Retrospective TREC testing of newborns with Severe Combined Immunodeficiency and other primary immunodeficiency diseases

In Manitoba, Canada, the overall incidence of Severe Combined Immunodeficiency (SCID) is three-fold higher than the national average, with SCID overrepresented in two population groups: Mennonites and First Nations of Northern Cree ancestries. T-cell receptor excision circle (TREC) assay is being used increasingly for neonatal screening for SCID in North America. However, the majority of SCID patients in Manitoba are T-cell-positive. Therefore it is likely that the TREC assay will not identify these infants. The goal of this study was to blindly and retrospectively perform TREC analysis in confirmed SCID patients using archived Guthrie cards. Thirteen SCID patients were tested: 5 T-negative SCID (3 with adenosine deaminase deficiency, 1 with CD3δ deficiency, and 1 unclassified) and 8 T-positive SCID (5 with zeta chain-associated protein kinase (ZAP70) deficiency and 3 with inhibitor of kappa light polypeptide gene enhancer in B-cells, kinase beta (IKKβ) deficiency). As a non-SCID patient group, 5 Primary Immunodeficiency Disease (PID) patients were studied: 1 T-negative PID (cartilage-hair hypoplasia) and 4 T-positive PID (2 common immune deficiency (CID), 1 Wiskott–Aldrich syndrome, and 1 X-linked lymphoproliferative disease). Both patient groups required hematopoietic stem cell transplantation. In addition, randomly-selected de-identified controls (n = 982) were tested. Results: all T-negative SCID and PID had zero TRECs. Low-TRECs were identified in 2 ZAP70 siblings, 1 CID patient as well as 5 preterm, 1 twin, and 4 de-identified controls. Conclusions: TREC method will identify T-negative SCID and T-negative PID. To identify other SCID babies, newborn screening in Manitoba must include supplemental targeted screening for ethnic-specific mutations.