Most common metabolic disorders in childhood. Neonatal screening and diagnostic approach to the. Inborn errors of metabolism (IEM)

Transcription

1 Department of Pediatrics and Developmental Disorders Medical University of Bialystok Most common metabolic disorders in childhood. Neonatal screening and diagnostic approach to the inborn errors of metabolism (IEM). Pawel Abramowicz M.D., Ph.D. Jerzy Konstantynowicz MD, PhD, Assoc. Prof. Inborn errors of metabolism (IEM) a large class of genetic diseases involving disorders of metabolism. Normal metabolism A B C D 1

2 Inborn error of metabolism Defect of single gene that code for enzyme that facilitate conversion of one substance A (substrate) into the other B (product). AA A B C D Inborn error of metabolism Problems arise due to accumulation of substance (A) or its alternative metabolites (C and D) which are toxic or interfere with normal function. A A AA B C CC D Inborn error of metabolism Problems arise due to accumulation of substance (A) or its alternative metabolites (C and D) which are toxic or interfere with normal function. AA AA A AA B CC CC C CC DD DD D DD Storage of metabolites proximally to metabolic block and alternative metabolic pathways (toxic products) 2

3 IEM - prevalence Over 1000 IEM were described until now. IEM belong to the group of rare diseases (< 1:2000). Particular diseases are very rare but altogether they are frequent. phenylketonuria (PKU) 1: 7000 galactosemia 1: propionic aciduria (PA) 1: maple syrup urine disease (MSUD) 1: lysosomal storage diseases 1: IEM - prevalence Over 1000 IEM were described until now. IEM belong to the Remember: group of rare diseases (< 1:2000). Particular diseases are very rare but altogether they Rare frequent. diseases phenylketonuria paradoxically (PKU) 1: 7000are common galactosemia 1: propionic aciduria (PA) 1: maple syrup urine disease (MSUD) 1: lysosomal storage diseases 1:

4 IEM - inheritance All inheritance patterns are possible. The most common are autosomal recessive inheritance - 25% high risk of sick child delivered from each pregnancy Definitely more common in the families where parents are related to each other. The importance of genetical counselling 60% of IEM begins during neonatal period but 40% may begin on each age. In neonates the symptoms of IEM develop very rapidly but are very non-characteristic and can incorrectly suggest: Neonatal sepsis Respiratory distress syndrome (RDS) Perinatal injury (bleeding to CNS) Intestinal obstruction Endocrine disorders (Congenital adrenal hyperplasia, CAH) Congenital heart defect There is no single, isolated sign or symptom which could allow to diagnose (or exclude) congenital metabolic disorder 4

5 nylketonuria (PKU) One of the most frequent metabolic disorder associated with aminoacid enzymatic disturbance Caused by inborn deficit of phenyloalanine hydroxylase (PAH) Autosomal recesive Incidence in Poland 1:7000 of newborns Ivar Asbjørn Følling ( ) Norwegian physician and biochemist Følling test - FeCl discovery of phenylketonuria (PKU) Følling disease He was the first who associated IEM with intelectual disability The essence of metabolic changes in PKU The accumulation of phenylalanine () which is transaminated to phenylpyruvate. Both, and phenylpyruvate are very toxic with a predilection to the central nervous system. 5

6 nylketonuria (PKU) Child looks normally at birth If left untreated PKU leads to: Severe brain damage and intellectual disability Seizures Spasticity Albinism (fair skin and hair) Musty odor, mouse s urine odor Microcephaly Fail to attain early developmental milestones Eczema Behavioural disorders Untreated patient with classic PKU One of the most severe intellectual disability IQ level % were not able to talk 35% were not able to walk PKU treatment -restricted diet is the only and fully effective treatment option 6

7 -restricted diet Diet for life Eliminate foods rich in : meat, chicken, fish, eggs, nuts, cheese, milk and other dairy products. Foods like potatoes, bread, pasta and corn must be monitored. Breastfeeding may be continued but the quantity must be monitored. Protein intake is supplied by special milkformulas (PKU-formulas), enriched in tyrosine which is normally derived from and other nutrients. Dietary treatment of PKU require frequent monitoring Target serum levels Age Desirable concentration 0 5 yrs 2 4 mg /dl 6 14 yrs 2 8 mg /dl > 14 yrs <12 mg /dl Prognosis Normal development and intelligence providing that an immediate and efficient dietary treatment was started. 7

8 Maternal PKU Disease of the mother The symptoms developed by healthy fetus Teratogenic influence of on fetal growth Microcephaly % Growth retardation 90 % Intrauterine hypotrophy 40 % Congenital heart defects 14 % Dysmorphic features Other organs defects The odds for having a healthy child by woman with PKU is the same as in general population (healhy woman) if only level before and throughout the whole pregnancy was between 2 and 6 mg/dl. 8

9 Congenital hypothyroidism (CH) Deficit of thyroid hormones Impaired brain development mental retardation Congenital hypothyroidism is the most common preventable cause of intellectual disability. Causes: congenital abnormalities (aplasia, hypoplasia ectopic thyroid gland, disturbed hormone secretion /syntheisis/) Incidence 1:4000 May be transient or permanent Congenital hypothyroidism (CH) Newborns looks healthy (normal birth weight and height) Symptoms are non characteristic during the first weeks of life: Drowsiness, excessive sleeping Decreased muscle tone Low and hoarse cry Feeding difficulties Constipation Enlarged tongue (macroglossia) Large anteriol fontanelle Umbilical hernia Dry, mottled skin Decreased body temerature Jaundice If left untreated leads to a severe and permanent intellectual impairment (IQ < 80) Congenital hypothyroidism (CH) Treatment consists of a daily dose of thyroxine. Prognosis: patients correctly treated with thyroxine grow and develop normally 9

10 Cystic fibrosis (CF) - mucoviscidosis Most common genetic disorder of the white race Incidence (Poland) 1:2300 Inheritance: autosomal recessive CFTR gene chloride channel abnormal transport of Na and Cl across the epithelium Production of thick, viscous secretions in the respiratory and digestive system (exocrinopathy) Affects mostly the lungs but also the pancreas, liver and intestine. Neonatal screening Largely available populational tests used for the early identification of individuals with congenital disorders The rationale for neonatal screening Important part of preventive medicine. To diagnose the disease before developing of the symptoms and irreversible damages. An early (presymptomatic) treatment may protect the child from the mental impairment, death or at least could alleviate the course of the disease. 10

11 Characteristics of metabolic screening tests Safe, sensitive, specific, largely accepted, simple, available, relatively not expensive A well-organized system for taking blood/urine samples and feasibility of delivering to the laboratory High quality performance, diagnostics and surveillance on high risk children Availability of treatment facilities and post-screening care The screening programm consist of 3 steps 1. Screening test 2. Diagnostic tests to confirm (or exclude) diagnosis 3. Early treatment Robert Guthrie ( ) Microbiological test for PKU Bacillus subtillis growth was restored in the presence of phenyloalanine metabolites from PKU-patients 11

12 Populational screening Neonatal heel prick Neonatal screening in Poland MS/MS (AA+AC+OA) Classic tests Other PKU (1964) CH (1983) CF (1999) Congenital deafness Tandem Mass Spectometry MS/MS PKU (colorimetry) CH CF MS/MS (Nov %) PKU (colorimetry) CH CF 20 inborn metabolic errors Organic aciduria (OA) Fatty acid oxidation disorders (FAO) Aminoacidopathies (AA) Not screened Galactosemia (GALT) Biotynidase deficit (BIOT) Congenital adrenal hyperplasia (CAH) Neonatal screening in Poland MS/MS (AA+AC+OA) Classic tests Other PKU (1964) CH (1983) CF (1999) Congenital deafness Tandem Mass PKU In 2015 Spectometry congenital(colori- metry) adrenal CH hyperplasia CF MS/MS has been is included to neonatal screening program in Poland MS/MS (Nov %) 20 inborn metabolic errors PKU (colorimetry) CH CF Organic aciduria (OA) Fatty acid oxidation disorders (FAO) Aminoacidopathies (AA) Not screened Galactosemia (GALT) Biotynidase deficit (BIOT) Congenital adrenal hyperplasia (CAH) 12

13 Dried blood spot testing Specially designed filter paper (collection card) The neonatal heel prick It consists of making a pinprick puncture in a heel of the newborn and soaking the blood into the collection card Dried blood spot testing Blood samples are blotted and dried on a specially designed filter paper 13

14 How do we screen? nylketonuria Testing for raised concentration of phenylalanine in dried blood spot. Normal range: < 2.5(3) mg/dl Congenital hypothyroidism How do we screen? TSH (thyroid stimulating hormone) measurement in dried blood spot (heel prick). Normal range: < 15 miu/l The goal of newborn screening for CH is to detect and start treatment within the first 2 weeks of life. Cystic fibrosis (CF) - mucoviscidosis How do we screen? Testing for raised concentration of IRT (immunoreactive trypsinogen) in dried blood spot. if possitive (>99.4 th percentile): sweat-testtest (measures the concentration of chloride that is excreted in sweat) and DNA analysis for identification of mutations in the CFTR gene. 14

15 It is recommended that the screening test be performed when the infant is between 48 and 72 hours of age to avoid false positive and false negative results. Over 20 other (less common) inborn errors of metabolism are detected with the use of Tandem Mass Spectrometry method. nylketonuria Tandem Mass Spectrometry (MS/MS) MSUD maple syrup urine disease 15

16 Percentage newborns screened >90% 50-90% 20-50% 10-20% <10% Take home messages All neonates have to be screened within the first days of life. Currently, over 20 inborn errors of metabolism are detected in the simple dried blood test. An early diagnosis and treatment protect the child from irreversible (brain) damages. Thank you 16