Newborn screening for 3-methylcrotonyl-CoA carboxylase deficiency: population heterogeneity of MCCA and MCCB mutations and impact on risk assessment.
New technology enables expansion of newborn screening (NBS) of inborn errors aimed to prevent adverse outcome. In conditions with a large share of asymptomatic phenotypes, the potential harm created by NBS must carefully be weighed against benefit. Policies vary throughout the United States, Australia, and Europe due to limited data on outcome and treatability of candidate screening conditions. We elaborated the rationale for decision making in 3-methylcrotonyl-coenzyme A (CoA) carboxylase deficiency (MCCD), which afflicts leucine catabolism, with reported outcomes ranging from asymptomatic to death. In Bavaria, we screened 677,852 neonates for 25 conditions, including MCCD, based on elevated concentrations of 3-hydroxyisovalerylcarnitine (3-HIVA-C). Genotypes of MCCA (MCCC1) and MCCB (MCCC2) were assessed in identified newborns, their relatives, and in individuals (n = 17) from other regions, and correlated to biochemical and clinical phenotypes. NBS revealed eight newborns and six relatives with MCCD, suggesting a higher frequency than previously assumed (1:84,700). We found a strikingly heterogeneous spectrum of 22 novel and eight reported mutations. Allelic variants were neither related to biochemical nor anamnestic data of our probands showing all asymptomatic or benign phenotypes. Comparative analysis of case reports with NBS data implied that only few individuals (< 10%) develop symptoms. In addition, none of the symptoms reported so far can clearly be attributed to MCCD. MCCD is a genetic condition with low clinical expressivity and penetrance. It largely represents as nondisease. So far, there are no genetic or biochemical markers that would identify the few individuals potentially at risk for harmful clinical expression. The low ratio of benefit to harm was pivotal to the decision to exclude MCCD from NBS in Germany. MCCD may be regarded as exemplary of the ongoing controversy arising from the inclusion of potentially asymptomatic conditions, which generates a psychological burden for afflicted families and a financial burden for health care systems.
Stadler
Sonja C
SC
Research Center, Department of Biochemical Genetics and Molecular Biology, Dr. von Hauner Children's Hospital, Ludwig-Maximilians-University, Munich, Germany.
Polanetz
Roman
R
Maier
Esther M
EM
Heidenreich
Sylvia C
SC
Niederer
Birgit
B
Mayerhofer
Peter U
PU
Lagler
Florian
F
Koch
Hans-Georg
HG
Santer
René
R
Fletcher
Janice M
JM
Ranieri
Enzo
E
Das
Anibh M
AM
Spiekerkötter
Ute
U
Schwab
Karl O
KO
Pötzsch
Simone
S
Marquardt
Iris
I
Hennermann
Julia B
JB
Knerr
Ina
I
Mercimek-Mahmutoglu
Saadet
S
Kohlschmidt
Nicolai
N
Liebl
Bernhard
B
Fingerhut
Ralph
R
Olgemöller
Bernhard
B
Muntau
Ania C
AC
Roscher
Adelbert A
AA
Röschinger
Wulf
W
D000483:Alleles; D019735:Carbon-Carbon Ligases / Q000172:deficiency* / Q000235:genetics; D015331:Cohort Studies; D003677:Deficiency Diseases / Q000175:diagnosis / Q000235:genetics; D005260:Female; D018740:Genetic Heterogeneity; D005838:Genotype; D005858:Germany; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D009154:Mutation; D015997:Neonatal Screening / Q000331:legislation & jurisprudence*; D019683:Penetrance; D018570:Risk Assessment
D019735:Carbon-Carbon Ligases; C021573:methylcrotonoyl-CoA carboxylase