Association of Mutations in SCO2, a Cytochrome C Oxidase Assembly Gene, with Early Fetal Lethality

OBSERVATION Association of Mutations in SCO2, a Cytochrome c Oxidase Assembly Gene, With Early Fetal Lethality

Stacey K. H. Tay, MBBS; Sara Shanske, PhD; Paige Kaplan, MBBCh; Salvatore DiMauro, MD

Background: SCO2 is a cytochrome c oxidase (COX) Main Outcome Measures: Mutations in the abortus assembly gene that encodes a mitochondrial inner mem- by sequencing the SCO2 gene and confirmation of the brane protein that probably functions as a copper trans- point mutations as determined by restriction fragment porter. Mutations in SCO2 have been associated with se- length polymorphism analysis. vere COX deficiency and early-onset fatal infantile hypertrophic cardiomyopathy, encephalopathy, and neu- Results: As in the previous affected child, we found a rogenic muscle atrophy. Fetal wastage has not been de- missense mutation (E140K) and a nonsense mutation scribed in association with mutations of SCO2. (Q53X) in the abortus.

Objective: To investigate a case of early spontaneous Conclusions: The typical clinical presentation of SCO2 abortion in a family carrying mutations in SCO2. mutations is severe, rapidly progressive hypertrophic Design: Case report. cardiomyopathy that presents in the neonatal period and is often associated with respiratory difficulties, Patients: Spontaneous abortion in the first trimester oc- metabolic acidosis, and hypotonia. The experience in curred in a woman whose first pregnancy had also re- this family suggests that mutations in SCO2 may also be sulted in a miscarriage in the first trimester and whose associated with early spontaneous abortions and fetal only child had died at 53 days of life from cardioencepha- wastage. lomyopathy. This child was a compound heterozygote for mutations in SCO2, and her parents were heterozygous for each mutation. Arch Neurol. 2004;61:950-952

YTOCHROME C OXIDASE copper-zinc superoxide dismutase, also de- (COX), the terminal en- velop cardiac hypertrophy.14 zyme complex of the SCO2 is a nuclear gene, inheritance of mitochondrial electron SCO2 deficiency is autosomal recessive, and transport chain, transfers allpatientshaveacommonG1541A(E140K) electronsC from cytochrome c to molecular mutation on 1 allele.8 Homozygous G1541A oxygen and pumps protons across the in- mutations have been found in patients with ner mitochondrial membrane.1 COX defi- a milder phenotype, consisting of delayed ciency is one of the most frequent mito- developmentofhypertrophicobstructivecar- chondrial abnormalities in patients who diomyopathyandsevereneuromusculardis- present with Leigh syndrome.2 Molecular ease.15 Fetal wastage has not been associated defects of 5 nuclear COX assembly genes, withmutationsofSCO2.Herein,wedescribe SURF 1,3-5 SCO2,6-8 SCO1,9 COX 10,10 and early spontaneous abortions in a family with COX 15,11 have been identified in patients mutations of SCO2. with Leigh syndrome and COX deficiency. SCO2 encodes a 266–amino acid pro- METHODS From the Department of tein that is imported into mitochondria and Neurology, Columbia is required for the correct assembly of cop- REPORT OF A CASE University College of per into the holoenzyme.12,13 Functional im- Physicians and Surgeons, pairment of the SCO2 protein results in a The first pregnancy in this family resulted in a New York, NY (Drs Tay, decrease of copper transport or delivery to first-trimester, spontaneous abortion at 11 weeks. Shanske, and DiMauro); and COX subunits I and II and decreased cata- The offspring of the second pregnancy (II-2) Section of Metabolic Diseases, (Figure 1) was patient 3 in the original pub- Children’s Hospital of lytic function. Mutations in SCO2 have been lication,6 which described SCO2 mutations in Philadelphia, Philadelphia, Pa described in patients with fatal infantile car- fatal infantile cardioencephalomyopathy with 6-8 (Dr Kaplan). The authors have dioencephalomyopathy. Copper- COX deficiency. The third pregnancy resulted no relevant financial interest in deficient rats with low cuproenzyme lev- in another spontaneous abortion in the first tri- this article. els, including lysyl oxidase, COX, and mester at 10 weeks.

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©2004 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/27/2021 The affected child (II-2) was a full-term, 3460-g product of normal pregnancy and delivery. She was mildly hypotonic at birth and at 15 hours was noted to have a cardiac murmur. She devel- oped respiratory distress and required assisted ventilation. She I-1 I-2 had lactic acidosis, and a 2-dimensional echocardiogram showed a severely thickened left ventricle with no evidence of outflow tract obstruction. A magnetic resonance image of the brain was normal. By 42 days of life, a subsequent 2-dimensional echocardiogram showed more severe cardiac hypertrophy and oblitera- tion of the left ventricular cavity during systole. After ventilatory II-1II-2 II-3 support was withdrawn, she died at 53 days of life. Autopsy showed a grossly enlarged globular heart, a mildly enlarged and congested liver, and cerebral atrophy. The car- Figure 1. Pedigree diagram. The square indicates mole; circles, females; diac left ventricle and septum were markedly hypertrophic. The fully shaded symbol, patient; and partially shaded symbols, unaffected cerebral hemispheres showed an abnormal gyral pattern. heterozygotes. Small black circles represent spontaneous abortions. Microscopic examination of the heart showed myocardial fiber disarray and occasional myocyte hypertrophy. Skeletal muscle A showed rounded myocytes with increased variation of fiber size. Q53X Brain histologic analysis showed cerebral white matter gliosis with Pro Gly Gln Pro Gln Gly focal white matter necrosis and petechial hemorrhages, focal cor- Stop tical dysplasia of the left temporal lobe, and mild cortical and hip- pocampal neuronal dropout. The cerebellum had focal heteroto- C C A G G G C C C T N G G G C T G G C C C pia and collections of granular cell neurons in the dentate nucleus. G 100 A 110 The spinal cord showed mild gliosis and white matter spongiosis. COX activity was decreased in postmortem tissues (data published previously),6 especially in cardiac muscle, where it was 8% of control. The child was a compound heterozygote of the Q53X nonsense mutation (C1280T) and the E140K missense mutation (G1541A). The father (I-1) was heterozygous for the Q53X mutation and the mother (I-2) was heterozygous for the E140K mutation. For the third pregnancy, prenatal diagnosis was sought, but spontaneous abortion occurred before the prenatal testing could occur. There were no other complications in any of the pregnancies, such as uterine abnormalities, endocrine or im- B munological dysfunction, or infections that could have led to E140K the previous spontaneous abortions (II-1 and II-3). Glu Leu Glu Asp Pro Cys Lys SCREENING FOR MUTATIONS IN SCO2 T T C T C C A G C T N G T C T G G G C A G The DNA was extracted by a standard protocol from blood of C the parents, autopsy tissues of II-2, and the product of concep- 190 T 200 tion II-3.16 The SCO2 gene was amplified and directly se- quenced as described previously.6

RESTRICTION FRAGMENT LENGTH POLYMORPHISM ANALYSIS Restriction fragment length polymorphism analysis of the E140K and the Q53X mutations was performed as described.6

RESULTS

Sequencing of the SCO2 gene in the DNA extracted from Figure 2. Electropherograms of the antisense strands of the DNA of II-3 tissue of the abortus revealed the E140K (G1541A) mu- showing (A) the Q53X (C1280T) and (B) the E140K (G1541A) mutations. The deduced amino acid sequence for the wild-type allele is shown. The arrows tation and the Q53X (C1280T) mutation (Figure 2). indicate nucleotide (N) changes in each strand. There isaGtoAtransition in Restriction fragment length polymorphism analysis simi- the Q53X mutation, and C to T transition in the E140K mutation. Pro larly confirmed that II-3 was a compound heterozygote indicates proline; Gly, glycine; Gln, glutamine; Glu, glutamic acid; Leu, with the E140K and Q53X mutations. leucine; Asp, aspartic acid; Cys, cysteine, and Lys, lysine.

15 8 COMMENT ity in the tissues tested (Table). Jaksch et al described a family in which the 2 affected siblings were com- The typical clinical presentation of SCO2 mutations is pound heterozygotes. Their mother had 2 miscarriages severe, rapidly progressive hypertrophic cardiomyop- in the 11th and 12th weeks of pregnancy. athy in the neonatal period, often associated with respi- It is not surprising that both families in whom recur- ratory difficulties, metabolic acidosis, and hypotonia. Ho- rent abortions were reported harbored heterozygous mu- mozygosity of the E140K mutation has been associated tations, because the phenotype in compound heterozy- with later onset, longer survival, and higher COX activ- gotes is more severe than that of E140K homozygotes, who

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Mutations Onset Death, mo COX Residual Activity, % Reference Compound Heterozygotes E140K/Q53X* Neonatal 2 18 6 E140K/Q53X† Antenatal First-trimester abortion Not performed E140K/Q53X 6 wk 3 4 6 E140K/S225F 10 wk 6 4 6 E140K/R90X 3 wk 1 10 8 E140K/R90X 3 wk 1 12 8 E140K/R173W 8 wk 4 0 8 E140K/L151P Neonatal 3 7 17 E140K/I63fs 4 wk 2 6 18 Homozygotes E140K/E140K 8 mo 13 30 15 E140K/E140K 17 mo Alive at 24 mo 16 15 E140K/E140K 8 mo 8 Not performed 15

Abbreviations: COX, cytochrome c oxidase. *Patient II-2 in the pedigree described. †Abortus II-3 in the pedigree described.

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