Deficiency of the alpha and beta subunits of pyruvate dehydrogenase in a patient with lactic acidosis and unexpected sudden death

New findings in a global approach to dissect the whole phenotype of PLA2G6 gene mutations

Mutations in PLA2G6 gene have variable phenotypic outcome including infantile neuroaxonal dystrophy, atypical neuroaxonal dystrophy, idiopathic neurodegeneration with brain iron accumulation and Karak syndrome. The cause of this phenotypic variation is so far unknown which impairs both genetic diagnosis and appropriate family counseling. We report detailed clinical, electrophysiological, neuroimaging, histologic, biochemical and genetic characterization of 11 patients, from 6 consanguineous families, who were followed for a period of up to 17 years. Cerebellar atrophy was constant and the earliest feature of the disease preceding brain iron accumulation, leading to the provisional diagnosis of a recessive progressive ataxia in these patients. Ultrastructural characterization of patients’ muscle biopsies revealed focal accumulation of granular and membranous material possibly resulting from defective membrane homeostasis caused by disrupted PLA2G6 function. Enzyme studies in one of these muscle biopsies provided evidence for a relatively low mitochondrial content, which is compatible with the structural mitochondrial alterations seen by electron microscopy. Genetic characterization of 11 patients led to the identification of six underlying PLA2G6 gene mutations, five of which are novel. Importantly, by combining clinical and genetic data we have observed that while the phenotype of neurodegeneration associated with PLA2G6 mutations is variable in this cohort of patients belonging to the same ethnic background, it is partially influenced by the genotype, considering the age at onset and the functional disability criteria. Molecular testing for PLA2G6 mutations is, therefore, indicated in childhood-onset ataxia syndromes, if neuroimaging shows cerebellar atrophy with or without evidence of iron accumulation.

The spectrum of pyruvate dehydrogenase complex deficiency: clinical, biochemical and genetic features in 371 patients

CONTEXT

Pyruvate dehydrogenase complex (PDC) deficiency is a genetic mitochondrial disorder commonly associated with lactic acidosis, progressive neurological and neuromuscular degeneration and, usually, death during childhood. There has been no recent comprehensive analysis of the natural history and clinical course of this disease.

OBJECTIVE

We reviewed 371 cases of PDC deficiency, published between 1970 and 2010, that involved defects in subunits E1α and E1β and components E1, E2, E3 and the E3 binding protein of the complex.

DATA SOURCES AND EXTRACTION

English language peer-reviewed publications were identified, primarily by using PubMed and Google Scholar search engines.

RESULTS

Neurodevelopmental delay and hypotonia were the commonest clinical signs of PDC deficiency. Structural brain abnormalities frequently included ventriculomegaly, dysgenesis of the corpus callosum and neuroimaging findings typical of Leigh syndrome. Neither gender nor any clinical or neuroimaging feature differentiated the various biochemical etiologies of the disease. Patients who died were younger, presented clinically earlier and had higher blood lactate levels and lower residual enzyme activities than subjects who were still alive at the time of reporting. Survival bore no relationship to the underlying biochemical or genetic abnormality or to gender.

CONCLUSIONS

Although the clinical spectrum of PDC deficiency is broad, the dominant clinical phenotype includes presentation during the first year of life; neurological and neuromuscular degeneration; structural lesions revealed by neuroimaging; lactic acidosis and a blood lactate:pyruvate ratio ≤ 20.

The spectrum of pyruvate dehydrogenase complex deficiency: clinical, biochemical and genetic features in 371 patients

CONTEXT

Pyruvate dehydrogenase complex (PDC) deficiency is a genetic mitochondrial disorder commonly associated with lactic acidosis, progressive neurological and neuromuscular degeneration and, usually, death during childhood. There has been no recent comprehensive analysis of the natural history and clinical course of this disease.

OBJECTIVE

We reviewed 371 cases of PDC deficiency, published between 1970 and 2010, that involved defects in subunits E1α and E1β and components E1, E2, E3 and the E3 binding protein of the complex.

DATA SOURCES AND EXTRACTION

English language peer-reviewed publications were identified, primarily by using PubMed and Google Scholar search engines.

RESULTS

Neurodevelopmental delay and hypotonia were the commonest clinical signs of PDC deficiency. Structural brain abnormalities frequently included ventriculomegaly, dysgenesis of the corpus callosum and neuroimaging findings typical of Leigh syndrome. Neither gender nor any clinical or neuroimaging feature differentiated the various biochemical etiologies of the disease. Patients who died were younger, presented clinically earlier and had higher blood lactate levels and lower residual enzyme activities than subjects who were still alive at the time of reporting. Survival bore no relationship to the underlying biochemical or genetic abnormality or to gender.

CONCLUSIONS

Although the clinical spectrum of PDC deficiency is broad, the dominant clinical phenotype includes presentation during the first year of life; neurological and neuromuscular degeneration; structural lesions revealed by neuroimaging; lactic acidosis and a blood lactate:pyruvate ratio ≤20.

PDH E1β deficiency with novel mutations in two patients with Leigh syndrome

Most cases of pyruvate dehydrogenase complex (PDHc) deficiency are attributable to mutations in the PDHA1 gene which encodes the E(1)α subunit, with few cases of mutations in the genes for E(3), E3BP (E(3) binding protein), E(2) and E(1)-phosphatase being reported. Only seven patients with deficiency of the E(1)β subunit have been described, with mutations in the PDHB gene in six of them. Clinically they presented with a non-specific encephalomyopathy. We report two patients with new mutations in PDHB and Leigh syndrome. Patient 1 was a boy with neonatal onset of hyperlactataemia, corpus callosum hypoplasia and a convulsive encephalopathy. After neurological deterioration, he died at age 5 months. Autopsy revealed the characteristic features of Leigh syndrome. Patient 2, also a boy, presented a milder clinical course. First symptoms were noticed at age 16 months with muscular hypotonia, lactic acidosis and recurrent episodes of somnolence and transient tetraparesis. MRI revealed bilateral signal hyperintensities in the globus pallidus, midbrain and crura cerebri. PDHc and E(1) activities were deficient in fibroblasts in patient 1; in patient 2 PDHc deficiency was found in skeletal muscle. Mutations in PDHA1 were excluded. Sequencing of PDHB revealed a homozygous point mutation (c.302T>C), causing a predicted amino acid change (p.M101T) in patient 1. Patient 2 is compound heterozygote for mutations c.301A>G (p.M101V) and c.313G>A (p.R105Q). All three mutations appear to destabilize the E(1) enzyme with a decrease of both E(1)α and E(1)β subunits in immunoblot analysis. To our knowledge, these patients with novel PDHB mutations are the first reported with Leigh syndrome.

FATP1 localizes to mitochondria and enhances pyruvate dehydrogenase activity in skeletal myotubes

Fatty acid transport protein 1 (FATP1) has been previously immunolocalized in intracellular compartments. Here we show that FATP1 localizes to the mitochondria in cultured myotubes, by immunoblots of subcellular fractions and immunocytology of the fusion protein FATP1-GFP. FATP1 strongly stimulates CO(2) production from glucose whereas nonmitochondrial metabolism of glucose is only slightly enhanced. FATP1 raises the activity and activates the pyruvate dehydrogenase (PDH) complex and the pyruvate decarboxylase PDH-E1 catalytic subunit, without changing E2, E3BP or E1alpha and increasing E1beta protein content. These data reveals the localization and points to a regulatory function of FATP1 in myotube mitochondria.

Leigh's disease due to a new mutation in the PDHX gene

OBJECTIVE

To describe the clinical course, neuroradiological presentation, biochemical and molecular studies of a new patient with pyruvate dehydrogenase complex (PDHc) deficiency. To compare this case with the data on other published cases.

METHODS

Brain magnetic resonance imaging (MRI), basal metabolic investigations with lactate measurements in body fluids, PDHc activity assay on cultured skin fibroblasts, immunoblot analysis and molecular studies (polymerase chain reaction [PCR] and sequencing procedures).

RESULTS

Our patient accused an unspecific encephalopathy for years and presented at 13 years of age an acute deterioration with basal ganglia necrosis and subcortical white matter involvement. PDHc deficiency was secondary to a large deletion (3913 bp) in the PDHX gene, which encodes E3 binding protein (E3BP) subunit.

INTERPRETATION

These data provide an additional case of E3BP deficiency with a unique and previously unreported deletion in the PDHX gene.

First characterization of a large deletion of the PDHA 1 gene

Pyruvate dehydrogenase complex (PDC) deficiency is one of the major recognized causes of congenital lactic acidosis. The most common form is due to PDHA 1 gene (Xp22.12) defects. Here, we report the case of a Polynesian girl presenting with delayed neurological development, cortical atrophy, and posterior corpus callosum agenesis. Elevated lactate and pyruvate levels in blood and cerebrospinal fluid suggested PDC deficiency. However, PDC activity was within the normal range in lymphocytes and the direct sequencing of the 11 exons and intron-exon junctions of the PDHA 1 gene did not show any changes. Long-range PCR amplification of the whole gene (16 kb) from blood DNA revealed a heterozygous deletion of approximately 4.2kb. Fine mapping of the deletion breakpoint was achieved using purified long-range PCR products for restriction enzyme analysis and direct sequencing. The deletion removed a 4,227 bp region covering part of intron 5 to part of intron 9 [g.10,145_14,371 del 4,227]. The deletion breakpoint contained a short direct repeat (GTAG), which may be derived either from the upstream or the downstream homologous sequence. The presence of a GAG triplet and inverted repeats in the vicinity of the deletion suggest replication slippage at a polymerase alpha arrest site. This is the first time that a large intragenic deletion of the PDHA 1 gene has been characterized.

Optimized spectrophotometric assay for the completely activated pyruvate dehydrogenase complex in fibroblasts

BACKGROUND

Analysis of the pyruvate dehydrogenase complex (PDHc) activity in human skin fibroblasts is hampered by low enzyme activity in the cells. The most commonly used radiochemical method detects the formation of (14)CO(2), an endproduct of the E1 component of PDHc, from [1-(14)C]pyruvate.

METHODS

We report a spectrophotometric method for the analysis of PDHc activity in fibroblasts based on detection of NADH formation via a p-iodonitrotetrazolium violet (INT)-coupled system. We investigated in detail the specific requirements of this assay, such as cofactor requirements and the effects of suggested stimulatory compounds and different cell disruption procedures. The reliability of the optimized assay was studied by investigation of patients previously diagnosed with PDHc deficiency and by comparison with results from the radiochemical method.

RESULTS

Mean (SD) total PDHc activities were 136 (31) and 58 (21) mU/U of citrate synthase in fibroblast homogenates from 10 healthy volunteers and 7 PDHc-deficient patients, respectively, by the spectrophotometric assay. Similar results were obtained in a mitochondrial fraction. Dithiothreitol (DTT) increased the nonspecific inhibitor-insensitive rate with less pronounced effect on the specific rate of PDHc activity. Administration of DTT increased PDHc activity to 193 (3)% of control activity (without DTT), but decreased the inhibitor-sensitive rate from 99 (0.3)% (without DTT) to 69 (2)% (with 0.3 mmol/L DTT).

CONCLUSION

The simple, optimized spectrophotometric assay for PDHc analysis allows reliable investigation of the enzyme complex in human skin fibroblasts.

Complex approach to prenatal diagnosis of cytochrome c oxidase deficiencies

Different severe disorders of cytochrome c oxidase (COX) have been described in children, but only the defects with autosomal inheritance are suitable for prenatal diagnosis. To perform prenatal diagnosis of fatal infantile COX deficiency a complex approach has been used which combined determination of the genetic origin of the defect, and detailed analysis of the function, content and subunit composition of the enzyme in cultured fetal cells. The tissues and cultured fibroblasts of the patient with Leigh's syndrome showed a COX deficiency of systemic character. The decrease of COX activity to 5-11 per cent was accompanied by proportionally decreased content of the assembled COX enzyme. With the help of transmitochondrial cybrids derived from patient fibroblasts it was proven that the COX defect was of nuclear origin. In a successive pregnancy, the function of oxidative phosphorylation (OXPHOS) was analysed in cultured amniocytes by substrate-stimulated ATP production and COX activity was compared with the activity of citrate synthase. The amount and composition of OXPHOS complexes was estimated by two-dimensional (Blue Native/SDS) polyacrylamide gel electrophoresis and was verified immunochemically with specific antibodies. Three independent lines of evidence provided us with reliable data on the function of COX and OXPHOS in fetal cells which were sufficient to rule out the expected enzymatic defect within three weeks after amniocentesis.

Pyruvate dehydrogenase complex deficiency and altered respiratory chain function in a patient with Kearns-Sayre/MELAS overlap syndrome and A3243G mtDNA mutation

Combined alteration of the pyruvate dehydrogenase complex and respiratory chain function is described in a 21 year-old male patient with overlapping MELAS (mitochondrial encephalomyopathy, lactic acidosis, and 'stroke-like' episodes) and Kearns-Sayre syndrome. Progressive external ophthalmoplegia, pigmentary retinopathy and right bundle branch block were present when he experienced the first 'stroke-like' episode at 18 years old. The A>G tRNALeu(UUR) point mutation at nucleotide 3243 of the mitochondrial DNA was predominant in muscle tissue (79%) and present, but at lower levels in fibroblasts (49%) and blood cells (37%). Biochemical analysis revealed diminished activities of pyruvate dehydrogenase (23%) and respiratory chain complexes I and IV (57%, respectively) in muscle, but normal activities in the fibroblasts. Immunochemical studies of the muscular pyruvate dehydrogenase components showed normal content of E1alpha, E1beta and E2 protein. Molecular screening of the E1alpha gene did not indicate a nuclear mutation. These observations suggest that mitochondrial DNA defects may be associated with altered nuclear encoded enzymes which are actively imported into mitochondria and constitute components of the mitochondrial matrix. Biochemical workup of mitochondrial disorders should not be restricted to the respiratory chain even if mitochondrial DNA mutations are present.

Deficiency of the voltage-dependent anion channel: a novel cause of mitochondriopathy

A patient with a deficient voltage-dependent anion channel (VDAC) is reported, presenting clinically with psychomotor retardation and minor dysmorphic features. Biochemical studies on muscle mitochondria showed impaired rates of pyruvate oxidation and ATP production; however, no specific deficient activity of one of the mitochondrial enzymes was involved. Western blotting experiments indicated an almost complete VDAC deficiency in skeletal muscle. The only moderately decreased VDAC content in the patient's fibroblasts might indicate that VDAC is expressed in a tissue-specific manner. The deficiency is likely caused by a mutation in the HVDAC1 gene or by a distributed posttranslational modification. This is the first described deficiency of a component of the outer mitochondrial membrane associated with the pyruvate oxidation pathway. Defects in this membrane should be considered as a possible cause of otherwise unexplained mitochondrial disorders.

Neonatal De Toni-Debré-Fanconi syndrome due to a defect in complex III of the respiratory chain

A patient with neonatal expression of severe De Toni-Debré-Fanconi syndrome is presented. Because of early signs of renal tubulopathy together with a large urinary excretion of lactate, 3-hydroxybutyrate and citric acid cycle intermediates, a mitochondrial disorder was suspected and muscle and liver biopsies were performed. Biochemical investigations in both tissues revealed a defect in the respiratory chain at the level of complex III. In this patient renal dysfunction was the primary symptom, and hyperlactataemia, an important clue for a mitochondrial disorder, was lacking. CONCLUSION. Complex III deficiency should be included in the differential diagnosis of neonatal De Toni-Debré-Fanconi syndrome.

Altered properties of mitochondrial ATP-synthase in patients with a T-->G mutation in the ATPase 6 (subunit a) gene at position 8993 of mtDNA

A family is described with a T-->G mutation at position 8993 of mtDNA. This mutation is located in the ATPase 6 gene of mtDNA which encodes subunit a of the ATP-synthase complex (FlFo-ATPase). Clinically, the patients showed severe infantile lactate acidosis and encephalomyopathy in a form that was different from the classical Leigh syndrome. In 3 affected boys, ranging in age from 3 months to 8 years, the mutation was found in 95-99% of the mtDNA population. The clinical symptoms correlated with the mtDNA heteroplasmy and in the healthy mother 50% of the mtDNA was mutated. The rate of mitochondrial ATP production by cultured skin fibroblasts containing 99% of mutated mtDNA was about 2-fold lower than that in normal fibroblasts. Native electrophoresis of the mitochondrial enzyme complexes revealed instability of the FlFo-ATPase in all the tissues of the patient that were investigated (heart, muscle, kidney, liver). Only a small portion of the ATP-synthase complex was present in the complete, intact form (620 kDa). Incomplete forms of the enzyme were present as subcomplexes with approx. molecular weights of 460, 390 and 150 kDa, respectively, which differed in the content of F1 and Fo subunits. Immunochemical analysis of the subunits of the FlFo-ATPase further revealed a markedly decreased content of the Fo subunit b in mitochondria from muscle and heart, and an increased content of the Fo subunit c in muscle mitochondria, respectively. These results indicate that in this family the T-->G point mutation at position 8993 in the mitochondrial ATPase 6 gene is accompanied by structural instability and altered assembly of the enzyme complex, that are both most likely due to changes in the properties of subunit a of the membrane sector part of the ATP-synthase.

Congenital lacticacidemia caused by lipoamide dehydrogenase deficiency with favorable outcome

A 5-year-old boy had recurrent vomiting and lethargy with lacticacidemia and ketoacidemia since birth. Lipoamide dehydrogenase deficiency was found in muscle and fibroblasts. Therapy with sodium dichloroacetate, thiamine, and carnitine was associated with reduction of the severity and frequency of the decompensation episodes and near normal plasma lactate levels. At 5 years of age, the patient has normal cognitive function and moderate motor impairment.

Familial mitochondrial encephalopathy with fetal ultrasonographic ventriculomegaly and intracerebral calcifications

In two sibs antenatal ultrasonography revealed identical intracranial calcification, ventricular widening and microcephaly. The first pregnancy was artificially terminated at 19 weeks. Post-mortem examination of the brain revealed destructive calcification and extracerebral neuronal heterotopia. The second sib went to term but died 48 h after birth from irreversible lactic acidosis. Autopsy showed extensive encephalopathy with cavitation and calcification in the cerebral hemispheres, polymicrogyria, multiple neuronal heterotopia, partial callosal dysgenesis, and severe Leigh syndrome, together forming a continuum of early and late brain disruption. Mitochondrial respiratory chain abnormalities, mainly affecting complexes I and IV, and deficiency of pyruvate dehydrogenase complex were detected in skeletal muscle and in liver. A normal functioning of the respiratory chain was found in the fibroblasts. Analysis of mtDNA from muscle, liver and blood revealed normal amounts of intact mtDNA without any of the known point mutations associated with MELAS, MERRF or Leigh syndromes. The early fetal disruption and necrotic changes in the brains of sibs indicate a specific genetically determined disorder which affects neuronal migration, a finding not previously associated with respiratory chain disorders. The present disorder may mimic antenatal congenital infectious encephalopathy because of the combined finding of microcephaly and destructive intracerebral calcification.

Extreme variability of clinical symptoms among sibs in a MELAS family correlated with heteroplasmy for the mitochondrial A3243G mutation

In a family with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes with extremely varying clinical expression, we have identified the A3243G heteroplasmic point mutation in mitochondrial DNA. The degree of severity of the clinical symptoms in the various family members was reflected in the relative quantity of mutated mitochondrial DNA in different tissues. The biochemical activity of complex I of the respiratory chain in muscle was decreased in some members of this family.

Mitochondrial creatine kinase activity in patients with disturbed energy generation in muscle mitochondria

Eleven patients with an established disturbance in muscle mitochondrial energy generation, in whom no defect in the pyruvate dehydrogenase complex or in the complexes of the respiratory chain could be detected, were investigated for a possible deficiency of mitochondrial creatine kinase (Mi-CK) (EC 2.7.3.2). Four patients with a defect in one of the complexes of the respiratory chain were also investigated for Mi-CK activity. In none of the investigated patients was Mi-CK deficiency found. Surprisingly, two of the four patients with a defect in one of the respiratory chain complexes showed enhanced activity of Mi-CK. It is concluded that Mi-CK deficiency is not frequently found as a primary defect in patients with disturbance in mitochondrial energy generation, but more patients should be examined to allow a definite conclusion.

Treatment of complex I deficiency with riboflavin

We have evaluated the effects of treatment with riboflavin in five patients with a mitochondrial myopathy, associated with a complex I (NADH dehydrogenase) deficiency. Two patients suffered from a clinically pure myopathy and the other patients presented with encephalomyopathic features. Treatment with riboflavin resulted in a clear clinical improvement in the two patients with the myopathic form of complex I deficiency. However, only one of the patients with the encephalomyopathic form improved during therapy. In three of the four patients in whom complex I activity in muscle tissue has been determined again during therapy, complex I activity appeared to be normalized. The clinical effects of treatment in this group of patients do not correlate well with normalization of complex I activity.

Enzyme activities of the mitochondrial energy generating system in skeletal muscle tissue of preterm and fullterm neonates

Quadriceps muscle specimens from autopsy of 28 neonates (gestational age 25-42 weeks) were investigated to determine pyruvate and malate oxidation rates and several enzymes of the mitochondrial oxidative process. In general, the levels of all mitochondrial parameters measured, including carnitine levels, were lower in the neonates who died within the first week of life than those in the control group (age > 5 years). Pyruvate and malate oxidation rates (P < 0.05), activities of pyruvate dehydrogenase complex (P < 0.10) and succinate: cytochrome c oxidoreductase (P < 0.05) increased significantly with gestational age. Pyruvate oxidation rates (P < 0.05) as well as activities of citrate synthase (P < 0.05) and NADH:Q1 oxidoreductase (P < 0.05) were significantly lower in the group of very preterm infants at an age of 1-7 days compared with very preterm infants at an age between 3-8 weeks. We conclude from our study that special reference values are necessary for a correct biochemical diagnosis of mitochondrial encephalomyopathies in the neonatal period. Differences between preterm and fullterm children of the same age (1 week) indicate a maturational process in human muscle tissue during gestation. Comparison of two different age groups within the very preterm neonates point to a postnatal maturation of the mitochondrial energy metabolism, at least in preterm neonates.

Combined deficiencies of the pyruvate dehydrogenase complex and enzymes of the respiratory chain in mitochondrial myopathies

In six patients with mitochondrial (encephalo-) myopathy investigations of skeletal muscle revealed a defect of pyruvate dehydrogenase complex (PDHC) in combination with one or more respiratory chain complex deficiencies. A combination of defects of this kind has not been reported previously. Five of the six patients presented within the 1st year of life and had a severe clinical course. Intrafamilial variability of the clinical course in dizygotic twins both suffering from a cytochrome c oxidase deficiency and one of them also from a PDHC deficiency suggests an additional effect of PDHC deficiency on the clinical symptoms. Immunoblot studies of PDHC in five of the patients revealed no abnormalities in their subunit pattern, rendering a defect of mitochondrial protein import or assembly unlikely. The finding of a combined PDHC and respiratory chain deficiency has implications for the diagnostic approach, for therapy and genetic counselling. The exact pathogenetic mechanism of this combination of defects remains to be elucidated.

Assessment and therapy monitoring of Leigh disease by MRI and proton spectroscopy

In a 2-year-old boy with Leigh disease, spasticity, dysarthria, and optic atrophy gradually developed. Computed tomography and magnetic resonance imaging disclosed progressive, symmetric basal ganglia lesions. In muscle tissue, a defect of pyruvate dehydrogenase complex was found. Magnetic resonance volume selective proton spectroscopy (MRVS) of the basal ganglia demonstrated an abnormal lactate peak. A ketonemic diet coincided with clinical stabilization and arrest of progressive brain lesions. Lactate could no longer be demonstrated by MRVS. It reappeared with a new brain lesion coinciding with discontinuation of the diet. MRVS, therefore, appears to be a sensitive tool to evaluate pathologic lactate production in metabolic brain disease with disturbed energy metabolism and allows noninvasive therapy monitoring.

Myopathology and a mitochondrial DNA deletion in the Pearson marrow and pancreas syndrome

A patient with the Pearson marrow and pancreas syndrome is presented. She showed an anaemia with neutropenia and thrombopenia, failure to thrive, diarrhoea, disturbed glucose homeostasis and lactic acidosis. An exocrine pancreatic insufficiency was lacking. The disease followed a fatal course. Biochemical investigations of skeletal muscle revealed a disturbed mitochondrial energy metabolism, while many ultrastructural abnormal features were observed in the muscle tissue. Molecular genetic studies showed a de novo deletion in the mitochondrial DNA (mtDNA), different in size from the already published deletions and flanked by two 4 bp direct repeats, interspaced by 4-5 non-repeated nucleotides. mtDNA from 12 other tissues showed the same deletion in different percentages. No obvious relation between these percentages and tissue dysfunction was found. In spite of an open reading frame of 74 codons, only little transcription product of the genomic region resulting from the deletion was found.