A Diagnostic Algorithm for Mitochondrial Disorders in Estonian Children

Mitochondrial disorders are a heterogeneous group of disorders affecting energy production of the body. Different consensus diagnostic criteria for mitochondrial disorders in childhood are available - Wolfson, Nijmegen and modified Walker criteria. Due to the extreme complexity of mitochondrial disorders in children, we decided to develop a diagnostic algorithm, applicable in clinical practice in Estonia, in order to identify patients with mitochondrial disorders among pediatric neonatology and neurology patients. Additionally, it was aimed to evaluate the live-birth prevalence of mitochondrial disorders in childhood. During the study period (2003-2009), a total of 22 children were referred to a muscle biopsy in suspicion of mitochondrial disorder based on the preliminary biochemical, metabolic and instrumental investigations. Enzymatic and/or molecular analysis confirmed mitochondrial disease in 5 of them - an SCO2 gene (synthesis of cytochrome c oxidase, subunit 2) defect, 2 cases of pyruvate dehydrogenase complex deficiency and 2 cases of combined complex I and IV deficiency. The live-birth prevalence for mitochondrial defects observed in our cohort was 1/20,764 live births. Our epidemiological data correlate well with previously published epidemiology data on mitochondrial diseases in childhood from Sweden and Australia, but are lower than in Finland.

Whole Xp Deletion in a Girl with Mental Retardation, Epilepsy, and Biochemical Features of OTC Deficiency

Background: Females with a total or partial deletion of the short arm of the X chromosome have variable features of Turner syndrome, but mental retardation (MR) rarely occurs. The haploinsufficiency of deleted genes that escape X-inactivation may explain the occurrence of MR and autism. Ornithine transcarbamylase (OTC) deficiency is the most common urea cycle disorder and is inherited in an X-linked semi-dominant trait, and the OTC gene maps to Xp21. Methods: We report on a girl with MR, epilepsy and biochemical changes characteristic of OTC deficiency but no identifiable point mutation in the OTC gene. Standard G-banding cytogenetic analysis, whole genome karyotyping, and X-inactivation studies were performed to determine the genetic etiology of the OTC deficiency in the patient. Results: Cytogenetic analysis and molecular karyotyping using SNP array revealed a deletion of the whole short arm of the X chromosome (Xp22.33-p11.1). Inactivation studies also revealed a completely skewed X-inactivation. Conclusion: Our patient presented with MR, epilepsy, and some evidence of reduced OTC activity, but performed genetic studies gave no explanation for this phenotype. We hope that this case report contributes to the understanding of the underlying genetic factors of the manifestation of X-linked disorders in female patients.

Prevalence of Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency in Estonia

The aim of our study was to evaluate the prevalence of long chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) in the general Estonian population and among patients with symptoms suggestive of fatty acid oxidation (FAO) defects. We collected DNA from a cohort of 1,040 anonymous newborn blood spot samples. We screened these samples for the presence of the common c.1528G>C mutation in the HADHA gene. Based on the clinical suspicion of FAO defects, we screened suspected individuals since 2004 for the common c.1528G>C mutation in the HADHA gene and since 2008 in addition by tandem mass spectrometric analysis of plasma acylcarnitines. Our results showed that the carrier frequency of the c.1528G>C mutation in the Estonian population is high - 1:173. During the screening of symptomatic patients, we identified five LCHADD patients in four families. Three patients were retrospectively identified by molecular screening of the HADHA gene. One patient was homozygous for the c.1528G>C mutation in the HADHA gene, and two siblings were compound heterozygotes with HADHA genotype c.[1528G>C]+[1690-2A>G]. Among patients tested using acylcarnitine profiling, we identified two cases with an abnormal acylcarnitine profile typical to LCHADD. Molecular analysis showed homozygosity for c.1528G>C mutation. Based on a carrier frequency of 1:173 (95% Confidence Interval 1:76-1:454) and taking into account that the c.1528G>C mutation makes up 87.5% of disease alleles in Estonian LCHADD patients, the estimated prevalence of LCHADD in Estonia would be 1: 91,700.

A Boy with Holt-Oram Syndrome Caused by Novel Mutation c.1304delT in the TBX5 Gene

Holt-Oram syndrome (HOS) is an autosomal dominant developmental defect involving preaxial radial ray upper limb deformity and variable cardiac defects. It has been demonstrated that HOS is caused by mutations in the T-box transcription factor gene TBX5. Numerous germline mutations (more than 60) of this gene produce preterminal stop codons, which lead to synthesis of a truncated nonfunctional TBX5 protein. The haplo-insufficiency of the TBX5 gene is the most significant cause of HOS. We report on a sporadic patient with clinical features of HOS. Our patient had a cardiac anomaly - a muscular ventricular and atrial septal defect, patent ductus arteriosus and a conduction defect (a first-step atrioventricular block). Upper limb anomalies in our patient were relatively mild and unusual to HOS - distally displaced thumbs, narrow shoulders and hypotrophy of the muscles in the shoulder region. Molecular analysis identified a novel and unusual heterozygous frameshift mutation - c.1304delT (p.Leu435fsX146) - in exon 9 of the TBX5 gene, which is predicted to cause an elongated TBX5 protein with 84 miscoding amino acids and 62 supernumerary C-terminal amino acids. To the best of our knowledge, only one such type of elongation mutation has thus far been reported in the TBX5 gene.

Further delineation of the 15q13 microdeletion and duplication syndromes: a clinical spectrum varying from non-pathogenic to a severe outcome

BACKGROUND

Recurrent 15q13.3 microdeletions were recently identified with identical proximal (BP4) and distal (BP5) breakpoints and associated with mild to moderate mental retardation and epilepsy.

METHODS

To assess further the clinical implications of this novel 15q13.3 microdeletion syndrome, 18 new probands with a deletion were molecularly and clinically characterised. In addition, we evaluated the characteristics of a family with a more proximal deletion between BP3 and BP4. Finally, four patients with a duplication in the BP3-BP4-BP5 region were included in this study to ascertain the clinical significance of duplications in this region.

RESULTS

The 15q13.3 microdeletion in our series was associated with a highly variable intra- and inter-familial phenotype. At least 11 of the 18 deletions identified were inherited. Moreover, 7 of 10 siblings from four different families also had this deletion: one had a mild developmental delay, four had only learning problems during childhood, but functioned well in daily life as adults, whereas the other two had no learning problems at all. In contrast to previous findings, seizures were not a common feature in our series (only 2 of 17 living probands). Three patients with deletions had cardiac defects and deletion of the KLF13 gene, located in the critical region, may contribute to these abnormalities. The limited data from the single family with the more proximal BP3-BP4 deletion suggest this deletion may have little clinical significance. Patients with duplications of the BP3-BP4-BP5 region did not share a recognisable phenotype, but psychiatric disease was noted in 2 of 4 patients.

CONCLUSIONS

Overall, our findings broaden the phenotypic spectrum associated with 15q13.3 deletions and suggest that, in some individuals, deletion of 15q13.3 is not sufficient to cause disease. The existence of microdeletion syndromes, associated with an unpredictable and variable phenotypic outcome, will pose the clinician with diagnostic difficulties and challenge the commonly used paradigm in the diagnostic setting that aberrations inherited from a phenotypically normal parent are usually without clinical consequences.

Three patients with 9p deletions including DMRT1 and DMRT2: A girl with XY complement, bilateral ovotestes, and extreme growth retardation, and two XX females with normal pubertal development

It is well documented that distal 9p monosomy can be associated with XY sex reversal. Recently, the possibility of DMRT1 and/or DMRT2 (the genes for doublesex and mab-3 related transcription factor 1 and 2) being the sex determining genes(s) at 9p has been raised. DMRT1 and DMRT2 map near the 9p telomere, distal of marker D9S1779. We describe here three unrelated females with distal 9p monosomy, one with XY complement and two with XX complements. In each individual, fluorescent in situ hybridization predicted the loss of the DMRT genes. Patient 1, an XY individual with monosomy 9pter --> p24.1 approximately 24.2 and trisomy 7q32 --> qter had normal female external genitalia, a blind ending vagina, no uterus, a Fallopian tube on the right, and bilateral ovotestes with primitive ovarian tissue. She also had extreme growth retardation. Around 80 cases of distal 9p monosomy have been reported previously, but there has been no report of ovotestes or gonads comprising ovarian tissue in a XY patient with 9p deletion. Findings in Patient 1 suggest that the phenotypic spectrum of the heterozygous DMRT deletion may include true hermaphroditism. Patients 2 and 3 were 12- and 14-year-old females with XX complements, normal external genitalia, and normal pubertal development. Patient 2 had pure monosomy 9pter --> p23 and Patient 3 had monosomy 9pter --> p22.3 approximately 23 combined with trisomy 3pter --> p23 approximately 24. To date, detailed reports on the gonadal status of XX 9p-females have been limited to prepubertal girls. Patients 2 and 3 are the first females reported to have distal 9p monosomy and a normal puberty.

Sudden death of a girl with Prader-Willi syndrome

We report on the sudden death of a 3.5-year-old girl with Prader-Willi syndrome (PWS) and 15q11-q13 deletion. She suffered from severe chronic breathing disturbances and recurrent bronchitis. During an episode of acute bronchitis she had a cardiac arrest and died two months later of the sequelae. Brain CT imaging three weeks after the arrest showed bilateral symmetrical haemorrhages in the basal ganglia region. The spatial distribution of the haemorrhages can possibly suggest that the basal ganglia in PWS may be especially susceptible to hypoxemia.

Boy with celiac disease, malformations, and ring chromosome 13 with deletion 13q32-->qter

We describe a 2(1/2)-year-old boy with a ring chromosome 13 with distal deletion of 13q32-->qter and celiac disease.

Mutation 985A>G in the MCAD gene shows low incidence in Estonian population

Medium-chain acyl-CoA dehydrogenase (MCAD) is an enzyme responsible for large part of mitochondrial beta-oxidation of fatty acids and therefore stays on key position of cellular energy supply. In case of its deficiency, starvation, rapid growth periods or infections may cause fatal lack of energy, especially in the first years of life. MCAD deficiency is inherited in an autosomal recessive manner and it has been shown to be rather common in some European countries (Great Britain 1 in 6,000, Switzerland 1 in 10,000). In Caucasoid populations one mutation, the 985A>G transition, causing the amino acid substitution K329E, accounts for about 90% of all mutant MCAD alleles. Here we present data about screening the Estonian population for this mutation. We analyzed the DNA from 1,098 persons from all regions of Estonia (all newborns born in one month) and found 5 heterozygotes for 985A>G, that makes the carrier frequency 1 in 220 and the frequency of possibly affected homozygotes 1 out of 193,000. No mutant alleles were found among the samples of the children, who had unclear diagnosis for death during the years 1994 and 1995.

Familial Williams-Beuren syndrome

Williams-Beuren syndrome (WBS) occurs sporadically; however, at least four familial cases of WBS have been described previously. We describe a mother and her son with typical WBS. The diagnosis of WBS in the son was confirmed by molecular cytogenetic analysis fluorescence in situ hybridization. He had a deletion of 7q11.23 at the ELN locus. The mother was diagnosed after the identification of WBS in her affected son. She is deceased and was thus not studied by FISH. However, her combined symptoms make it very clear that she had WBS. Two traits uncommon in WBS were observed, unilateral renal hypoplasia in the mother and a hemivertebra at L5 in the son.

Development of the phenylketonuria screening programme in Estonia

OBJECTIVE

To develop the phenylketonuria (PKU) screening programme in Estonia.

METHOD

All data about patients with PKU, born during 1980-92, were documented to establish its prevalence at birth in Estonia. Newborn screening for the diagnosis and treatment of PKU was started in Estonia in 1993 and the prevalence at birth established by screening. Phenylalanine was determined from filter paper blood by a modified fluorometric method based on enhancement of the fluorescence of a phenylalanine-ninhydrin reaction product by L-leucyl-L-alanine.

RESULTS

During three years (1993-5) 36,074 newborns (85% of the total) were screened for PKU. PKU was diagnosed in six cases during the first four to six weeks of life. All investigated cases could be classified as classical PKU. No cases of mild forms of hyperphenylalaninaemia were diagnosed. The retrospective study showed an average incidence of PKU of 1 in 8090, the prospective study identified a comparable incidence of 1 in 6010 live births.

CONCLUSION

The prevalence at birth of classic PKU in Estonia is higher than the average in Europe and similar to that of some eastern and middle European countries.

Two sisters with growth failure, microcephaly, peculiar facies and apical dystrophy: the presentation of brachymorphism-onychodysplasia-dysphalangism syndrome?

We report two sisters with growth failure, relative microcephaly, peculiar facies and apical dystrophy (brachydactyly type B). They had shortness and clinodactyly of the 5th fingers, aplasia or hypoplasia of the distal phalanges of 5th fingers, short medial phalanges of the 2nd and 5th fingers, hypoplasia or aplasia of distal phalanges of 2-5th toes, with tiny toenails, and aplasia or nails of 5th fingers and right 5th toe in the younger sister. Dysmorphic facial features included high forehead, sparse hair, blepharophimosis, telecanthus, epicanthic folds, a low nasal bridge, a broad nasal tip and micrognathia. Their ears were low-set and malformed. The older sister additionally had a high-pitched voice and eczema on the face and limbs. In the younger sister a cardiac defect was diagnosed--ventricular and atrial septal defect, patent ductus arteriosus. They had some clinical features of Coffin-Siris syndrome, but with a milder phenotype and much less severe mental handicap. Their clinical picture resembles more the brachymorphism-onychodysplasia-dysphalangism (BOD) syndrome.

Phenylalanine hydroxylase gene mutation R408W is present on 84% of Estonian phenylketonuria chromosomes

Phenylalanine hydroxylase (PAH) is the enzyme which converts phenylalanine into tyrosine. In case of its deficiency, hyperphenylalaninemia is observed, which leads to phenylketonuria (PKU), a disease causing mental retardation, unless treated with a low-phenylalanine diet since early childhood. In Estonia, PKU is among the most common inherited metabolic diseases. The data from retrospective study and newborn screening show an approximate incidence of 1 in 6,000 newborns. Molecular analysis of 34 Estonian patients has revealed high genotypic homogeneity in this group, as 84% of the mutant alleles carry the R408W mutation. The high rate of this mutation in the Estonian population rises the speculation of Finno-Ugric contribution to the East European pool of mutant PAH alleles. Five more mutations-IVS12nt1, R261Q, R252W, R158Q, S349P-have been detected. The mutation detection rate was 92% among the studied patients.