SHORT REPORT X-inactivation of HSD17B10 revealed by cDNA analysis in two female patients with 17b-hydroxysteroid dehydrogenase 10 deficiency Judit Garcı ´a-Villoria 1,2 , Laura Gort 1,2 , Irene Madrigal 2,3 , Carme Fons 2,4 , Cristina Ferna ´ndez 1,2 , Aleix Navarro-Sastre 1,2 , Montserrat Mila ` 2,3 , Paz Briones 1,2,5 , Angeles Garcı ´a-Cazorla 2,4 , Jaume Campistol 2,4 and Antonia Ribes* ,1,2 17b-Hydroxysteroid dehydrogenase 10 (HSD10) is a mitochondrial enzyme involved in the degradation pathway of isoleucine and branched-chain fatty acids. The gene encoding HSD10, HSD17B10, has been reported as one of the few genes that escapes X-inactivation. We previously studied two female patients with HSD10 deficiency, one of them was severely affected and the other presented a mild phenotype. To elucidate as to why these two carriers were so differently affected, cDNA analyses were performed. The HSD17B10 cDNA of eight control cell lines, two hemizygous patients and two carriers was obtained from cultured fibroblasts, amplified by PCR and sequenced by standard methods. All HSD17B10 cDNAs were quantified by real-time PCR. In the fibroblasts of the female patient who presented with the severe phenotype, only the mutant allele was identified in the cDNA sequence, which was further confirmed by relative quantification (RQ) of HSD17B10 cDNA. This is in agreement with an unfavourable X-inactivation. The other female patient, with slight clinical affectation, showed the presence of both mutant and wild-type alleles in the cDNA sequence, which was confirmed by RQ of HSD17B10 cDNA in fibroblasts. This is in line with normal X-inactivation and the expression of both alleles in different cells (functional mosaicism). RQ results of HSD17B10 cDNA did not differ significantly between male and female controls, which indicate that the genetic doses of mRNA of HSD17B10 was the same in both sexes. In conclusion, these results suggest that the HSD17B10 gene does not escape X-inactivation as has been reported previously. European Journal of Human Genetics (2010) 18, 1353–1355; doi:10.1038/ejhg.2010.118; published online 28 July 2010 Keywords: HSD10 deficiency; HADH2; HSD17B10 INTRODUCTION 17b-Hydroxysteroid dehydrogenase 10 (HSD10) is a mitochondrial enzyme involved in the degradation pathway of isoleucine and branched-chain fatty acids. 1 This enzyme has also been found to be involved in the metabolism of sex steroid hormones, neuroactive steroids and in the detoxification of cytotoxic aldehydes. 2,3 HSD10 deficiency (OMIM 300256) is an X-linked defect caused by mutations in the HSD17B10 gene. Clinically, the great majority of male patients show normal early development followed by progressive loss of mental and motor skills. 1,4–11 However, three patients were identified who presented symptoms in the first days of life. 1,11 It has recently been shown that symptoms of these patients are unrelated to accumulation of metabolites in the isoleucine pathway and that the neurological handicap can be associated with an imbalance in neurosteroid metabolism 12 or to defects in general mitochondrial function. 13 In addition, the splice variant c.574C4A of HSD17B10 gene has been associated with a new syndromic form of X-linked mental retardation, choreoathetosis and abnormal behaviour. 14 The HSD17B10 gene has been mapped to chromosome Xp11.2 15 and has been reported as one of the few genes that escapes X-inactivation. 16 To date, 10 female patients with HSD10 deficiency have been described presenting a variety of symptoms, from border- line learning difficulties to psychomotor and speech delay. 5,9,11 We previously studied two of these female patients. One of them was heterozygous for the p.N247S mutation and was severely affected, whereas the other was heterozygous for the p.P210S mutation and presented a slight clinical affectation. 11 To elucidate as to why these two female patients were so differently affected, we performed HSD17B10 cDNA quantitative analysis in both female patients and in control fibroblasts, the results of which are reported here. MATERIALS AND METHODS Material Skin biopsies from patients of two unrelated Spanish families with HSD10 deficiency were obtained: family 1 consisting of a male patient (1IIM) and his carrier sister (1IIF), both with a severe phenotype (Figure 1a); family 2 consisting of a male patient (2IIM), with a severe phenotype, and his heterozygous mother (2IF), with a slight clinical affectation (Figure 1a). Both families have been described previously. 11 Eight cell lines (four males and four females) from our cell bank were used as controls. Received 19 October 2009; revised 16 June 2010; accepted 16 June 2010; published online 28 July 2010 1 Seccio ´n de Errores Conge ´nitos del Metabolismo (IBC), Servicio de Bioquı ´mica y Gene ´tica Molecular, Hospital Clı´nic, IDIBAPS, Barcelona, Spain; 2 CIBER of Rare Diseases (CIBERER), Barcelona, Spain; 3 Seccio ´ n de Gene ´ tica Molecular, Servicio de Bioquı ´mica y Gene ´tica Molecular, Hospital Clı´nic, IDIBAPS, Barcelona, Spain; 4 Servicio de Neurologı ´a, Hospital Sant Joan de De ´u, Barcelona, Spain; 5 CSIC, Barcelona, Spain *Correspondence: Dr A Ribes, Seccio ´n de Errores Conge ´nitos del Metabolismo (IBC), Servicio de Bioquı´mica y Gene ´tica Molecular, CIBER de Enfermedades Raras (CIBERER), Hospital Clı´nic, C/ Mejı ´a Lequerica, s/n, Edifici Helios III, Barcelona 08028, Spain. Tel: +34 93 227 9340; Fax: +34 93 227 5668; E-mail: aribes@clinic.ub.es European Journal of Human Genetics (2010) 18, 1353–1355 & 2010 Macmillan Publishers Limited All rights reserved 1018-4813/10 www.nature.com/ejhg