  Prenat. Diagn. 19: 921–926 (1999) Fetal Muscle Biopsy as a Diagnostic Tool in Duchenne Muscular Dystrophy Yoram Nevo 1,3 *, Ruth Shomrat 2 , Yuval Yaron 2,3 , Avi Orr-Urtreger 2,3 , Shaul Harel 1,3 and Cyril Legum 2,3 1 Institute for Child Development and Pediatric Neurology Unit, Dana Children’s Hospital, Tel-Aviv, Israel 2 Genetic Institute, Tel-Aviv-Sourasky Medical Center, Tel-Aviv, Israel 3 Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, Israel Duchenne muscular dystrophy (DMD) is a relentless progressive disorder, leading to severe disability during childhood and death in adolescence or early adulthood. In most families, prenatal diagnosis is readily achieved by molecular detection of DNA deletions using chorionic villi or amniocytes, or by linkage analysis. In some cases, however, molecular methods fail to provide a definitive diagnosis and in such cases in utero fetal muscle biopsy may serve as a diagnostic option. We describe three families in whom fetal muscle biopsy was performed, focusing on the prenatal diagnostic dilemmas, the indications and timing for in utero fetal muscle biopsy, and the difficulties encountered. Copyright  1999 John Wiley & Sons, Ltd.  : Duchenne muscular dystrophy; fetal muscle biopsy; prenatal diagnosis INTRODUCTION Duchenne muscular dystrophy (DMD) is the most common childhood muscular dystrophy with an inci- dence of 1 in 3500 live male births (Evans et al., 1991). The disease has a severe, progressive course resulting in death during adolescence or early adulthood (Hoffman et al., 1988). The disease is caused by mutations in the dystrophin gene which has been mapped to the short arm of chromosome X (Xp21), cloned and identified (Koenig et al., 1987). The gene product, dystrophin,a 427 kd protein, is localized to the sarcolemma (Arahata et al., 1988; Bonilla et al., 1988; Zubrzycka- Gaarn et al., 1988). It is either absent or greatly reduced in quantity in DMD patients (Hoffman et al., 1988; Bonilla et al., 1988; Miranda et al., 1988; Patel et al., 1988). Intragenic deletion or duplication of the dystrophin gene is found in about 65 per cent of patients with DMD (Koenig et al., 1987; den Dunnen et al., 1989). In these cases the mutation can readily be identified in other affected family members. Prenatal diagnosis is therefore feasible using DNA from chorionic villi or amniotic fluid cells (Evans et al., 1991). In the 35 per cent of families without deletion or duplications, pre- natal diagnosis may be problematic. In many of these families diagnosis by linkage analysis is an option (Bakker et al., 1985). However, linkage analysis is not possible in all cases. Only about two-thirds of cases are inherited through a carrier mother, whereas one-third are sporadic, resulting from de novo mutations of the dystrophin gene (Moser, 1984). In such sporadic cases and in small families, linkage analysis may be imprac- tical because of non-informativity of maternal haplotypes or a crossover event (Clerk et al., 1992). In families in which molecular methods cannot pro- vide a definitive prenatal diagnosis, fetal muscle biopsy in utero is an option (Evans et al., 1991, 1993, 1994). We present three cases where fetal muscle biopsy was performed and discuss some of the indications and difficulties in performing such a procedure for diagnostic and genetic counselling purposes. CASE REPORTS Family 1 DMD was diagnosed in two young male siblings and confirmed by immuno-histochemistry. Their mother, an obligatory carrier, inherited her paternal X chromo- some (P1) from a clinically unaffected father (Fig. 1). No deletion of the dystrophin gene has been found in the two affected siblings. Even though the most likely situation in this family would be a new mutation arising in a single sperm of the boys’ maternal grand- father, gonadal mosaicism in the grandfather cannot be excluded. The consultand in this case was the mother’s sister who was pregnant with a male fetus. Her haplotype had an intragenic crossover distal to XJ 2.3 (M1/M2). Her fetus’ haplotype carried the distal portion of M1 and a second crossover, which included part of her paternally-inherited chromosome (M1/P1) (Fig. 1). The mother’s pregnant sister elected to undergo a fetal muscle biopsy because of a theoretical risk of 7–14 per cent for paternal gonadal mosaicism (Bakker et al. 1989). Immuno-histochemical evaluation showed normal dystrophin staining, confirming the presence of an unaffected fetus. Family 2 The consultant is a carrier of DMD. Her brother and a half uncle were affected and died in their late teens *Correspondence to: Y. Nevo, The Institute for Child Development, 14 Balfour Street, Tel-Aviv, Israel, 65211, Israel. E-mail: nevo@tasmc.health.gov.il CCC 0197–3851/99/100921–06$17.50 Copyright  1999 John Wiley & Sons, Ltd. Received 10 February 1999 Revised 6 May 1999 Accepted 12 May 1999