Childhood muscular dystrophy: an African review

Impact of PYROXD1 deficiency on cellular respiration and correlations with genetic analyses of limb-girdle muscular dystrophy in Saudi Arabia and Sudan

Next-generation sequencing is commonly used to screen for pathogenic mutations in families with Mendelian disorders, but due to the pace of discoveries, gaps have widened for some diseases between genetic and pathophysiological knowledge. We recruited and analyzed 16 families with limb-girdle muscular dystrophy (LGMD) of Arab descent from Saudi Arabia and Sudan who did not have confirmed genetic diagnoses. The analysis included both traditional and next-generation sequencing approaches. Cellular and metabolic studies were performed on Pyroxd1 siRNA C2C12 myoblasts and controls. Pathogenic mutations were identified in eight of the 16 families. One Sudanese family of Arab descent residing in Saudi Arabia harbored a homozygous c.464A>G, p.Asn155Ser mutation in PYROXD1, a gene recently reported in association with myofibrillar myopathy and whose protein product reduces thiol residues. Pyroxd1 deficiency in murine C2C12 myoblasts yielded evidence for impairments of cellular proliferation, migration, and differentiation, while CG10721 (Pyroxd1 fly homolog) knockdown in Drosophila yielded a lethal phenotype. Further investigations indicated that Pyroxd1 does not localize to mitochondria, yet Pyroxd1 deficiency is associated with decreased cellular respiration. This study identified pathogenic mutations in half of the LGMD families from the cohort, including one in PYROXD1. Developmental impairments were demonstrated in vitro for Pyroxd1 deficiency and in vivo for CG10721 deficiency, with reduced metabolic activity in vitro for Pyroxd1 deficiency.

Variable disease severity in Saudi Arabian and Sudanese families with c.3924 + 2 T > C mutation of LAMA2

BACKGROUND

Congenital muscular dystrophy type 1A is caused by mutations in the LAMA2 gene that encodes the laminin α2 chain, a component of the skeletal muscle extracellular matrix protein laminin-211. The clinical spectrum of the disease is more heterogeneous than previously thought, particularly in terms of motor achievement and disease progression. We investigated clinical findings and performed molecular genetic analysis in 3 families from Saudi Arabia and 1 from Sudan in whom congenital muscular dystrophy 1A was suspected based on homozygosity mapping and laminin α2 chain deficiency.

METHODS

We investigated 9 affected individuals from 1 Sudanese and 3 Saudi families in whom MDC1A was suggested by clinical, neuroimaging and/or pathological findings and by homozygosity mapping at the LAMA2 locus. Morphological and immunohistochemical analysis were performed in 3 patients from the 3 Saudi families. SSCP analysis, DNA sequencing and microsatellite analysis were carried out in the 4 index cases.

RESULTS

A previously described mutation in the LAMA2 gene, a homozygous T > C substitution at position +2 of the consensus donor splice site of exon 26, was found in the 4 index patients. Clinical evaluation of 9 patients from the 4 families revealed variable disease severity particularly as regards motor achievement and disease progression. Microsatellite analysis showed an identical mutation-associated haplotype in the 4 index cases indicating a founder effect of the mutation in all 4 families.

CONCLUSIONS

Our data provide further evidence that the clinical spectrum of MDC1A due to a single mutation is heterogeneous, particularly in terms of motor achievement and disease progression, making it difficult to give a reliable prognosis even in patients with identical LAMA2-associated haplotype. The c.3924 + 2 T > C mutation to date has been found only in patients originating from the Middle East or Sudan; therefore laminin 2 chain deficiency in patients from those regions should initially prompt a search for this mutation.

From dystrophinopathy to sarcoglycanopathy: evolution of a concept of muscular dystrophy

Duchenne and Becker muscular dystrophies are collectively termed dystrophinopathy. Dystrophinopathy and severe childhood autosomal recessive muscular dystrophy (SCARMD) are clinically very similar and had not been distinguished in the early 20th century. SCARMD was first classified separately from dystrophinopathy due to differences in the mode of inheritance. Studies performed several years ago clarified some immunohistochemical and genetic characteristics of SCARMD, but many remained to be clarified. In 1994, the sarcoglycan complex was discovered among dystrophin-associated proteins. Subsequently, on the basis of our immunohistochemical findings which indicated that all components of the sarcoglycan complex are absent in SCARMD muscles, and the previous genetic findings, we proposed that a mutation of any one of the sarcoglycan genes leads to SCARMD. This hypothesis explained and predicted various characteristics of SCARMD at the molecular level, most of which have been verified by subsequent discoveries in our own as well as various other laboratories. SCARMD is now called sarcoglycanopathy, which is caused by a defect of any one of four different sarcoglycan genes, and thus far mutations in sarcoglycan genes have been documented in the SCARMD patients. In this review, the evolution of the concept of sarcoglycanopathy separate from that of dystrophinopathy is explained by comparing studies on these diseases.

Childhood neuromuscular disorders: a decade's experience in Saudi Arabia

The study describes the pattern of childhood neuromuscular disorders seen in a decade (1982-1992) at King Khalid University Hospital, Riyadh, Saudi Arabia. Similar data are scanty outside Europe and North America, and lacking in Saudi Arabia. Eighty-four children (< or = 16 years) were assigned to an entity of neuromuscular disease following review of the clinical, biochemical and neurophysiological data, and after re-examination of the histological and histochemical features of the muscle biopsies. Of the 84 ascertained cases, 40 (48%) had different forms of muscular dystrophy (MD), 26 (31%) had one of the various types of spinal muscular atrophy (SMA) and two (2.4%) hereditary motor and sensory neuropathy type I. The rest were miscellaneous cases including one (1.2%) with dermatomyositis. Of the dystrophies, severe childhood autosomal recessive muscular dystrophy (SCARMD) was more prevalent (30%) than Duchenne type (25%), conforming with observations from North African countries known to have a high incidence of consanguineous marriages. Family history of other cases of SCARMD included three males and three females, one of whom died at 15 years, and consanguinity was evident in 63%. Congenital MD, inherited in an autosomal recessive pattern, was also common (30%). A history of consanguinity was present in 55%. Of the 26 cases of SMA, type I (Werdnig-Hoffman disease) was the most prevalent (69%). Consanguinity was ascertained in 65% of SMA families and histories revealed another 14 affected siblings. Autosomal recessive forms seem to constitute the bulk of neuromuscular disorders in Saudi Arabia.

Clinical and molecular pathological features of severe childhood autosomal recessive muscular dystrophy in Saudi Arabia

The clinical, biochemical and histochemical features of 14 patients (nine females and five males) with severe childhood autosomal recessive muscular dystrophy (SCARMD) seen at a tertiary hospital in Riyadh from 1982 to 1993 are described. Onset was at 3 to 9 (median 3) years and four of five children aged > 12 years lost ambulation. Five of the eight pairs of parents were closely consanguineous. The mean creatine kinase was 20 times the upper normal limit. Histochemistry of muscle showed dystrophic features in all cases, and dystrophin was positive in all cases examined (N = 6). Three patients (two girls and a boy) were deficient in adhalin, the 50-kDa dystorphin-associated glycoprotein. A boy aged 13 years had rapidly progressing disease. Another boy of the same age (from a family characterized by early onset and slower progression) had normal dystrophin and adhalin. The clinical features conformed with previous observations from Sudan, North Africa and Qatar in the Arabian Peninsula. The disease is common in Saudi Arabia and seems to be more prevalent than Duchenne muscular dystrophy.

Autosomal recessive disorders among Arabs: an overview from Kuwait

Kuwait has a cosmopolitan population of 1.7 million, mostly Arabs. This population is a mosaic of large and small minorities representing most Arab communities. In general, Kuwait's population is characterized by a rapid rate of growth, large family size, high rates of consanguineous marriages within the Arab communities with low frequency of intermarriage between them, and the presence of genetic isolates and semi-isolates in some extended families and Bedouin tribes. Genetic services have been available in Kuwait for over a decade. During this time it has become clear that Arabs have a high frequency of genetic disorders, and in particular autosomal recessive traits. Their pattern is unique and some disorders are relatively common. Examples are Bardet-Biedl and Meckel syndromes, phenylketonuria, and familial Mediterranean fever. A relatively large number of new syndromes and variants have been delineated in Kuwait's population, many being the result of homozygosity for autosomal recessive genes that occurred because of inbreeding. Some of these syndromes have subsequently been found in other parts of the world, negating the concept of the private syndrome. This paper provides an overview of autosomal recessive disorders among the Arabs in Kuwait from a personal perspective and published studies, and highlights the need for genetic services in Arab countries with the goal of prevention and treatment of genetic disorders.