Absence of alpha-sarcoglycan and novel missense mutations in the alpha-sarcoglycan gene in a young British girl with muscular dystrophy

Patterns of Clinical Progression Among Patients With Autosomal Recessive Limb-Girdle Muscular Dystrophy: A Systematic Review

OBJECTIVES

As the clinical course of autosomal recessive limb-girdle muscular dystrophy (LGMDR) is highly variable, this study characterized the frequency of loss of ambulation (LOA) among patients by subtype (LGMDR1, LGMDR2, LGMDR3-6, LGMDR9, LGMDR12) and progression to cardiac and respiratory involvement among those with and without LOA.

METHODS

Systematic literature review.

RESULTS

From 2929 abstracts screened, 418 patients were identified with ambulatory status data (LOA: 265 [63.4%]). Cardiac and/or respiratory function was reported for 142 patients (34.0%; all with LOA). Among these, respiratory involvement was most frequent in LGMDR3-6 (74.1%; mean [SD] age 23.9 [11.0] years) and cardiac in LGMDR9 (73.3%; mean [SD] age 23.7 [17.7] years). Involvement was less common in patients without LOA except in LGMDR9 (71.4% respiratory and 52.4% cardiac).

CONCLUSIONS

This study described the co-occurrence of LOA, cardiac, and respiratory involvement in LGMDR and provides greater understanding of the clinical progression of LGMDR.

Progression to Loss of Ambulation Among Patients with Autosomal Recessive Limb-girdle Muscular Dystrophy: A Systematic Review

Background

The impact of age at autosomal recessive limb girdle muscular dystrophy (LGMDR) onset on progression to loss of ambulation (LOA) has not been well established, particularly by subtype.

Objectives:

To describe the characteristics of patients with adult-, late childhood-, and early childhood-onset LGMDR by subtype and characterize the frequency and timing of LOA.

Methods:

A systematic review was conducted in MEDLINE, Embase and the Cochrane library. Frequency and timing of LOA in patients with LGMDR1, LGMDR2/Miyoshi myopathy (MM), LGMDR3-6, LGMDR9, and LGMDR12 were synthesized from published data.

Results:

In 195 studies, 695 (43.4%) patients had adult-, 532 (33.2%) had late childhood-, and 376 (23.5%) had early childhood-onset of disease across subtypes among those with a reported age at onset (n = 1,603); distribution of age at onset varied between subtypes. Among patients with LOA (n = 228), adult-onset disease was uncommon in LGMDR3-6 (14%) and frequent in LGMDR2/MM (42%); LGMDR3-6 cases with LOA primarily had early childhood-onset (74%). Mean (standard deviation [SD]) time to LOA varied between subtypes and was shortest for patients with early childhood-onset LGMDR9 (12.0 [4.9] years, n = 19) and LGMDR3-6 (12.3 [10.7], n = 56) and longest for those with late childhood-onset LGMDR2/MM (21.4 [11.5], n = 36).

Conclusions:

This review illustrated that patients with early childhood-onset disease tend to have faster progression to LOA than those with late childhood- or adult-onset disease, particularly in LGMDR9. These findings provide a greater understanding of progression to LOA by LGMDR subtype, which may help inform clinical trial design and provide a basis for natural history studies.

Concomitant alpha- and gamma-sarcoglycan deficiencies in a Turkish boy with a novel deletion in the alpha-sarcoglycan gene

Limb-girdle muscular dystrophy type 2D (LGMD-2D) is caused by autosomal recessive defects in the alpha-sarcoglycan gene located on chromosome 17q21. In this study, we present a child with alpha-sarcoglycanopathy and describe a novel deletion in the alpha-sarcoglycan gene. A 5-year-old boy had a very high serum creatinine phosphokinase level, which was determined incidentally, and a negative molecular test for the dystrophin gene. Muscle biopsy showed dystrophic features. Immunohistochemistry showed that there was diminished expression of alpha- and gamma-sarcoglycans. DNA analysis revealed a novel 7 bp homozygous deletion in exon 3 of the alpha-sarcoglycan gene. His parents were consanguineous heterozygous carriers of the same deletion. We believe this is the first confirmed case of primary alpha-sarcoglycanopathy with a novel deletion in Turkey. In addition, this study demonstrated that both muscle biopsy and DNA analysis remain important methods for the differential diagnosis of muscular dystrophies because dystrophinopathies and sarcoglycanopathies are so similar.

Sarcolemmal alpha and gamma sarcoglycan protein deficiencies in Turkish siblings with a novel missense mutation in the alpha sarcoglycan gene

BACKGROUND

The sarcoglycan alpha gene, also known as the adhalin gene, is located on chromosome 17q21; mutations in this gene are associated with limb-girdle muscular dystrophy type 2D. We describe two Turkish siblings with findings consistent with limb-girdle muscular dystrophy type 2D. The evaluation excluded a dystrophinopathy, which is the most common form of muscular dystrophy.

PATIENTS

Both siblings had very high levels of creatinine phosphokinase and negative molecular tests for deletions and duplications of the dystrophin gene. The older boy presented at 8 years of age with an inability to climb steps and an abnormal gait. His younger brother was 5 years old and had similar symptoms. The muscle biopsy evaluation was performed only in the older brother.

RESULTS

The muscle biopsy showed dystrophic features as well as a deficiency in the expression of two different glycoproteins: the alpha sarcoglycan and the gamma sarcoglycan. Sarcolemmal expressions of dystrophin and other sarcoglycans (beta and delta) were diffusely present. DNA analysis demonstrated the presence of previously unknown homozygous mutations [c.226 C > T (p.L76 F)] in exon 3 in the sarcoglycan alpha genes of both siblings. Similar heterozygous point mutations at the same locus were found in both parents, but the genes of beta, delta, and gamma sarcoglycan were normal in the remaining family members.

CONCLUSIONS

We describe two siblings with limb-girdle muscular dystrophy type 2D with a novel missense mutation. These patients illustrate that the differential diagnosis of muscular dystrophies is impossible with clinical findings alone. Therefore, a muscle biopsy and DNA analysis remain essential methods for diagnosis of muscle diseases.

Heart involvement in muscular dystrophies due to sarcoglycan gene mutations

Mutations in the sarcoglycan genes cause autosomal-recessive muscular dystrophies. Because sarcoglycan genes and their protein products are highly expressed both in skeletal and cardiac muscle, patients with these mutations might be expected to be at risk to develop dilated cardiomyopathy. We therefore studied 13 patients with alpha-, beta-, gamma-sarcoglycan gene mutations by thorough cardiological assessment. Electrocardiographic or echocardiographic abnormalities were observed in about 30% of cases showing a severe course of muscular dystrophy. No correlation was found between the presence of cardiac abnormalities and the type of mutation or sarcoglycan gene involved. The cardiac involvement was never severe, but it may be detected in early stages of the muscle disease. The absence of overt cardiac dysfunction may be due to lower sarcoglycan protein expression in cardiac than skeletal muscle or to less sarcolemmal instability at the myocardial level, possibly related to the different distribution of forces generated by contraction of the myocardium with respect to proximal limb-girdle muscles.