A Roma founder BIN1 mutation causes a novel phenotype of centronuclear myopathy with rigid spine

Abstract

Objective: To describe a large series of BIN1 patients, in which a novel founder mutation in the Roma population of southern Spain has been identified.

Methods: Patients diagnosed with centronuclear myopathy (CNM) at 5 major reference centers for neuromuscular disease in Spain (n = 53) were screened for BIN1 mutations. Clinical, histologic, radiologic, and genetic features were analyzed.

Results: Eighteen patients from 13 families carried the p.Arg234Cys variant; 16 of them were homozygous for it and 2 had compound heterozygous p.Arg234Cys/p.Arg145Cys mutations. Both BIN1 variants have only been identified in Roma, causing 100% of CNM in this ethnic group in our cohort. The haplotype analysis confirmed all families are related. In addition to clinical features typical of CNM, such as proximal limb weakness and ophthalmoplegia, most patients in our cohort presented with prominent axial weakness, often associated with rigid spine. Severe fat replacement of paravertebral muscles was demonstrated by muscle imaging. This phenotype seems to be specific to the p.Arg234Cys mutation, not reported in other BIN1 mutations. Extreme clinical variability was observed in the 2 compound heterozygous patients for the p.Arg234Cys/p.Arg145Cys mutations, from a congenital onset with catastrophic outcome to a late-onset disease. Screening of European Roma controls (n = 758) for the p.Arg234Cys variant identified a carrier frequency of 3.5% among the Spanish Roma.

Conclusion: We have identified a BIN1 founder Roma mutation associated with a highly specific phenotype, which is, from the present cohort, the main cause of CNM in Spain.

Figure 1. BIN1 families: Pedigrees and haplotype analysis

A conserved haplotype (red) is shared by all families identified among normal controls, which segregates with the p.Arg234Cys mutations. A second haplotype, shared by families 1 and 6 segregates with the p.Arg145Cys mutation (green). Arrow: recombination in family 4. Arrowhead: position of BIN1 in relation to the markers used for the haplotype analysis.

Figure 2. Rigid spine

(A–C) Cervical rigid spine. (D and E) Dorsal and lumbar rigid spine.

Figure 3. BIN1 patients’ muscle imaging

(A) Cervical T1 MRI of a normal control in sagittal view showing normal signal intensity in paravertebral muscles (stars). (B, C, and E–J) Axial muscle scans showing prominent to complete fat replacement in paravertebral muscles at the various levels examined (stars). (B) Cervical T1 MRI, sagittal view, of patient 4.1. (C) Cervical T1 MRI, sagittal view, of patient 9.1. (D) Lumbar T1 MRI of a normal control, sagittal view, showing normal signal intensity of paravertebral muscles (stars). (E) Lumbar T1 MRI, sagittal view, in patient 10.1. (F) Lumbar T1 MRI, sagittal view, of patient 13.1. (G) CT scan at the thoracic level in patient 10.1. (H) CT scan at the thoracic level of patient 13.1. (I) CT scan at the dorsal level, axial view, of patient 5.1. (J) Lumbar MRI, sagittal view, patient 2.1. (K–N) Lower limbs muscle scans showing fat replacement predominantly involving the posterior compartment of the thighs (top pictures) and soleus and medial gastrocnemius in the lower legs (bottom pictures). (K) T1 MRI, patient 5.1; (L) T1 MRI, patient 7.2; (M) CT scan, patient 8.1; (N) CT scan, patient 2.1; (O) muscle T1 MRI of patient 1.1 showing diffuse involvement of thighs and lower legs.

Figure 4. Histopathologic findings in BIN1 patients

(A–C) Typical centronuclear myopathy histopathologic pattern with frequent central nuclei, some forming clusters and endomysial fibrosis with fat replacement. (D) Atypical case with infrequent central nuclei, few internal nuclei, and occasional central vacuoles. (E–H) Congenital-onset case with myotubular features showing central nuclei (E), central accumulations of glycogen (F), a peripheral rim devoid of oxidative activity (G), and type I hypotrophy (H). (I–P) Serial sections of the same areas stained with different techniques to demonstrate frequent central areas devoid of H&E staining (I), not containing glycogen (J), or myofibrils (K). These areas show a strong reactivity to SHD (L) and NADH (M), and they are negative to spectrin (N) and emerin (O) immunostains. Dystrophin immunoreactive material is present in central areas. (A) Patient 1.1, biceps (H&E). (B) Patient 9.1, deltoid (H&E). (C) Patient 13.1, biceps (H&E). (D) Patient 2.1, biceps (H&E). (E–H) Patient 6.1, quadriceps (E: H&E; F: PAS; G: NADH; H: ATPase 4.6). (I–P) Patient 7.2, deltoid (I: H&E; J: PAS; K: ATPase 9.4; L: SDH; M: NADH; N: spectrin; M: emerin; P: dystrophin C-terminal domain). ATPase = adenosine triphosphatase; H&E = hematoxylin & eosin; NADH = nicotinamide adenine dinucleotide; PAS = periodic acid–Schiff; SDH = succinate dehydrogenase.