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Neuromuscular disorders
Published in Angus Clarke, Alex Murray, Julian Sampson, Harper's Practical Genetic Counselling, 2019
The X-linked form of Charcot-Marie-Tooth disease must be borne in mind when considering an isolated male case or a pedigree suggestive of X-linkage. Molecular defects in connexin 32 have been found in this type. Nerve conduction is often variable in this form, and usually normal in heterozygous females, who may be variably affected clinically. Friedreich ataxia (autosomal recessive, see Chapter 14) may also show prominent neuropathic features.
Sexual Differentiation of a Neuromuscular System
Published in Akira Matsumoto, Sexual Differentiation of the Brain, 2017
Scott E. Christensen, S. Marc Breedlove, Cynthia L. Jordan
Electrotonic coupling and its cellular substrate — gap junctions — are typically not detected between adult mammalian motoneurons.65 A preliminary report by Collins and Erichsen,66 however, suggested that adult SNB motoneurons are exceptional in that they are electrically coupled. It was also shown, on the basis of electron microscopy, that gap junctional plaques are present between adjacent SNB motoneurons and that their number and size are reduced in the absence of adult androgens.58 It was later demonstrated by in situ hybridization that androgen also regulates the expression of connexin 32 (Cx32), a gap junction gene expressed by SNB motoneurons, suggesting that this underlies the difference in gap junction number. Castration results in a significant reduction in Cx32 mRNA expression in SNB motoneuronal soma and proximal dendrites; T replacement restores these values.67 Indeed, T treatment for 2 days was sufficient to restore the amount of Cx32 mRNA to that seen in intact males. The modulation of this gene by androgen appears selective to motor pools that are sexually dimorphic: RDLN motoneurons produce Cx32 yet T treatment does not affect its expression. While Cx32 appears to be a required molecular component for gap junctions between some cells,68 Cx32 also appears to be involved in pore formation within cells.69,70 Thus androgen-regulated Cx32 may not be the exclusive substrate for associated changes in gap junctions.
Neurogenetics
Published in John W. Scadding, Nicholas A. Losseff, Clinical Neurology, 2011
Sonia Gandhi, Sarah Tabrizi, Nicholas Wood
X-linked CMT (CMT1X) is the second most common form of CMT, accounting for 10 per cent of CMT. It affects males more than females and is caused by mutations in the gap junction protein beta 1 gene encoding the protein connexin 32. The nerve conduction velocity is slowed as with all forms of CMT1, but the velocity tends to be in the intermediate range at 25–40 m/s rather than the severe range. Connexin 32 is expressed also in the CNS and therefore occasional features, such as deafness or extensor plantars, may be observed.
Cell-cell junctions in developing and adult tendons
Published in Tissue Barriers, 2020
Sophia K. Theodossiou, Jett B. Murray, Nathan R. Schiele
Connexin-43 expression was found to overlap with growth/differentiation factor (GDF)-5 expression during embryonic mouse limb development.68 GDF-5 and connexin-43 expression were localized to the condensing digit and long bones of the hindlimb at E12.5, the perichondral regions of the forelimb at E13.5, and to the elbow and hip joint surrounding the femoral head from E12.5 to E14.5.68 Colocalized expression of GDF-5 and connexin-43 was also detected in tendons of the hip at E14.5, and around the tendons of each toe at E15.5, indicating that GDF-5 and connexin-43 are both present in embryonic tendon.68 Together these results highlight that connexin-32 and −43 gap junction proteins are present in embryonic tendon. However, the specific contributions of connexins to embryonic tendon development remain unknown, and future studies correlating connexin expression with functional cellular communication and tenogenesis are needed.