Mutations in FKRP result in a range of phenotypes that are not fully explained by genotype, although those homozygous for the c.C826A mutation have later onset of symptoms.
For example, patients with clearly deleterious splicing mutations on the other chromosome (c.3523 1G>A in patient #11, c.768G>T in patient #14, and c.4540 2A>G in patient #27) had an earlier disease onset and rapid progression, whereas patients with a "milder" second mutation had later onset and slower disease progression.
Further duplications and loss-of-function mutations have later led to the emergence of several CLPs, some of which are found in all mammals, while others are specific to particular species.
Conversely, the mean evolutionary rate estimates tend to decrease with the addition of data over time, suggesting that many early deleterious/neutral mutations may have later been purged from the population through purifying selection [ 3, 5, 14].
We sought to determine whether a cohort of mature individuals with the m.1555A>G mutation have hearing loss by their mid-40s because the mutation has been reported to cause later-onset less severe hearing loss in people who have never been exposed to aminoglycosides.
Another family with this mutation has recently been reported with HH in childhood and later-onset diabetes [ 19].
Muller's ratchet can be reversed by recombination only if a mutation has not been fixed (unless eDNA turnover is very slow, as described later in this article).
This is not surprising: the bigger the effect a mutation has, the bigger the chance that it will be something disruptive, so mutations that have dramatic effects are likelier to be harmful than mutations that produce modest changes.
The mutation has the opposite effect of the one found in Colombia: people with the mutation are more likely to retain sharp cognitive abilities well into their nineties.
Two additional dominant missense mutations, H1901L [ 10] and L1793P [ 22], have later been reported to cause myosin storage myopathy.
