Three novel COLQ mutations and variation of phenotypic expressivity due to G240X

OBJECTIVE

To determine the molecular basis and consequences of endplate (EP) acetylcholinesterase (AChE) deficiency.

BACKGROUND

The EP species AChE is an asymmetric enzyme consisting of a tail subunit composed of three collagenic strands (ColQ), each attached to a tetramer of catalytic subunits. The tail subunit is essential for insertion of AChE into the synaptic basal lamina. Human EP AChE deficiency is caused by mutations in COLQ. The authors report three novel COLQ mutations in eight kinships.

METHODS

Immunocytochemistry, electron microscopy, microelectrode recordings, mutation analysis, and expression studies in COS cells were employed.

RESULTS

Two mutations (275insC and Q211X) were heterozygous in one patient. EP studies in this patient revealed no EP AChE, small nerve terminals, reduced presynaptic membrane length, as well as abnormally low-evoked quantal release. The third mutation (G240X) was homozygous in six Palestinian Arab families of the same tribe and in an Iraqi Jewish patient. Expression studies of the three mutations in COS cells indicate that each abrogates formation of insertion competent asymmetric AChE. Although the three mutations have identical predicted consequences at the EP, their phenotypic expressivity varies as regards age at onset, rate of progression, and severity of symptoms.

CONCLUSIONS

1) After mutations in the AChR epsilon subunit, mutations in COLQ are emerging as second most common cause of congenital myasthenic syndromes. 2) A founder effect is likely for G240X in the Palestinian Arab families. 3) That mutations predicting total absence of AChE from the EP have variable phenotypic expressivity suggests that modifying genes or environmental factors can partially compensate for EP AChE deficiency.

Differences in cord serum retinol concentrations by ethnic origin in the Negev (southern Israel)

Subclinical vitamin A deficiency is related to increased morbidity and mortality in infants and children. Previous studies indicate that the traditional diet of Moslem Bedouins, an important ethnic group in Southern Israel, is low in vitamin A content. Cord serum retinol (vitamin A) concentration was measured by HPLC in samples from 251 apparently healthy (birth weight > 2500 g, gestational age > 37 weeks) neonates with no abnormal perinatal events, 138 Jews and 113 Bedouins. Retinol < 15 micrograms/dl was measured in a total of 14% of infants: in 7% of Jewish and 26% of Bedouin newborns (P < 0.001). However, mean cord serum retinol was only slightly lower in Bedouins than in Jews (30 +/- 26 vs. 37 +/- 27 micrograms/dl mean +/- S.D., n.s.). Cord serum retinol was not related to socioeconomic indices. Cord serum retinol < 15 micrograms/dl was measured in 25% and in 12% of infants with birth weight less than and equal or greater than 3000 g, respectively (P = 0.01), and in 28% and 13% of infants with gestational age 37-38 weeks and 39-41 weeks, respectively (P = 0.03). Low cord serum retinol was found to be prevalent in Southern Israel, particularly in Bedouin infants. In the population of healthy neonates studied, very low cord serum retinol concentrations were found more frequently in infants born with a lower weight and/or after a shorter gestation.