Retinitis pigmentosa caused by mutations in the ciliary MAK gene is relatively mild and is not associated with apparent extra-ocular features.
OBJECTIVE
Defects in MAK, encoding a protein localized to the photoreceptor connecting cilium, have recently been associated with autosomal recessive retinitis pigmentosa (RP). The aim of this study is to describe our detailed clinical observations in patients with MAK-associated RP, including an assessment of syndromic symptoms frequently observed in ciliopathies.


METHODS
In this international collaborative study, 11 patients carrying nonsense or missense mutations in MAK were clinically evaluated, including extensive assessment of the medical history, slit-lamp biomicroscopy, ophthalmoscopy, kinetic perimetry, electroretinography (ERG), spectral-domain optical coherence tomography (SD-OCT), autofluorescence imaging and fundus photography. Additionally, we used a questionnaire to evaluate the presence of syndromic features and tested the olfactory function.


RESULTS
MAK-associated RP is not associated with syndromic features, not even with subclinical dysfunction of the olfactory apparatus. All patients experienced typical RP symptoms of night blindness followed by visual field constriction. Symptoms initiated between childhood and the age of 43 (mean: 23 years). Although some patients experienced vision loss, the visual acuity remained normal in most patients. ERG and ophthalmoscopy revealed classic RP characteristics, and SD-OCT demonstrated thinning of the overall retina, outer nuclear layer and photoreceptor-pigment epithelium complex.


CONCLUSIONS
Nonsense and missense mutations in MAK give rise to a non-syndromic recessive RP phenotype without apparent extra-ocular features. When compared to other retinal ciliopathies, MAK-associated RP appears to be relatively mild and shows remarkable resemblance to RP1-associated RP, which could be explained by the close functional relation of these proteins.
Department of Ophthalmology, Radboud University Medical Center, Nijmegen, The Netherlands.
Ramon A C
RA
van Huet
Anna M
AM
Siemiatkowska
Riza K
RK
Özgül
Didem
D
Yücel
Carel B
CB
Hoyng
Eyal
E
Banin
Anat
A
Blumenfeld
Ygal
Y
Rotenstreich
Frans C C
FC
Riemslag
Anneke I
AI
den Hollander
Thomas
T
Theelen
Rob W J
RW
Collin
L Ingeborgh
LI
van den Born
B Jeroen
BJ
Klevering
D000328:Adult; D000368:Aged; D018389:Codon, Nonsense; D004596:Electroretinography; D005260:Female; D005451:Fluorescein Angiography; D006801:Humans; D008297:Male; D008875:Middle Aged; D020125:Mutation, Missense; D010375:Pedigree; D010641:Phenotype; D055212:Photoreceptor Connecting Cilium / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D012174:Retinitis Pigmentosa / Q000235:genetics* / Q000473:pathology; D011795:Surveys and Questionnaires; D041623:Tomography, Optical Coherence; D058609:Visual Field Tests; D055815:Young Adult
D018389:Codon, Nonsense; D017346:Protein Serine-Threonine Kinases; C081931:MAK protein, human
MAK; clinical variability; non-syndromic; retinitis pigmentosa