Genetic Analyses
Fluorescently labeled microsatellite markers located close to the
respective genes (Table S1) excluded linkage of the disorder toGNPTAB (OMIM#607840), GNPTG (OMIM#607838), IDUA(OMIM#611542) and ARSB (OMIM#611542) for family NMD02. Analyses
of the filtered exome data revealed three novel homozygous exonic
variants located on chromosome 14q32 (Table S6) which also segregated
with the phenotype in family NMD02 (Figure 1-2). OnlyTMEM251 variant c.133C>T;p.(Arg45Trp) was predicted
to be damaging by all five prediction programs and affected an amino
acid which was fully conserved in the orthologous proteins (Figure 3A).
This variant was absent in all public databases and from 400 ethnically
matched control chromosomes. The known genetic causes of various forms
of mucopolysaccharidosis and mucolipidosis were also excluded by
analyses of exome data for family NMD02 (Table S1).
We identified five regions of shared homozygosity located on different
chromosomes from the exome data of the two affected individuals (Figure
S1). Sequencing of the variants located in these regions revealed that
only variants present on chromosome 14q32 (Table S2, Table S6 and data
not shown) segregated with the phenotype with a LOD score of 3.2 atθ = 0. Moreover, no variants were identified by Sanger sequencing
in those exons which were located within chromosome 14q32 region of
shared homozygosity (Figure S1) and had not been covered by exome
sequencing (Table S2).
Analysis of the trio exome sequencing data of family ID01 revealed one
homozygous insertion variant c.215dupA;p.(Tyr72Ter) in TMEM251 in
the patient, for which the parents were heterozygous carriers (Figure 1
and 2). None of the other 23 individuals from the pedigree were found to
be homozygous for the variant. Moreover, this variant was absent from
all public databases. The variant identified in family NMD02 was
deposited in LOVD (#0000601066) and the variant identified in family
ID01 was deposited in ClinVar (SCV000998897).