Keywords
PMM2-CDG - cerebral palsy - mutation - South India
Introduction
Congenital disorder of glycosylation (CDG) type Ia (CDG-Ia) [MIM #212065] is an autosomal
recessive disorder of protein N-glycosylation characterized by a phosphomannomutase (PMM) deficiency and mutations
in the (PMM2) gene [MIM #601785] located on chromosome 16p13 that causes CDG (PMM2-CDG) type Ia.[1]
[2]
PMM2-CDG is characterized by central nervous system dysfunction and multiorgan failure.[3]
PMM2 gene catalyzes the isomerization of mannose-6-phosphate to mannose-1-phosphate, which
is a precursor to GDP-mannose necessary for the synthesis of dolichol-pyrophosphate-oligosaccharides
in the early steps of N-glycan synthesis.[4]
[5] About 130 pathological mutations have been described in the PMM2 gene according to the Human Gene Mutation Database (HGMD® professional 2021.3) affecting
the oligosaccharide precursor transfer in the endoplasmic reticulum, and PMM2-CDG II affects the transfer in the Golgi apparatus.[6]
[7]
Hypotonia, stroke-like episodes, and peripheral neuropathy are also associated with
the condition that typically develops during infancy; young individuals with PMM2-CDG may have a moderate intellectual disability and unsteady or abnormal gait.[2]
[8] The childhood mortality rate is approximately 15 to 30%, and permanent neurological
disabilities develop in surviving patients.[9] This case study describes the clinical and molecular findings of a young girl from
South India affected with cerebral palsy (CP) phenotypes carrying PMM2-CDG mutation.
Clinical Report
A 12-year-old female from South India was born preterm to healthy consanguineous parents.
Her birth weight was 2,500 g and presented with a delayed birth cry. Since birth,
she presented generalized hypotonia. No history of neonatal jaundice or neonatal hypoxia
was reported. The average tone of the muscle motor sensor, an inaccurate gait pattern,
and a bilateral flexed knee was observed. No ataxia or cerebellar syndrome was observed.
Since an early age, she presented inadequate speech and language, learning difficulties
with mild mental retardation and dependence on several activities of daily life, psychomotor
and developmental delay, and inability to walk. No history of hearing difficulties
was reported. The ophthalmological analysis showed squint vision. After explaining
the purposes of the study, informed consent was obtained from the parents to perform
molecular diagnosis, and to publish the data on the patient. Blood samples were collected
from the patient and her family members by a Phlebotomist. Genomic DNA was extracted
from peripheral blood by using PureLink Genomic DNA Mini Kit (Thermo Fisher Scientific,
United States) according to the manufacturer's instructions. Whole-exome sequencing
(WES) was performed for the proband. The exome libraries were constructed using the
Ion Ampliseq exome RDY kit (Thermo Fisher Scientific, United States) and sequenced
on the Ion Proton sequencing platform (Life Technologies, United States). Variants
were called using the Torrent Variant Caller plug-in using the software console of
the Torrent server. Variants were annotated using Ion Reporter (Thermo Fisher Scientific,
United States) using the human reference genome (hg19). Pathogenicity of candidate
variants was evaluated using Genome Aggregation Database (https://gnomad.broadinstitute.org/), ClinVar (https://www.ncbi.nlm.nih.gov/clinvar/), and literature review. Sanger sequencing was performed for variant validation of
the proband and the parents by amplifying the PMM2 region (rs80338708) using the primers (forward: 5′-ACAGATCTTCGCAAGAACATCGT-3′, reverse:5′-
CACGTTAGGAGAACAGCAGTTCA-3′) for a total volume of 10 μL. An initial denaturation step
at 95°C for 2 minutes was followed by 35 cycles of 98°C for 25 seconds, 67°C for 45 seconds
for annealing, 72°C for 30 seconds for elongation, and final extension at 72°C for
7 minutes. The PCR products were evaluated using a 2% agarose gel electrophoresis.
PCR products were labeled with BigDye Terminator v3.1 Cycle Sequencing Kit (Applied
Biosystems, United States). The above-mentioned PCR primer (PMM2 Forward) was used as a sequencing primer and then analyzed by ABI 3500 Genetic Analyser
(Applied Biosystems, United States). Sequence data were analyzed with Seqscape v3
software (Applied Biosystems, United States).
Discussion
We describe the case of a girl with CP phenotypes who had missense variations in the
PMM2 gene that was identified by WES. The patient presented strong genotypic and phenotypic
features of typical PMM2-CDG type 1a ([Table 1]). WES identified the pathogenic homozygous variant [NM_000303.3] c.710C > T p.T237M
(rs80338708) in the patient and also identified heterozygous variants in the parents
([Fig. 1]). She exhibited age-inadequate speech and language skills; weakness in lower limbs
was also observed in the patient. Spastic diplegia was observed that impairs the legs
but does not usually affect the arms; but the patient in this study has weakness in
the hands because of low muscle tone. Hip problems are also common in spastic diplegic
patients. The spastic type of CP is more commonly associated with ocular abnormalities.[10] Strabismus was seen in the patient that is associated with neurodevelopmental disorders
such as CP, Down's syndrome, intellectual disability, and white matter damage of prematurity.[11]
[12]
[13]
Table 1
Clinical features and genotype
|
Sample name
|
CP_39A
|
|
Gender
|
Female
|
|
Age
|
12 years
|
|
Ethnic
|
South Asian
|
|
Mutation
|
PMM2 c.710C > T237M (Homozygous)
|
|
Consanguinity
|
+
|
|
Preterm birth
|
+
|
|
Birth cry delay
|
+
|
|
Neonatal hypotonia
|
+
|
|
Neonatal hypoxia
|
–
|
|
Neonatal jaundice
|
–
|
|
Developmental delay
|
+
|
|
Mental retardation
|
+
|
|
Strabismus
|
+
|
|
Delayed speech and language
|
+
|
|
Hearing loss
|
–
|
|
Paralysis or weakness of limbs
|
+
|
|
Neuromuscular scoliosis
|
+
|
|
Renal involvement
|
Unknown
|
|
Liver involvement
|
Unknown
|
|
Heart problem
|
Unknown
|
Fig. 1 Pedigree and chromatograms generated by Sanger sequencing of the PMM2 c.710C > T mutation detected in this study.
On chromosome 16p13.2, mutations in PMM2 gene that cause CDG-Ia were identified.[1] This work is the first to report the T237M variant of the PMM2 gene in a patient with CDG-Ia phenotypes (https://www.chop.edu/conditions-diseases/congenital-disorders-glycosylation-cdg) in a South Indian girl ([Table 1]). The parents carried the heterozygous recessive variant of PMM2 c.710 C > T that was expressed as the homozygous genotype in their child (patient;
[Fig. 1]). Mutations of the PMM2 gene cause PMM2 deficiency, which is the most common autosomal recessive CDG.[14] Several missense mutations associated with a recessive disease are observed in PMM2.[15] Predetermined maternal factors such as heredity, malnutrition, and metabolism may
lead to physical or mental problems, or even death.[16] Premature birth and low birth weight, which are linked with numerous health problems
later in life, also can be influenced by birth defects. However, factors such as adolescent
pregnancy (<19 years),[17] advanced maternal age (>35 years),[18] and poor access to medical care contribute as well.[19] Also, birth defects are a contributing factor to some miscarriages and stillbirths.[20] For that reason, some factors affect the prenatal developmental stage of fetal abnormalities.
In this study the mother has a history of one miscarriage after the patient was born
([Fig. 1]). PMM2-CDG is not thoroughly diagnosed, since the phenotypes are similar to CP. Therefore,
clinical awareness and molecular diagnosis should be performed to screen couples with
infertility or miscarriage issues[21] and they should be appropriately counseled on the potential risk before subsequent
pregnancies. In conclusion, we describe the first South Indian patient with autosomal
recessive CDG-Ia with PMM2 c.710 C > T, T237M mutation inherited from carrier parents in accordance with the
PMM2-CDG type Ia. This study emphasizes the importance of considering WES in patients
with developmental disabilities or other neurological conditions.
