Congenital disorders of glycosylation (CDG) are a group of genetic, mostly multisystem disorders, which often involve the central nervous system. ALG3-CDG is one the some 130 known CDG. Here we report two siblings with a severe phenotype and intrauterine death. Whole-exome sequencing revealed two novel variants in ALG3: NM_005787.6:c.512G>T (p.Arg171Leu) inherited from the mother and NM_005787.6:c.511C>T (p.Arg171Trp) inherited from the father.
Congenital disorders of glycosylation (CDG) are a group of inherited disorders characterized by deficient glycosylation . They are mostly multisystem disorders often involving the central nervous system [2,3,4,5]. ALG3-CDG is a rare disorder, with only 23 patients reported so far [2,3,4,5,6,7,8,9,10,11,12,13]. ALG3 adds the 6th mannose to the growing dolichol-linked oligosaccharide in the ER [2, 14]. Here we report two siblings with a severe malformation syndrome and intrauterine death.
Materials and methods
Genomic DNA was extracted from the muscle tissue of the fetuses and from peripheral blood of their parents. Whole-exome sequencing (WES) and Sanger sequencing were performed according to standard procedures.
Muscle tissues from the patients and a control were washed with phosphate-buffered saline and western blot analysis was performed according to standard procedures.
We report two siblings with severe multisystem dysmorphism who were born to healthy parents. The mother stated that she was never exposed to alcohol, warfarin, or other drugs. The present study was approved by the hospital’s Institutional Review Board, and written informed consent was obtained from the parents. The control tissue was obtained from a healthy fetus who was born with induced labor. The tissue sample was voluntarily donated to our hospital, which is in accordance with the ethical guidelines.
Patient 1 was a male fetus. Multiple congenital abnormalities were detected on prenatal ultrasound scan (USS) at 26 weeks of gestation. The parents decided to terminate the pregnancy at 28 weeks of gestation. The following multiple anomalies were detected: intrauterine growth restriction with short limbs, micrognathia, separation of bilateral renal collecting system, hydramnios, the hands postural fixation, increased cardiothoracic proportion, and fetal edema especially of the scalp tissue. Facial dysmorphism included eyelid ptosis, hypertelorism, short nose, flat nasal bridge, anteverted nares, thin lips, low-set, large and thick ears with malformed pinnae and micrognathia (Fig. 1b (a)). In addition, the patient had a short neck, short limbs, inverted widely spaced nipples; joint contractures, long fingers and toes, ulnar deviation of fingers, adducted thumbs, toes valgus, abnormal subcutaneous fat distribution at neck and buttock, and hirsutism (Fig. 1b (b, e–h)). Radiographic examination showed short long bones with wide metaphyses, short vertebral bodies, short ribs, a narrow thorax, paddle-shaped iliac wings, and bilateral small scapulae (Fig. 1c (a, b)). Fetal karyotype was normal.
This patient was the sister of patient 1 and the mother’s second pregnancy. USS at 18 weeks of gestation showed scalp tissue edema and mildly short limbs. After genetic counseling, the parents decided to terminate the pregnancy at 22 weeks of gestation. Dysmorphism was similar to that in patient 1. Contractures of wrists, knees, and left elbow were milder. Hirsutism and short neck were not observed (Fig. 1b (c, d)). Radiographic examination revealed short limbs, short ribs, a narrow thorax, vertebral hypoplasia, and scoliosis (Fig. 1c (c, d)).
Whole-exome sequencing and Sanger sequencing results
Whole-exome sequencing showed two novel variants in the ALG3 gene: NM_005787.6:c.512G>T (p.Arg171Leu) inherited from the mother and NM_005787.6:c.511C>T (p.Arg171Trp) inherited from the father. The second patient showed the same variants. (Fig. 1a). The effect of NM_005787.6:c.512G>T (p.Arg171Leu) was predicted using the computational tools Sorting Intolerant from Tolerant (SIFT), PolyPhen‑2, and MutationTaster, M-CAP, and the results indicated that the protein variant is “damaging,” “damaging,” “disease causing,” and “damaging,” respectively. The CADD_phred score of the variant is 35. SIFT, PolyPhen‑2, MutationTaster and M-CAP predicted NM_005787.6:c.511C>T (p.Arg171Trp) to be a “damaging,” “damaging,” “disease causing,” and “damaging” variant, respectively. The CADD_phred score of this variant is 33. According to the ACMG criteria, both variants were classified as uncertain significance (PM2, PM5 and PP3).
ALG3 protein expression in the two patients
Western blot analysis of ALG3 in muscle tissues showed a clearly decreased expression in the two patients compared to that in the control (Fig. 2a).
Twenty-three ALG3-CDG patients have been reported so far. These patients showed a broad phenotypical spectrum that mainly includes dysmorphism and neurological, cardiac, skeletal, gastrointestinal, and urogenital abnormalities (summary of reported patients in Table 1). The phenotypes of our patients were already extremely severe in utero and resembled those of the patients reported by Lepais et al.  and Sun et al. . The patient described by Sun et al. died at 19 days and showed multiple dysmorphisms with prominent cerebral, cerebellar, skeletal, cardiac, pulmonary, urogenital, hepatic, and pancreatic involvement. Lepais et al.  reported similarly affected siblings. In one, the abnormalities were detected at 23 weeks of gestation, which was terminated at 25 weeks. In the other, intrauterine growth retardation and short long bones were noted at 13 weeks. The parents refused to terminate the pregnancy, and the child died at 12 days due to heart failure. This severe fetal phenotype resembles that of a patient reported with ALG9-CDG (OMIM: 608776) and patients with Schneckenbecken dysplasia, also known as SLC35D1-CDG (OMIM: 269250).
In conclusion, our cases expand the gene variant database of ALG3-CDG. In addition, we provide a new prenatal genotype-phenotype correlation of ALG3-CDG, which may be beneficial for the future prenatal diagnosis of other CDG cases.
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We are grateful to the patients and their family for providing samples and clinical histories.
This research was supported in part by the 345 Talent Project to YL and National Natural Science Foundation of China (81701462 to YL) and National Key R&D Program of China (2018YFC1002900 to YL).
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The authors declare that they have no conflict of interest.
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Bian, Y., Qiao, C., Zheng, S. et al. ALG3-CDG: lethal phenotype and novel variants in Chinese siblings. J Hum Genet (2020). https://doi.org/10.1038/s10038-020-0798-7